LTC3455/LTC3455-1 complete power management solutions variety portable

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LTC3455/LTC3455-1 complete power management solutions variety portable

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LTC3455/LTC3455-1 Dual DC/DC Converter with Power Manager Li-Ion Battery Charger DESCRIPTION
LTC3455/LTC3455-1 complete power management solutions variety portable applications. These devices contain synchronous step-down DC/DC converters, power controller, full-featured Li-Ion battery charger, Swap output, low-battery indicator, numerous internal protection features. LTC3455/LTC3455-1 provide small, simple solution obtaining power from three different power sources: single-cell Li-Ion battery, port, wall adapter. Current drawn from accurately limited under conditions. Whenever wall adapter present, battery charger enabled internal power device drawn from appropriate external power source. outputs discharged ground during shutdown provide complete output disconnect. These devices available 24-pin exposedpad package.
LTC, Land Burst Mode registered trademarks Linear Technology Corporation. Swap trademark Linear Technology Corporation. other trademarks property their respective owners. Protected U.S. Patents including 6522118.
Seamless Transition between Input Power Sources: Li-Ion Battery, USB, Wall Adapter Accurate Current Limiting (500mA/100mA) High Efficiency DC/DC Converters: Thermal Regulation Maximizes Battery Charge Rate without Risk Overheating Full-Featured Li-Ion Battery Charger with 4.2V Float Voltage LTC3455 4.1V LTC3455-1 4.1V Float Voltage (LTC3455-1) Improves Battery Life High Temperature Safety Margin SwapOutput SDIO Memory Cards Pin-Selectable Burst Mode® Operation Output Disconnect: Outputs Discharged Ground During Shutdown Available 0.75mm 24-Pin Package
APPLICATIONS
Handheld Computers Digital Cameras Players
TYPICAL APPLICATION
4.7F WALL 4.7F 3.32k 5.6V CONTROLLER SUSPEND USBHP VMAX MODE HSON PWRON PBSTAT LTC3455/LTC3455-1 CHRG WALLFB 0.1F 1.24k 2.49k VBAT 4.7F SINGLE CELL Li-ION 3.3V 4.2V TIMER PROG 10pF VBAT 2.49M 806k
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Efficiency
1.8V
SWITCHER VOUT2 3.3V
1000
POWER LOSS (mW) EFFICIENCY VBAT 3.6V LOAD CURRENT (mA) 1000 POWER LOSS BOTH OUTPUTS SWITCHER VOUT1 1.8V
ON/OFF 3.3V,
4.7H 249k 80.6k 3.3V 0.5A
1.8V
4.7H 10pF 100k 80.6k 1.8V 0.4A
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LTC3455/LTC3455-1 ABSOLUTE MAXIMUM RATINGS
(Note
CONFIGURATION
VIEW PWRON PBSTAT MODE HSON VMAX WALLFB VBAT PROG TIMER CHRG USBHP SUSPEND
Transient Duty Cycle 1%): VMAX Voltages -0.3V Steady State: VBAT, VMAX, Voltages -0.3V SW1, Voltages -0.3V (VMAX 0.3V) TIMER Voltage -0.3V (VMAX 0.3V) PWRON, ON2, HSON Voltages -0.3V PBSTAT, RST, CHRG, Voltages -0.3V HSI, Voltages -0.3V MODE, USBHP SUSPEND Voltages. -0.3V WALLFB, PROG Voltages -0.3V FB1, Voltages -0.3V Junction Temperature 125°C Operating Temperature Range (Note -40°C 85°C Storage Temperature Range- -65°C 125°C
PACKAGE 24-LEAD (4mm 4mm) PLASTIC TJMAX 125°C, 37°C/W, 4.3°C/W EXPOSED (PIN GND, MUST SOLDERED
ORDER INFORMATION
LEAD FREE FINISH LTC3455EUF#PBF LTC3455EUF-1#PBF TAPE REEL LTC3455EUF#TRPBF LTC3455EUF-1#TRPBF PART MARKING 3455 34551 PACKAGE DESCRIPTION 24-Lead (4mm 4mm) Plastic 24-Lead (4mm 4mm) Plastic TEMPERATURE RANGE -40°C 85°C -40°C 85°C
Consult Marketing parts specified with wider operating temperature ranges. Consult Marketing information non-standard lead based finish parts. more information lead free part marking, http://www.linear.com/leadfree/ more information tape reel specifications,
ELECTRICAL CHARACTERISTICS
PARAMETER Battery Undervoltage Lockout Voltage Battery Undervoltage Lockout Hysteresis VBAT Quiescent Current (Note Burst Mode, Battery Powered Mode, Battery Powered Powered Wall Powered Shutdown Threshold PWRON Threshold Threshold MODE Threshold WALLFB Threshold Voltage WALLFB Hysteresis WALLFB Rising CONDITIONS VBAT Rising
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VBAT 3.6V, VMAX 3.6V, VPWRON open, VON2 VUSB VWALLFB unless otherwise noted.
VON2 VMODE Switching VON2 VMODE Switching VUSB Charger VWALL 1.5V, VMAX 4.5V, Charger VPWRON VMAX
UNITS
1.26
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1.20
1.23
LTC3455/LTC3455-1 ELECTRICAL CHARACTERISTICS
PARAMETER Pullup Current PWRON Pulldown Current Pulldown Current MODE Pullup Current WALLFB Input Bias Current PBSTAT Voltage Voltage Pulse Duration Battery-VMAX PMOS VMAX PMOS Switch On-Resistance VMAX Switch Current Limit VMAX Switch Current Limit Startup Gain Block Threshold Voltage Pin/FB2 Voltage Difference Input Bias Current Sink Current Voltage Switching Regulators FB1, Voltage FB1, Voltage Line Regulation FB1, Voltage Burst Mode Hysteresis FB1, Input Bias Current Switching Frequency PMOS Switch On-Resistance NMOS Switch On-Resistance PMOS Switch Current Limit Power Manager Undervoltage Lockout Voltage Undervoltage Lockout Hysteresis Minimum Voltage Charge Battery PMOS Switch On-Resistance Current Limit Suspend Mode Bias Current SUSPEND Threshold USBHP Threshold SUSPEND Pulldown Current USBHP Pulldown Current VSUSPEND 0.5V VUSBHP 0.5V VUSB VUSB VUSBHP VUSB VUSBHP VUSB VSUSPEND
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VBAT 3.6V, VMAX 3.6V, VPWRON open, VON2 VUSB VWALLFB unless otherwise noted.
CONDITIONS VPWRON VON2 VMODE VWALLFB 1.35V IPBSTAT 100A IPBSTAT IRST 100A IRST After Regulation
0.02 0.20 0.02 0.20 0.15
UNITS
0.10 0.35 0.10 0.35
With VMAX Rising, VMAX VBAT 3.6V 0.784
0.805 0.826 0.826
VFB2 0.85V 0.6V, 1.5V 0.6V,
0.784
0.805 0.01
VMAX VMODE VFB1 VFB2 0.85V Both Switchers Both Switchers Both Switchers Switcher Switcher From High 3.75
0.35 0.45 3.90
1300 4.10
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LTC3455/LTC3455-1 ELECTRICAL CHARACTERISTICS
PARAMETER Swap Output Swap PMOS Switch On-Resistance Swap PMOS Switch Current Limit HSON Threshold HSON Pulldown Current Battery Charger Regulated Charger VBAT Voltage Charger Current Limit (USB Powered) Charger Current Limit (Wall Powered) Recharge Battery Voltage Threshold Trickle Charge Trip Threshold Trickle Charge Trip Hysteresis Trickle Charge Current PROG Current PROG Voltage CHRG Output Voltage Timer Accuracy Junction Temperature Constant Temperature Mode Note Stresses beyond those listed under Absolute Maximum Ratings cause permanent damage device. Exposure Absolute Maximum Rating condition extended periods affect device reliability lifetime. Note LTC3455/LTC3455-1 guaranteed meet specified performance from 85°C designed, characterized RPROG 2.49k, VBAT Internal Pull-Up Current, RPROG RPROG 2.49k ICHRG CTIMER 0.1F 85°C (LTC3455) 85°C (LTC3455-1) RPROG 2.49k, VUSBHP VUSB 85°C RPROG 2.49k, VUSBHP VUSB 85°C RPROG 2.49k, VMAX 4.5V, 85°C VBAT(REGULATED) VRECHARGE Battery Voltage Rising 4.158 4.058 4.200 2.85 1.23 0.75 4.242 4.142 VHSI 3.3V VHSI 3.3V, VHSO 2.5V CONDITIONS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VBAT 3.6V, VMAX 3.6V, VPWRON open, VON2 VUSB VWALLFB unless otherwise noted.
UNITS
expected meet these extended temperature limits, 100% tested -40°C 85°C. Note Quiescent current pulled from VBAT when neither wall power present, from VMAX when either Wall power present.
TYPICAL PERFORMANCE CHARACTERISTICS
Burst Mode Quiescent Current
QUIESCENT CURRENT VBAT 3.6V SWITCHING TEMPERATURE (°C) BOTH SWITCHERS ENABLED QUIESCENT CURRENT ONLY SWITCHER ENABLED BOTH SWITCHERS ENABLED VBAT 3.6V SWITCHING TEMPERATURE (°C) ONLY SWITCHER ENABLED QUIESCENT CURRENT
Mode Quiescent Current
Shutdown Quiescent Current
VBAT 3.6V
TEMPERATURE (°C)
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LTC3455/LTC3455-1 TYPICAL PERFORMANCE CHARACTERISTICS
Feedback Pins (FB1, FB2) Voltage
SWITCHING FREQUENCY (MHz)
Switching Regulator Oscillator Frequency
1000
Switching Regulator Current Limit
SWITCHER
VOLTAGE (mV)
BOTH SWITCHERS
CURRENT LIMIT (mA)
SWITCHER
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE
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Current Limit
USBHP VMAX CURRENT LIMIT CURRENT (mA) USBHP VUSB TEMPERATURE (°C)
VMAX Current Limit
CURRENT LIMIT (mA) NORMAL OPERATION
Current Limit
STARTUP
VHSI 3.3V VHSO 2.5V TEMPERATURE (°C)
TEMPERATURE (°C)
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Battery Undervoltage Lockout
4.00 3.75 BATTERY UVLO 3.50 3.25 RISING 3.00 2.75 FALLING 2.50 TEMPERATURE (°C) 4.00 3.75
Undervoltage Lockout
1.26 1.24 RISING UVLO 3.50 3.25 3.00 2.75 2.50 FALLING WALLFB TRIP VOLTAGE
WALLFB Trip Voltage
RISING 1.22 1.20 1.18 1.16 1.14 1.12 FALLING
TEMPERATURE (°C)
1.10
TEMPERATURE (°C)
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LTC3455/LTC3455-1 TYPICAL PERFORMANCE CHARACTERISTICS
Battery Charger Regulation Voltage
4.30 4.25 LTC3455 VRECHARGE 4.20 VBAT 4.15 LTC3455-1 4.10 4.05 4.00 4.10 LTC3455 4.05 4.00 LTC3455-1 3.95 3.90 4.20 4.15 TRICKLE CHARGE THRESHOLD
Battery Charger Recharge Threshold
Battery Charger Trickle-Charge Threshold
RISING FALLING
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
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Charge Current When Wall-Powered
BATTERY CHARGE CURRENT (mA) BATTERY CHARGE CURRENT (mA) VBAT 3.6V VMAX 4.5V RPROG 2.49k TEMPERATURE (°C)
Charge Current When USB-Powered
VBAT 3.6V VUSB RPROG 2.49k BATTERY CURRENT VUSBHP THERMAL CONTROL LOOP OPERATION 15.0 12.5 10.0
Battery Current When USB- Wall-Powered
VBAT 4.2V CHARGER
THERMAL CONTROL LOOP OPERATION
VUSBHP
TEMPERATURE (°C)
TEMPERATURE (°C)
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PROG Voltage Charge Current
1.50 VBAT 3.6V VMAX 4.5V 1.25 RPROG 2.49 25°C 1.00 VPROG RDS(ON) 0.75 0.50 0.25
RDS(ON) Switching Regulator Power Switches
VBAT 3.6V
RDS(ON) VMAX, USB, PMOS Switches
VHSI 3.3V VUSB 3.6V
NMOS RDS(ON) PMOS
VMAX
CHARGE CURRENT (mA)
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TEMPERATURE (°C)
TEMPERATURE (°C)
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LTC3455/LTC3455-1 FUNCTIONS
(Pin Feedback Switcher output voltage connecting feedback resistors this pin. PROG (Pin Charge Current Program Charge Current Monitor Pin. Connect resistor, RPROG, from this ground program battery charge current. IBAT 1000 1.23V RPROG modes voltage PROG used measure charge current. PROG weak pull-up current source turn charger left open. TIMER (Pin Timer Capacitor Pin. Connect capacitor, CTIMER, between this ground charge cycle termination time. timer starts when wall power first present. timer period TTIMER (hours) CTIMER hours) (0.1F) TIMER ground disable just internal timer function. TIMER VMAX charger constant-current-only mode (which disables timer, voltage amplifier trickle charge function). CHRG (Pin Open-Drain Charge Status Pin. This pulled with internal N-channel MOSFET whenever battery charger enabled, forced into high impedance state whenever disabled. USBHP (Pin High Power Mode Pin. This used select appropriate current limit (either 500mA 100mA). Pull high select 500mA (high power mode); select 100mA (low power mode). SUSPEND (Pin Suspend Pin. When this pulled high, internal power controller disabled current reduces less than 20A. (Pin Switch Switcher Minimize length metal trace connected this pin. Place inductor Switcher close this possible. (Pin Supply Pin. Input current into this limited either 100mA 500mA based state USBHP pin. charger Switcher will remain alive whenever power present (when above 3.9V SUSPEND low). VBAT (Pin Battery Input Pin. Bypass this with capacitor close device possible. VMAX (Pin 10): Voltage Pin. This used power internal step-down DC/DC converters provided externally power other devices (i.e. LDOs Switchers bias, white backlight drive, etc). When LTC3455/LTC3455-1 neither wall power available, internal PMOS switch connects this VBAT pin. When either wall power present, they provide power this pin, battery charger draws power from this pin. shutdown, this discharged ground provide output disconnect. WALLFB (Pin 11): Wall Power Detection Pin. This input comparator used signal presence wall adapter. resistor divider taken from wall adapter input connected this tell LTC3455/LTC3455-1 when adapter voltage high enough provide power LTC3455/LTC3455-1. When this higher than 1.23V, battery charger enabled. wall adapter connected VMAX through Schottky diode. WALLFB ground wall adapter used. (Pin 12): Switch Switcher Minimize length metal trace connected this pin. Place inductor Switcher close this possible. (Pin 13): Swap Input Pin. This connected through current-limited PMOS switch. (Pin 14): Swap Output Pin. This output used memory cards other devices that would appear short they were hot-plugged directly outputs (typically 3.3V output). current this limited 160mA. HSON (Pin 15): Swap Enable Pin. This turns PMOS that connects pins. (Pin 16): Gain Block Input Pin. This inverting input amplifier that used low-battery detector with addition external PMOS. non-inverting input gain block connected 0.8V internal reference. (Pin 17): Gain Block Output Pin. This opendrain output, pulled when less than 800mV. This output used low-battery detector, with addition external PMOS. This sink 1mA.
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LTC3455/LTC3455-1 FUNCTIONS
(Pin 18): Feedback Switcher output voltage connecting feedback resistors this pin. (Pin 19): Enable Switcher This turns Switcher only PWRON high. Switcher cannot turned itself. (Pin 20): Reset Pin. This open-drain output that provides 200ms reset signal during power-up initialize microcontroller. MODE (Pin 21): Burst Mode Enable Pin. this high allow Burst Mode operation LTC3455/LTC3455-1. Burst Mode operation will provide superior efficiency when both outputs operating with very output currents. this ground force operation under load current conditions. Burst Mode disabled initially startup (for 200ms) also whenever external power available (even MODE pulled high). PWRON (Pin 22): Power-On Pin. Pull this high turn LTC3455/LTC3455-1. This typically used conjunction with PBSTAT pins, momentary-on switch. PWRON ground used. PBSTAT (Pin 23): Push-Button Status Pin. This open drain output that indicates state (which usually connected momentary-on push-button) microcontroller. This follows state (PBSTAT goes when pulled low). (Pin 24): Pin. Pull this ground turn LTC3455/LTC3455-1. This typically used with momentary-on push-button switch turn LTC3455/LTC3455-1. This would held until PWRON pulled high microcontroller keep LTC3455/LTC3455-1 turned momentary-on switch used, this held ground keep LTC3455/LTC3455-1. Leave open used. This weak pull-up current source. (Pin Exposed Pad): Ground Pin. exposed backside only ground LTC3455/ LTC3455-1 must soldered board ground plane device operate properly.
SIMPLIFIED BLOCK DIAGRAM
VMAX CONNECTED BEST AVAILABLE INPUT POWER SOURCE (WALL ADAPTER, BATTERY) POWER 3.9V 5.3V POWER MANAGER WALL ADAPTER
VMAX POWER OTHER DC/DCs LDOs SWITCHER VOUT1 1.8V TYPICAL
Li-Ion BATTERY 3.3V 4.2V
BATTERY PMOS SWITCH
BATTERY CHARGER BATTERY INDICATOR
SWITCHER
VOUT2 3.3V TYPICAL
GAIN BLOCK
SWAP
SWAP OUTPUT 3.3V TYPICAL
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LTC3455/LTC3455-1 BLOCK DIAGRAM
WALL 3.9V POWER MANAGER 5.6V 4.7F BATTERY CHARGER 1000
EXTPWR
3.32k
1.23V
WALLFB 1.24k 4.7F
SUSPEND
1000 BATTERY PMOS SWITCH
VMAX
CONTROLLER
USBHP
VMAX
1.23V 2.41R
VMAX
CHRG TIMER
CHARGE CONTROL
0.1F 2.49k
PROG
SWITCHER DRIVER 4.7H 1.8V
VBAT 3.3V 4.2V 2.43M 4.7F 806k
VBAT
100k 80.6k
0.8V
806k 1.8V ON/OFF
0.8V
ENABLE
SWITCHER VBAT
UVLO
DRIVER
4.7H 3.3V
PBSTAT 806k 1.8V
3.0V 249k EXTPWR 80.6k
200ms RESET PULSE BURST MODE ENABLE SWAP ENABLE
PWRON MODE HSON
ENABLE
0.8V
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3.3V,
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LTC3455/LTC3455-1 OPERATION
LTC3455/LTC3455-1 designed complete power management solution wide variety portable systems. device incorporates current mode stepdown switching regulators, full-featured battery charger, power controller, Swap output, low-battery comparator (which also configured LDO) numerous protection features into single package. When only battery power available, battery PMOS switch connects VMAX VBAT provide power both switching regulators (and other devices powered from VMAX). When external power applied, LTC3455/LTC3455-1 seamlessly transition from battery power single-cell Li-Ion cell) either supply wall adapter. battery PMOS switch turned off, charger activated internal power device drawn from appropriate external power source. Maximum charge current charge time programmed using external resistor capacitor, respectively. power manager provides accurate current limiting under conditions. Swap output ideal powering memory cards other devices that inserted while system fully powered.
APPLICATIONS INFORMATION
Undervoltage Lockout (UVLO) external power present, LTC3455/LTC3455-1 will start only battery voltage above 3.0V. This prevents starting with battery that close deep discharge. Once started, battery must drop below 2.6V before LTC3455/LTC3455-1 will shut off. This hysteresis intentionally large prevent LTC3455/LTC3455-1 from turning inappropriate time, like during read- write-cycle hard-disk drive (which could potentially damage drive). internal UVLO meant only last chance safety measure prevent running battery voltage damaging accurate, user-settable low-battery threshold implemented using gain block (see "Gain Block" section details) which gives microcontroller complete control over timing shutdown low-battery condition. external power present battery voltage less than 3.0V, VMAX voltage must greater than 3.9V LTC3455/LTC3455-1 start, once started, VMAX must stay above 3.1V device continue running. Selecting Input Power Source priority supplying power both DC/DC converters, internal circuitry, VMAX Wall adapter, USB, battery. Whenever WALLFB above 1.23V, system power drawn from wall adapter VMAX pin, battery charger active. wall adapter output connected VMAX through Schottky diode, resistor divider from wall input connected WALLFB signal LTC3455/LTC3455-1 that wall power present. higher voltage adapter also used, maximum rating VMAX requires additional regulator step down voltage. power present above 3.9V (and wall power available), system power drawn from pin. battery charger active, charge current will held until increases above 4.0V prevent battery charger from further loading down already supply. long stays above 3.9V, port supplies other system power. system needs more power than supply, charger turns completely, power controller becomes 500mA 100mA) current source VMAX voltage begins decrease. VMAX continues decrease, eventually battery will provide additional current needed. This allows LTC3455/LTC3455-1 withstand load current transients that briefly require more power than power supply provide.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Operation When Battery Present long wall power available, LTC3455/ LTC3455-1 will operate with battery present, crucial requirement systems with removable battery. Keep mind, however, that LTC3455/LTC3455-1 powered battery present, absence battery means that there reservoir system needs more power than port supply. This especially problem when starting LTC3455/LTC3455-1 power mode with battery present, which discussed greater detail next page, section entitled "Startup Issues Power Mode When Battery Present". Similarly, external power available, LTC3455/LTC3455-1 will operate even battery deep-discharge. LTC3455/LTC3455-1 also good choice systems that always powered supply wall adapter. charger then used charge large capacitor backup battery, which briefly provide power system after external power been removed. This gives microcontroller enough time follow proper shutdown procedures even after main power source abruptly removed. powered, large capacitor backup battery will also used provide additional current system briefly needs more power than provide. Concerns When Wall Adapter Powered Always choose wall adapter that provide power load battery charging requirements. Choosing wall adapter with power rating that small will result very long charge times erratic system operation. total current needed (load battery charging) exceeds what adapter provide, voltage VMAX will begin droop. droops close enough battery voltage (the VBAT pin), charge current decreases eventually reduces zero. load current still much wall adapter provide, wall adapter will provide what battery will provide rest. When wall powered, this operation intended only surviving fault conditions should normal mode operation. Concerns When Powered popularity (Universal Serial Bus) makes attractive choice transferring data variety portable devices. Therefore, utilizing port power these portable devices while charging their battery very desirable, necessarily easy task. performance digital cameras, handheld computers, players increases, power needed operate them also increases. power available from single port (maximum 2.5W) barely enough support peak power needed many full-featured portable devices, even without power needed quickly charge their batteries. further complicate matters, port ideal power source. Each device draw maximum 500mA high power mode), voltage provided portable device vary quite significantly. Although power supply nominal rating, when include normal supply variations, cable losses, transient conditions, voltage showing portable device typically much lower-often falling only Since port strict current limit 500mA, this means amount power available portable device reduced voltage also presents problems when trying fully charge single-cell Lithium-Ion battery when voltage itself below near float voltage. LTC3455/LTC3455-1 specifically designed alleviate these problems make most power port offer. sections entitled "Large Transient Loads when powered" "Special Charger Features when powered" more detailed discussions LTC3455/LTC3455-1's special features.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
High Power/Low Power/Suspend Modes There three basic modes power manager: high power, power, suspend. High power mode allows LTC3455/LTC3455-1 draw 500mA from port, selected pulling USBHP high. power mode reduces allowable current drawn 100mA, selected pulling USBHP low. USBHP weak internal pulldown current source ensure that LTC3455/LTC3455-1 always start power mode. SUSPEND will disable power manager completely, reducing current under 20A. Operation Power Mode Most applications that draw power from should power mode only brief amount time. Devices should power mode (draw more than 100mA current from bus) upon power-up, transition high power mode (draw 500mA from bus) after device been given permission host controller. change high power mode usually very quick, full 500mA current available shortly after connecting bus. While LTC3455/LTC3455-1 will operate when power mode, amount power available small that difficult impossible charge battery even provide enough current power rest system. this reason, high power operation should always used with LTC3455/LTC3455-1. Startup Issues Power Mode When Battery Present applications that must operate power mode when battery present, careful attention must given VMAX output switching regulators loaded, especially during startup. Keep mind that when LTC3455/LTC3455-1 powered battery present, absence battery means that there reservoir system needs more power than port supply. Since only provide 100mA maximum current power mode, this gives, best, only 500mW 100mA) power available everything running. With voltage current limit, less than 300mW available start device. some applications outputs heavily loaded), this simply enough power start system. VMAX switching regulator outputs loaded heavily, LTC3455/LTC3455-1 will unable regulate outputs (due insufficient input power), internal protection circuit will turn part after 200ms. This protection feature discussed detail section entitled "Low Battery Protection (200ms Timeout)". Once this protection circuit tripped, power must removed reapplied restart part. Several steps taken help lighten total system load which will help greatly when LTC3455/LTC3455-1 must start power mode with battery present. Minimize load currents VMAX delaying turn devices that powered from VMAX until after high power mode available. Minimize load current output Switcher since Switcher turns automatically whenever power available. Delay turn-on Switcher until after high power mode available. some applications, high power mode should selected during startup least briefly) allow LTC3455/LTC3455-1 turn properly. Startup high power mode typically problem, more than power available from port this mode.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Handling Large Transient Loads when Powered Many portable devices have nominal loads that easily supported supply, they have brief transient loads that exceed maximum available power. LTC3455/LTC3455-1 designed handle these overloads while drawing much power possible from port. providing power LTC3455/LTC3455-1 other devices connected VMAX pin) need more total power than supply, battery charger turns completely power controller becomes 500mA 100mA) current source VMAX voltage begins decrease. this point, capacitance connected VMAX provides additional current needed system. long stays above 3.9V, will continue provide much current possible. Once VMAX drops just below VBAT voltage, battery will provide additional current needed. This operation allows LTC3455/LTC3455-1 withstand load transients that briefly demand more power than provided bus.
VMAX 2V/DIV IMAX 500mA/DIV IUSB 500mA/DIV IBAT 500mA/DIV 100s/DIV
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oscilloscope photographs Figure show LTC3455/LTC3455-1 handle load transients when powered. photo shows brief transient load that turns charger does VMAX voltage. bottom photo shows prolonged transient condition that turns charger completely dips VMAX voltage point where battery must provide current. both cases, normal operation resumes soon transient passes. Extra capacitance connected VMAX reservoir help support large transient currents. most systems this necessary, LTC3455/LTC3455-1 cleanly handle heavy transients. some designs, however, desirable larger capacitor connected VMAX larger reservoir. ceramic capacitance connected VMAX without difficulty. More than requires using capacitor with some adding some resistance series with some ceramic capacitance. This necessary ensure loop stability battery charger loop when under power.
Maximum Current Condition
VMAX 2V/DIV IMAX 500mA/DIV IUSB 500mA/DIV IBAT 500mA/DIV 100s/DIV
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Heavy Over-Current Condition Figure Handling Load Transients when Powered
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Using VMAX Power Other Devices VMAX used provide power other devices within system. This connected battery when external power available, connected either wall adapter when either available. This ensures that devices powered from VMAX will always draw power from best available input power source. internal PMOS connecting VMAX battery current limited 900mA startup minimize in-rush current) once VMAX risen close battery voltage. Because reduced startup current limit, turn-on other devices powered from VMAX should always delayed minimize currrent initially needed from VMAX pin. best choice enable these devices from either switcher output, since turn-on both switchers always delayed until VMAX reached VBAT voltage. VMAX discharged ground when LTC3455/LTC3455-1 shut down, that device supplied VMAX will have input grounded during shutdown. This ensures output disconnect supply voltages within system. Startup Shutdown when Battery-Powered When only battery power available, LTC3455/ LTC3455-1 turn when either pulled PWRON pulled high. Either these pins will keep device running, typically PWRON pins used together provide turn-on turn-off using single momentary-on push-button switch. Figure shows method using momentary-on pushbutton turn LTC3455/LTC3455-1 When momentary-on switch first pressed, shorting ground, PBSTAT goes LTC3455/LTC3455-1 first bring VMAX pin, then enables Switcher power microcontroller. Once running, microcontroller provides PWRON signal keep LTC3455/LTC3455-1 turned after push-button released. When push-button pressed again turn device, PBSTAT pulled notify microcontroller that push-button been pressed. microcontroller prepares shutdown then pulls PWRON signal low. When push-button released, goes high LTC3455/LTC3455-1 turn off. PWRON pins enable Switcher (along with internal circuits needed normal operation), enables Switcher Switcher only operate when Switcher also enabled. turn-on both switchers always delayed until VMAX reached VBAT voltage.
LTC3455/LTC3455-1 PBSTAT PUSH BUTTON SWITCHER ENABLED SWITCHER ENABLED
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PWRON
Figure Momentary Push-Button Operation
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
PBSTAT PWRON VBAT SWITCHER ENABLED LTC3455/LTC3455-1
SWITCHER ENABLED
WALLFB
CHARGER ENABLED
1.23V
3.9V
POWER CONTROLLER ENABLED
SUSPEND
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Figure Turn-On Logic Diagram
Startup Shutdown When Wall Powered Whenever wall power present sensed WALLFB pins), Switcher battery charger will always enabled. LTC3455/LTC3455-1 external power applied, both charger Switcher will start independent state PWRON pins. This provides maximum battery run-time always allowing battery charge whenever external power available, ensures that microcontroller always alive when external power available (this important designs that utilize coulomb-counting other battery monitoring techniques). Switcher starts only also pulled high. Figure shows turn-on logic diagram LTC3455/LTC3455-1. Starting Switcher 2/Power Supply Sequencing Switcher operate only when Switcher also enabled regulation. driven logic signal independent control Switcher both outputs always operate together, VMAX pin. This will enable Switcher after output Switcher reached final value. This power-up delay ensures proper supply sequencing reduces peak battery current startup. Figure shows
output sequencing when both switchers enabled startup with tied VMAX. turn-on both switchers always delayed until VMAX reached VBAT voltage. Reset Signal (RST) 200ms reset signal (the pulled low) provided proper initialization microcontroller whenever LTC3455/LTC3455-1 first turned either pins, application external power. signal also pulled whenever entire LTC3455/ LTC3455-1 shutdown, ensuring false starts microcontroller output voltages rising collapsing.
PWRON/ON2 2V/DIV VMAX 2V/DIV VOUT1 (1.8V) 2V/DIV VOUT2 (3.3V) 2V/DIV 100s/DIV
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Figure Sequencing Switcher Outputs
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Battery Protection (200ms Timeout) 200ms reset timer also used prevent starting LTC3455/LTC3455-1 when there insufficient external power insufficient battery voltage regulate outputs. When first turned internal 200ms timer starts. only Switcher enabled (ON2 low) output does reach final value within 200ms, Switcher shut down even held PWRON held high (the VMAX will remain long PWRON high). This automatic shutdown feature prevents possible damage defective overdischarged Li-Ion battery. tied VMAX that Switcher also turned startup, then both outputs must reach their final values within 200ms. Once output(s) regulation, timer reset full 200ms. Schottky Diode Selection/WALLFB Resistor Selection When wall adapter used, power provided VMAX through Schottky diode. most important specification picking this diode reverse leakage current. When LTC3455/LTC3455-1 turned wall power present, Schottky will leak current ground through WALLFB resistor divider (see Figure This leakage current should minimized picking appropriate low-leakage Schottky diode) dramatically reduce Burst Mode efficiency light loads. addition, high leakage current also false trip WALLFB turn LTC3455/LTC3455-1 even wall power available. help prevent this false turnon, WALLFB resistor values shown Figure diode forward voltage drop should around 500mV less maximum rated current allow charging even when wall adapter voltage lower than normal. Some manufacturers have recently introduced Schottky diodes optimized very forward drop, their reverse leakage currents more than 100A room temperature, over high temperatures. These diodes recommended with LTC3455/LTC3455-1, they used operation high temperature should checked thoroughly avoid problems excessive diode leakage current. Three good diode choices MBRM110E (1A, 10V), MBR120ESF (1A, 20V), MBRA210E (2A, 10V). available very small packages from Semiconductor (www.onsemi.com), have reverse leakage currents under room temperature, have forward drops around 500mV their maximum rated current 2A).
VMAX VMAX LTC3455/ LTC3455-1 WALLFB 1.24K
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ILEAKAGE 3.32K
WALL
Figure Schottky Leakage Current Path
Switching Regulator General Information LTC3455/LTC3455-1 contain 1.5MHz constantfrequency current mode switching regulators that operate with efficiencies 96%. Switcher provides 400mA 1.5V/1.8V power microcontroller core), Switcher provides 500mA 3V/3.3V power microcontroller I/O, memory other logic circuitry). Both converters support 100% duty cycle operation (low dropout mode) when input voltage drops very close output voltage, both capable operating Burst Mode operation highest efficiencies light loads (Burst Mode operation selectable). Switcher independent ON/OFF control, operates only when Switcher also enabled regulation. both enabled power-up, Switcher allowed turn only after Switcher reached final value. This power-up delay ensures proper supply sequencing reduces peak battery current startup. output Switcher drops below programmed output voltage, Switcher will turn off. This ensures that problems with core supply will shut down rest system.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Switching Regulator Inductor Selection Many different sizes shapes inductors available from numerous manufacturers. Choosing right inductor from such large selection devices overwhelming, following basic guidelines will make selection process much simpler. maximize efficiency, choose inductor with resistance. Keep mind that most inductors that very thin have very small volume typically have much higher core losses, will give best efficiency. Choose inductor with current rating least times larger than maximum load current ensure that inductor does saturate during normal operation. Table shows several inductors that work well with LTC3455/LTC3455-1. These inductors offer good compromise current rating, physical size. Consult each manufacturer detailed information their entire selection inductors.
Table Recommended Inductors
Inductor Type DB318C 0.86 0.58 0.75 0.55 1.29 0.82 0.68 0.18 0.19 0.37 0.11 0.21 0.12 0.28 0.36 Height (mm)
Switching Regulator Output Capacitor Selection (equivalent series resistance) ceramic capacitors should used both switching regulator outputs. Only ceramic capacitors should used because they retain their capacitance over wider voltage temperature ranges than other ceramic types. output capacitor sufficient most applications. Table shows list several ceramic capacitor manufacturers. Consult each manufacturer detailed information their entire selection ceramic capacitors. Many manufacturers offer very thin (<1mm tall) ceramic capacitors ideal height-restricted designs.
Table Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden Murata (408) 573-4150 (803) 448-9411 (714) 852-2001 (888) 835-6646 www.t-yuden.com www.avxcorp.com www.murata.com www.tdk.com
VBAT Capacitor Selection
Manufacturer Toko (847)297-0070 www.toko.com Sumida (847)956-0666 www.sumida.com Sumida Cooper (561)752-5000 www.cooperet.com Panasonic (408)945-5660 www.panasonic.com
VBAT pin, 4.7F ceramic capacitor best choice. Only type ceramic capacitors should used. VMAX Capacitor Selection VMAX pin, ceramic capacitor best choice. Only type ceramic capacitors should used. less than this pin. some designs desirable larger capacitor connected VMAX reservoir when LTC3455/ LTC3455-1 powered. ceramic capacitance connected VMAX without difficulty. More than requires using capacitor with some (like Tantalum OS-CON) adding some resistance series with some ceramic capacitance. This necessary ensure loop stability battery charger loop when under power.
CLS4D09
CDRH3D16 SD12
ELT5KT
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Wall Adapter Capacitor Selection wall adapter inputs should bypassed with 4.7F capacitor. some applications, wall input bypassed locally with lower value (down 1F), only other bulk capacitance present. should always have least 4.7F Ceramic capacitors (only type X7R) typically best choice their small size good surge current ratings, care must taken when they used. When ceramic capacitors used input bypassing, series resistor must added prevent overvoltage ringing that often occurs when these inputs hot-plugged. tantalum, OS-CON, electrolytic capacitor used place ceramic resistor, their higher reduces thus reducing voltage ringing. Protecting Wall Adapter Input from Overvoltage Transients Caution must exercised when using ceramic capacitors bypass wall adapter inputs. High voltage transients generated when wall adapter plugged. When power supplied wall adapter, cable inductance along with self resonant high characteristics ceramic capacitors cause substantial ringing which easily exceed maximum voltage ratings damage LTC3455/LTC3455-1. Refer Linear Technology Application Note entitled "Ceramic Input Capacitors Cause Overvoltage Transients" detailed discussion this problem. long cable lengths most wall adapters cables makes them especially susceptible this problem. bypass wall adapter input, resistor series with ceramic capacitor lower effective network greatly reduce ringing. tantalum, OS-CON, electrolytic capacitor used place ceramic resistor, their higher reduces thus reducing voltage ringing. oscilloscope photograph Figure shows serious overvoltage transient wall adapter inputs. both traces, supply hot-plugged using three foot long cable. trace, only 4.7F capacitor (without recommended
4.7F ONLY 2V/DIV
4.7F 2V/DIV
3455
20s/DIV
Figure Waveforms Resulting from Hot-Plugging Input Supply
series resistor) used locally bypass input. This trace shows excessive ringing when cable inserted, with overvoltage spike reaching 10V; more than enough damage LTC3455/LTC3455-1. bottom trace, resistor added series with 4.7F capacitor locally bypass input. This trace shows clean response resulting from addition resistor. Even with additional resistor, design techniques poor board layout often make overvoltage problem even worse. System designers often extra inductance series with input lines attempt minimize noise back those inputs application. reality, adding these extra inductances only makes overvoltage transients worse. Since cable inductance fundamental causes excessive ringing, adding series ferrite bead inductor increases effective cable inductance, making problem even worse. this reason, additional inductance (ferrite beads inductors) series with wall adapter inputs. most robust solution, transorbs zener diodes also added further protect wall adapter inputs. possible protection devices SM2T from STMicroelectronics series devices from ROHM. Always oscilloscope check voltage waveforms VMAX pins during wall adapter hot-plug events ensure that overvoltage transients have been adequately removed.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Programming Switching Regulator Output Voltage output voltage each switching regulator programmed using resistor divider from output connected feedback pins (FB1 FB2): VOUT Typical values range 400k.
VOUT FB1,
MODE VMAX always allow automatic Burst Mode operation. Even when MODE high, LTC3455/LTC3455-1 will only enter Burst Mode when load current low. many noise-sensitive systems, Burst Mode operation might undesirable certain times (i.e. during transmit receive cycle wireless device), highly desirable others (i.e. when device low-power standby mode). MODE used enable disable Burst Mode operation time, offering both low-noise low-power operation when they needed most. Burst Mode disabled initially startup (for first 200ms) also whenever external power available, even MODE pulled high. Figure shows switching waveforms switcher (both mode Burst Mode Operation) with 3.6V, VOUT1 1.8V, IOUT1 25mA.
Burst Mode
VSW1 2V/DIV VOUT1 50mV/DIV AC-COUPLED
LTC3455/ LTC3455-1
3455
Figure Setting Output Voltage
Burst Mode Operation highest efficiencies light loads, both DC/DC converters capable operating Burst Mode. this mode, energy delivered outputs shorts bursts, which minimizes switching losses quiescent-current losses. Output voltage ripple slightly higher this mode, efficiency greatly improved. shown Figure efficiency load currents increases significantly when Burst Mode operation used.
EFFICIENCY VBAT 3.6V LOAD CURRENT (mA) 1000
3455
100mA/DIV 5s/DIV
3455 F09a
Mode
Burst Mode 3.3V VSW1 2V/DIV 3.3V Mode VOUT1 10mV/DIV AC-COUPLED
1.8V Burst Mode
1.8V Mode
100mA/DIV 1s/DIV
3455 F09b
Figure Burst Mode Mode Waveforms
Figure Burst Mode Efficiency
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Soft-start accomplished gradually increasing peak inductor current each switcher. This allows each output rise slowly, helping minimize battery in-rush current. Figure shows battery current during startup. soft-start cycle occurs whenever each switcher first turns after fault condition occurred (thermal shutdown UVLO). In-Rush Current Limiting When LTC3455/LTC3455-1 battery-powered, internal 0.15 PMOS switch connects battery (VBAT pin) VMAX provide power both switchers other internal circuitry. This PMOS switch turned shutdown, VMAX discharges ground, providing output disconnect outputs. startup, this PMOS must first charge capacitance present VMAX battery voltage. minimize inrush current needed from battery, PMOS switch current-limited 900mA both switchers disabled while VMAX voltage ramping Once VMAX reaches battery voltage, PMOS current-limit increases both switchers allowed turn Figure shows startup battery current LTC3455/LTC3455-1, which stays well-controlled while VMAX ramping while both switchers outputs rising. Battery Charger General Information battery charger Switcher will always enabled whenever wall power present sensed WALLFB pins). This ensures that battery charged that microcontroller alive whenever external power available. some applications, undesirable charger become active immediately when external power applied. such applications, NMOS switch used disconnect RPROG resistor allow PROG float high, turning charger. this manner, charging occurs only when allowed microcontroller. LTC3455/LTC3455-1 battery chargers constantcurrent, constant-voltage chargers. constant-current mode, maximum charge current single external resistor. When battery approaches final float voltage, charge current begins decrease charger switches constant-voltage mode. charge cycle terminated only charge timer. Charge Recharge Cycles When external power first applied, charge cycle always initiated. battery will continue charging until programmed charge time reached. battery voltage below 4.05V this cycle, LTC3455/LTC3455-1 will start charge cycle. This action will continue until battery voltage exceeds 4.05V threshold. This operation typically seen only when charging from power. Because charge current vary dramatically when LTC3455/LTC3455-1 powered, takes considerably longer charge battery using supply compared wall adapter). timer capacitor chosen correctly, battery should fully charged cycle when wall power available. battery above 4.05V threshold when charge cycle expired, charging will stop. this point, recharge cycle initiated following occurs: battery voltage drops below 4.05V, external power removed reapplied, PROG floated temporarily, SUSPEND temporarily pulled high LTC3455/LTC3455-1 under power).
VMAX 2V/DIV VOUT1 (1.8V) 2V/DIV VOUT2 (3.3V) 2V/DIV IBAT 500mA/DIV 100s/DIV
3455
Figure In-Rush Current Start-Up
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Programming Charge Current maximum charge current programmed using external resistor connected between PROG (use closest resistor value): RPROG 1000 1.23V IBAT only power used wall adapter), select RPROG value 2.49k larger) maximum charge current 500mA. wall adapter also used, ICHARGE programmed (with 1.24k RPROG value), power manager will automatically throttle back charge current below 500mA when under power. Monitoring Charge Current voltage PROG accurate indication battery charge current under charging conditions. IBAT 1000 VPROG RPROG Capacitance PROG should minimized ensure loop stability when constant-current mode. place capacitor directly from PROG ground. Adding external network (see Figure allows monitoring average, rather than instantaneous, battery charge current. Average charge current typically more interest user, especially when LTC3455/LTC3455-1 powered, battery charge current varies significantly with normal load transients.
LTC3455/ LTC3455-1 PROG RPROG CFILTER
CHRG assumes high impedance state. total charge time programmed TTIMER (hours) CTIMER hours) (0.1F) most applications, three hour timer will provide sufficient time completely recharge battery. some applications with larger capacity batteries, four five hours charging needed. potential problem arises with setting such long timer periods (longer than hours): battery just below recharge threshold (meaning almost fully charged) will still charged total timer period when external power applied. This means that battery will continually charged very, very charge current full four five hours, even battery reaches float voltage right away. This type charging undesirable some battery applications, avoided choosing shorter timer period (but less than hour). charge cycle, LTC3455 will measure battery voltage above 4.05V recharge threshold. above 4.05V, charge cycle will begin, repeating until battery voltage above 4.05V. Even battery charges just above 4.05V threshold using this shorter timer method, more than charge capacity should easily reached (Note: LTC3455-1 recharge threshold 3.95V instead 4.05V). Trickle Charge Defective Battery Detection battery voltage below 2.85V beginning charge cycle, charger goes into trickle charge mode, reducing charge current programmed full-scale value. battery voltage remains quarter programmed total charge time, battery assumed defective, charge cycle terminated, CHRG goes high impedance state. This fault cleared following occurs: battery voltage rises above 2.85V, external power removed reapplied, PROG floated temporarily, SUSPEND temporarily pulled high LTC3455/LTC3455-1 under power). device will still operate normally from wall power even charger turned trickle-charge timeout.
CHARGE CURRENT MONITOR CIRCUITRY
3455
Figure Monitoring Average Charge Current
Programming Battery Charger Timer external capacitor TIMER sets total charge time. When this timer elapses charge cycle terminates
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
Battery Charger Thermal Limit internal thermal limit reduces charge current temperature attempts rise above approximately 105°C. This protects LTC3455/LTC3455-1 from excessive temperature, allows user push limits power handling capability given circuit board without risk damaging LTC3455/LTC3455-1. Another benefit thermal limit that charge current according typical, worst-case, ambient temperatures given application with assurance that charger will automatically reduce current under worst-case conditions. CHRG Status Output CHRG pulled with internal N-channel MOSFET whenever battery charger enabled, forced into high impedance state whenever disabled. This NMOS device capable driving external LED. This does provide C/10 information. Special Charger Features while Powered LTC3455/LTC3455-1 have several special features that help make most power available from power supply. internal power controller automatically throttles back battery charge current help keep total system current under strict 500mA/100mA limit. graph Figure shows charge current, IBAT, decreases current needed rest system increases (both switchers other external devices pull current from VMAX pin). total current, IUSB, always stays below 500mA. voltage drops below 4.5V, charge current gradually reduces (and eventually shuts around 4V). This helps prevent "chattering" stability problems when using long, resistive cables. Figure shows this reduction charge current.
HIGH POWER MODE VBAT 3.6V IBAT CHARGE CURRENT (mA) IBAT IUSB
HIGH POWER MODE VUSB VBAT 3.6V -100 TOTAL SYSTEM CURRENT (mA)
3455
Figure Charge Current Total System Current
CHARGE CURRENT (mA)
3.75
4.00
4.25
4.50 4.75 VUSB
5.00
5.25
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Figure Charge Current Voltage
Because charge current vary dramatically when LTC3455/LTC3455-1 powered, battery charging take considerably longer using supply compared wall adapter). Constant-Current-Only Charger/Disabling Charger Timer charger constant-current-only mode, connect TIMER VMAX disable timer, voltage amplifier, trickle charge function. disable only timer function leave others intact, connect TIMER
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
GND. Since charge cycle terminated only charge timer, external charge termination required when using either these methods. external NMOS float PROG disable charging. Constant-current-only mode good choice systems that always powered supply wall adapter, charger used charge super-cap backup battery. Disabling voltage amplifier allows super-cap/backup battery charge fully available wall adapter voltage. Swap Output current limited Swap output provided powering memory cards other external devices that hot-plugged into system. Typically connected 3.3V supply, this output provides isolation prevent external device from disturbing 3.3V supply when inserted. Swap output only operate when LTC3455/LTC3455-1 enabled using HSON pin. this hot-plugging protection needed, this output used load switch other devices within system. discharged ground when LTC3455/LTC3455-1 shut down. Gain Block LTC3455/LTC3455-1 contain gain block (pins that used either low-battery indicator, with addition external Both circuits shown Figure convenient applications needing third output (possibly current 2.5V quiet supply). sink around 1mA, which typically limits current 100mA less (due current gain PNP). external PMOS used LDO, much larger output capacitor needed ensure stability light loads.
LOW-BATTERY DECTECTOR 1.8V VBAT 2.49M 806k LTC3455/ LTC3455-1 2.5V 169k 80.6k
3455
3.3V 100k
100pF LTC3455/ LTC3455-1
Figure Low-Battery Detector Using Gain Block
gain block alive whenever switcher enabled, turned during shutdown minimize battery drain. This means that low-battery detector will report low-battery condition until LTC3455/LTC3455-1 turned This problem most applications since LTC3455/LTC3455-1 usually power microcontroller other intelligence system. Layout Considerations with DC/DC converters, careful attention must paid printed circuit board (PCB) layout component placement. VBAT capacitor, VMAX capacitor, both inductors must placed close possible LTC3455/LTC3455-1. These components, along with both DC/DC converter output capacitors, should placed same side circuit board LTC3455/LTC3455-1, with their connections made that layer. Place local, unbroken ground plane below these components that tied Exposed LTC3455/LTC3455-1. Exposed (pin must soldered system ground) proper operation. Figure shows recommended placement power sections LTC3455/LTC3455-1.
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LTC3455/LTC3455-1 APPLICATIONS INFORMATION
VOUT1
VOUT2
VBAT VIAS LOCAL GROUND PLANE. VMAX WALL ADAPTER
Figure Recommended Board Layout Component Placement Power Sections LTC3455/LTC3455-1 (Refer Schematic Back Page)
Standalone Power Supply with Temporary Backup Power Although designed primarily Li-Ion powered portable applications, LTC3455/LTC3455-1 also good choices systems that always powered supply wall adapter. battery charger then used charge large capacitor backup battery, which briefly provides power system after external power been removed. This gives microcontroller enough time follow proper shutdown procedures when main power source abruptly removed. Figure shows standalone power supply high power applications (500mA maximum current) using LTC3455/LTC3455-1. total system power should kept below 1.8W ensure clean operation even under worst-case conditions. With resistor values
shown, low-battery indicator pins) triggers when VMAX voltage drops notifying microcontroller impending dropout condition. resistor connected between pins provides 150mV hysteresis (the dropout indicator stays until VMAX rises back above 4.15V). 4700F backup capacitor connected VBAT briefly provides power system after supply been removed, also helps support transient loads that slightly exceed current limit. Connecting this large capacitance VBAT several advantages. provides large energy reservoir that isolated from both (the specification limits capacitance supply less) VMAX (using very large capacitance this will delay system turn-on), prevents large inrush currents
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LTC3455/LTC3455-1 TYPICAL APPLICATIONS
using battery charger slowly charge this capacitor (normally using such large capacitor would result very large inrush currents). With TIMER tied VMAX, battery charger operates constant-current mode (the voltage-loop timer function disabled), 4700F capacitor always fully charged available voltage.
MODE HSON PWRON VMAX PBSTAT LTC3455/LTC3455-1 4700F 1.8V DROPOUT VMAX 82.5k
3455
4.7F 5.6V CONTROLLER
SUSPEND USBHP
1.8V ON/OFF 3.3V,
CHRG WALLFB TIMER PROG VBAT
VMAX 2.49k
4.7H 10pF 249k 80.6k 4.7H 10pF 100k 80.6k 1.8V 0.2A 3.3V 0.4A
CERAMIC TOKO DB318C RESISTORS
Figure Standalone Power Supply with Temporary Backup Power
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LTC3455/LTC3455-1 TYPICAL APPLICATIONS
4.7F 5.6V CONTROLLER SUSPEND USBHP MODE HSON PWRON VMAX PBSTAT 0.1F 1.24k 2.49k SINGLE CELL Li-ION 3.3V 4.2V 4.7F VBAT TIMER PROG 4.7H 100pF LTC3455/LTC3455-1 CHRG WALLFB ON/OFF 3.3V, 1.8V
WALL 4.7F 3.32k
VMAX FDN304P Si2305DS 3.3V 1.2A 2x10F 2.49k
249k
80.6k 4.7H 10pF 100k 80.6k 1.8V 0.4A
CERAMIC TOKO DB318C SEMI MBRM110E RESISTORS
3455
Figure LTC3455/LTC3455-1 Application with 3.3V Output Current Increased 1.2A
Increasing 3.3V Output Current 1.2A With internal current limit 900mA, Switcher typically provides 3.3V, 600mA output. While this output current sufficient many portable devices, some applications need 3.3V supply capable providing more than Figure shows implement higher current 3.3V output using LTC3455/LTC3455-1. adding tiny SOT23 PMOS using AI/AO amplifier LDO, 3.3V output provides 1.2A output current. Switcher programmed output voltage 3.3V, programmed output voltage 3.2V lower). long load current enough Switcher provide, turned completely. This circuit ideal applications that need higher 3.3V output current only brief time. Switcher will normally provide output current, will turn briefly provide higher load currents.
When load current exceeds what Switcher provide, 3.3V output droops slightly provides additional current needed. Figure shows transient response when 3.3V output current stepped from 0.5A 1.2A. More output capacitance added improve 3.3V transient response during these high current load steps.
VOUT2 (3.3V) 100mV/DIV AC-COUPLED IOUT2 0.5A/DIV 0.5A STEP GATE 2V/DIV 500s/DIV
3455
Figure Load Current Step (0.5A 1.2A) 3.3V Output
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LTC3455/LTC3455-1 PACKAGE DESCRIPTION
Package 24-Lead Plastic (4mm 4mm)
(Reference 05-08-1697)
0.70 ±0.05
4.50 0.05 2.45 0.05 3.10 0.05 SIDES)
PACKAGE OUTLINE 0.25 ±0.05 0.50 RECOMMENDED SOLDER PITCH DIMENSIONS 0.75 0.05 BOTTOM VIEW-EXPOSED 0.115 NOTCH 0.20 0.35 CHAMFER
4.00 0.10 SIDES) MARK (NOTE
0.40 0.10
2.45 0.10 (4-SIDES)
(UF24) 0105
0.200 0.00 0.05 NOTE: DRAWING PROPOSED MADE JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)-TO APPROVED DRAWING SCALE DIMENSIONS MILLIMETERS DIMENSIONS EXPOSED BOTTOM PACKAGE INCLUDE MOLD FLASH. MOLD FLASH, PRESENT, SHALL EXCEED 0.15mm SIDE, PRESENT EXPOSED SHALL SOLDER PLATED SHADED AREA ONLY REFERENCE LOCATION BOTTOM PACKAGE
0.25 0.05 0.50
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Information furnished Linear Technology Corporation believed accurate reliable. However, responsibility assumed use. Linear Technology Corporation makes representation that interconnection circuits described herein will infringe existing patent rights.
LTC3455/LTC3455-1 TYPICAL APPLICATION
4.7F 5.6V CONTROLLER SUSPEND USBHP MODE HSON PWRON VMAX PBSTAT REMOVE THESE COMPONENTS WALL ADAPTER USED 0.1F 1.24k 2.49k SINGLE CELL Li-ION 3.3V 4.2V 4.7F 1.8V VBAT 2.49M 806k
3455 TA03
WALL 4.7F 3.32k
1.8V ON/OFF 3.3V,
LTC3455/LTC3455-1 CHRG WALLFB TIMER PROG VBAT 4.7H 10pF
249k 80.6k
3.3V 0.5A
4.7H 10pF 100k 80.6k 1.8V 0.4A
CERAMIC TOKO DB318C SEMI MBRM110E RESISTORS
RELATED PARTS
PART NUMBER LT1616 LTC1879 LTC3405/LTC3405A LTC3406/LTC3406B LTC3407 LTC3412 LTC3414 LTC3440/LTC3441 DESCRIPTION 500mA (IOUT), 1.4MHz, High Efficiency Step-Down DC/DC Converter 1.2A (IOUT), 550kHz, Synchronous Step-Down DC/DC Converter 300mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter Dual 600mA (IOUT), 1.5MHz, Synchronous Step-Down DC/DC Converter 2.5A (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter (IOUT), 4MHz, Synchronous Step-Down DC/DC Converter 600mA/1A (IOUT), 2MHz/1MHz, Synchronous Buck-Boost DC/DC Converter COMMENTS Efficiency, VIN: 3.6V 25V, VOUT(MIN) 1.25V, 1.9mA, <1A, ThinSOT Efficiency, VIN: 2.7V 10V, VOUT(MIN) 0.8V, 15A, <1A, TSSOP16 Efficiency, VIN: 2.7V VOUT(MIN) 0.8V, 20A, <1A, ThinSOT Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 20A, <1A, ThinSOT Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 40A, <1A, MS10E Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 0.8V, 60A, <1A, TSSOP16E Efficiency, VIN: 2.25V 5.5V, VOUT(MIN) 0.8V, 64A, <1A, TSSOP16E Efficiency, VIN: 2.5V 5.5V, VOUT(MIN) 2.5V, 25A/50A, <1A, MS/DFN
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Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
0708 PRINTED
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2006

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