LT3501 Monolithic Dual Tracking Step-Down Switching Regulator DESCRIPT
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LT3501 Monolithic Dual Tracking Step-Down Switching Regulator DESCRIPTION
LT®3501 dual current mode step-down DC/DC converter with internal 3.5A switches. Independent input voltage, feedback, soft-start power good pins each channel simplify complex power supply tracking/sequencing requirements. Both converters synchronized either common external clock input resistor programmable fixed 250kHz 1.5MHz internal oscillator. frequencies, 180° phase relationship between channels maintained, reducing voltage ripple component size. Programmable frequency allows optimization between efficiency external component size. Minimum input-to-output voltage ratios improved allowing switch stay through multiple clock cycles, only switching when boost capacitor needs recharging, resulting ~95% maximum duty cycle. Each output independently disabled using soft-start pin, using SHDN entire part placed quiescent current shutdown mode. LT3501 available 20-lead TSSOP package with exposed leadframe thermal resistance.
LTC, Lare registered trademarks Linear Technology Corporation. other trademarks property their respective owners.
Wide Input Range: 3.1V Switching Regulators with Output Capability Independent Supply Each Regulator Adjustable/Synchronizable Fixed Frequency Operation from 250kHz 1.5MHz Antiphase Switching Outputs Paralleled Independent, Sequential, Ratiometric Absolute Tracking Between Outputs Independent Soft-Start Power Good Pins Enhanced Short-Circuit Protection Dropout: Maximum Duty Cycle Shutdown Current: <10µA 20-Lead TSSOP Package with Exposed Leadframe
APPLICATIONS
Power Supplies Disc Drives DSL/Cable Modems Wall Transformer Regulation Distributed Power Regulation
TYPICAL APPLICATION
3.3V 1.8V Dual Step-Down Converter with Output Tracking
Efficiency
4.7µF VIN1 SHDN 4.7µH BST1 0.47µF LT3501 IND1 VOUT1 47µF 24.9k IND2 VOUT2 B360A VOUT2 1.8V 100µF B360A VIN2 RT/SYNC BST2 0.47µF 61.9k
VOUT1 VOUT1 3.3V
3.3µH
EFFICIENCY
IOUT2 FREQUENCY 500kHz LOAD CURRENT VOUT1 1.8V VOUT1 2.5V
PMEG4005 VOUT1 3.3V
PMEG4005
470pF 8.06k 10pF 40.2k
SS/TRACK1 SS/TRACK2 0.1µF
470pF 40.2k 47pF 8.06k
3501 TA01a
3501 TA01b
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LT3501 ABSOLUTE MAXIMUM RATINGS
(Note
PACKAGE/ORDER INFORMATION
VIEW VIN1 IND1 VOUT1 VOUT2 IND2 BST1 SS/TRACK1 RT/SYNC SHDN SS/TRACK2 BST2
VIN1/2, SHDN, PG1/2 25V/-0.3V SW1/2 .VIN1/2 BST1/2 35V/-0.3V BST1/2 Pins Above SW1/2.25V IND1/2 .±5A VOUT1/2 VIN1/2/-0.3V FB1/2, SS1/2, RT/SYNC .5.5V VC1/2 .±1mA Operating Junction Temperature Range LT3501EFE (Notes -40°C 125°C LT3501IFE (Notes -40°C 125°C Storage Temperature Range. -65°C 150°C Lead Temperature (Soldering, sec) 300°C
VIN2
PACKAGE 20-LEAD PLASTIC TSSOP TJMAX 125°C, 45°C/W, JC(PAD) 10°C/W EXPOSED (PIN GND, MUST SOLDERED
ORDER PART NUMBER LT3501EFE LT3501IFE
Order Options Tape Reel: Lead Free: #PBF Lead Free Tape Reel: #TRPBF Lead Free Part Marking: http://www.linear.com/leadfree/ Consult Marketing parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
PARAMETER SHDN Threshold SHDN Input Current Minimum Input Voltage (Note Minimum Input Voltage Supply Shutdown Current Supply Shutdown Current Supply Quiescent Current Supply Quiescent Current Feedback Voltage Feedback Voltage Line Regulation Feedback Voltage Offset Feedback Bias Current Error Amplifier Error Amplifier Gain Error Amplifier Switch Gain CONDITIONS
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VVIN1/2 15V, VBST1/2 open, VRT/SYNC VVOUT1/2 open, unless otherwise specified.
1.28
1.37 0.816
UNITS µmho
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VOUT1/2 RT/SYNC 133k VSHDN 1.375V VSHDN 1.225V VFB1/2 VVOUT1/2 VIND1/2 RT/SYNC 133k VFB1/2 VVOUT1/2 VIND1/2 VSHDN VSHDN VFB1/2 0.9V VFB1/2 0.9V VVC1/2 VVIN1/2 VVC1/2 VFB1/2 0.8V, VVC1/2 VVC1/2 IVC1/2 ±5µA
1.23
0.784 -250
1000
LT3501 ELECTRICAL CHARACTERISTICS
PARAMETER Error Amplifier Source Current Error Amplifier Sink Current Error Amplifier High Clamp Error Amplifier Switching Threshold Soft-Start Source Current Soft-Start Soft-Start Sink Current Soft-Start Soft-Start Feedback Offset Soft-Start Sink Current Soft-Start Threshold Soft-Start Switching Threshold Power Good Leakage Power Good Threshold Power Good Hysteresis Power Good Sink Current Power Good Shutdown Sink Current RT/SYNC Reference Voltage Switching Frequency Switching Phase Angle Minimum Boost 100% Duty Cycle SYNC Frequency Range SYNC Switching Phase Angle VOUT Current VOUT Maximum Current Switch Leakage Current Switch Saturation Voltage Boost Current Minimum Boost Voltage CONDITIONS VFB1/2 0.6V, VVC1/2 VFB1/2 VVC1/2 VFB1/2 0.7V VOUT1/2 RT/SYNC 133k VFB1/2 0.6V, VSS1/2 0.4V VFB1/2 0.9V VFB1/2 0.6V, VSS1/2 VFB1/2 VVC1/2 VSS1/2 0.4V VSS1/2 0.4V (Note VFB1/2 (Note VFB1/2 VFB1/2 0.9V, VPG1/2 25V, VVIN1/2 VFB1/2 Rising, PG1/2 VFB1/2 Falling, PG1/2 VFB1/2 0.65V, VPG1/2 0.4V VVIN1/2 VFB1/2 VPG1/2 0.4V VFB1/2 0.9V, IRT/SYNC -40µA RT/SYNC 133k, VFB1/2 0.6V, VBST1/2 RT/SYNC 15.4k, VFB1/2 0.6V, VBST1/2 RT/SYNC 133k, VFB1/2 0.6V, VBST1/2 VFB1/2 0.7V, IRT/SYNC -35µA (Note VOUT VBST1/2 SYNC Frequency 250kHz, VBST1/2 VVOUT1/2 VFB1/2 0.9V VVOUT1/2 VVOUT1/2 0.5V (Note VFB1/2 0.7V, VBST1/2 VVOUT1/2 (Note RT/SYNC 133k, VBST1/2 VSW1/2 VVIN1/2 ISW1/2 VBST1/2 20V, VFB1/2 0.7V ISW1/2 VBST1/2 20V, VFB1/2 0.7V ISW1/2 VBST1/2 20V, VFB1/2 0.7V
denotes specifications which apply over full operating temperature range, otherwise specifications 25°C. VVIN1/2 15V, VBST1/2 open, VRT/SYNC VVOUT1/2 open, unless otherwise specified.
1.75 0.93 3.25 3.25 0.975 2.25 1000 1200 1500 UNITS
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 LT3501EFE guaranteed meet performance specifications from 125°C junction temperature. Specifications over -40°C 125°C operating junction temperature range assured design, characterization correlation with statistical process controls. LT3501IFE guaranteed tested over full -40°C 125°C operating junction temperature range. Note Minimum input voltage defined voltage where internal bias lines regulated that reference voltage oscillator remain
constant. Actual minimum input voltage maintain regulated output will depend upon output voltage load current. Applications Information. Note internal power-on reset (POR) latch positive transition SHDN through threshold. output latch activates current sources each which typically sink 1.5mA, discharging capacitor. latch reset when both pins driven below soft-start threshold SHDN taken below threshold. Note enhance dropout operation, output switch will turned minimum time only when voltage across boost capacitor drops below minimum boost 100% duty cycle threshold.
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LT3501 ELECTRICAL CHARACTERISTICS
Note VOUT maximum current defined value current flowing from VOUT which resets switch latch when high clamp. Note This minimum voltage across boost capacitor needed guarantee full saturation internal power switch. Note This includes overtemperature protection that intended protect device during momentary overload conditions. Junction temperature will exceed 125°C when overtemperature protection active. Continuous operation above specified maximum operating junction temperature impair device reliability.
TYPICAL PERFORMANCE CHARACTERISTICS
Feedback Voltage Temperature
0.816 0.811 0.806 0.801 0.796 0.791 0.786 0.97 1.05
RT/SYNC Voltage Temperature
Shutdown Threshold Minimum Input Voltage Temperature
1.03 VOLTAGE
MINIMUM INPUT VOLTAGE SHUTDOWN THRESHOLD VOLTAGE
VOLTAGE
1.01
0.99
TEMPERATURE (°C)
0.95
VOLTAGE TEMPERATURE (°C)
TEMPERATURE (°C)
3501
3501
3501
Shutdown Quiescent Current Temperature
CURRENT (µA) VVIN2 TEMPERATURE (°C) VVIN1 CURRENT (µA)
Soft-Start Source Current Temperature
CURRENT TEMPERATURE (°C)
VOUT Maximum Current Temperature
VOUT VOUT
TEMPERATURE (°C)
3501
3501
3501
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LT3501 TYPICAL PERFORMANCE CHARACTERISTICS
Soft-Start Feedback Offset Voltage Temperature
VOLTAGE (mV) VOUT VOLTAGE TEMPERATURE (°C) VOLTAGE VOUT TEMPERATURE (°C) TEMPERATURE (°C) RISING FALLING 1000
Switching Threshold Voltage Temperature
Power Good Threshold Voltage Temperature
3501
3501
3501
Power Good Sink Current Temperature
1000 CURRENT (µA) TIME (ns) TEMPERATURE (°C)
Minimum Switching Times Temperature
MINIMUM TIME FREQUENCY (kHz) TEMPERATURE (°C)
Switching Frequency Channel Phase Temperature
RT/SYNC 133k PHASE PHASE (DEG) FREQUENCY TEMPERATURE (°C)
MINIMUM TIME
3501
3501
3501
Switching Frequency Channel Phase Temperature
1650 1600 FREQUENCY (kHz) 1550 FREQUENCY 1500 1450 1400 1350 RRT/SYNC 15.4k PHASE FREQUENCY (kHz) PHASE (DEG) TEMPERATURE (°C) 2000 2500
Syncronization Clock Frequency Range Temperature
PHASE (DEG) MAXIMUM SYNCHRONIZATION FREQUENCY MINIMUM SYNCHRONIZATION FREQUENCY TEMPERATURE (°C)
Channel Phase Temperature with External Synchronization
1500
SYNCHRONIZATION FREQUENCY 250kHz
1000
SYNCHRONIZATION FREQUENCY 1500kHz TEMPERATURE (°C)
3501
3501
3501
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LT3501 TYPICAL PERFORMANCE CHARACTERISTICS
External Sync Duty Cycle Range External Sync Frequency
DUTY CYCLE 1000 1250 FREQUENCY (kHz) 1500
3501
Frequency Phase RT/SYNC Resistance
1600 1400 FREQUENCY 1200 FREQUENCY (kHz) 1000 RESISTANCE
1344
Switch Saturation Voltage Switch Current
125°C VOLTAGE (mV) CURRENT
3501
MAXIMUM CLOCK DUTY CYCLE
PHASE (DEG) PHASE
25°C
-50°C
MINIMUM CLOCK DUTY CYCLE
Minimum Boost Voltage Temperature
CURRENT (µA) VOLTAGE TEMPERATURE (°C)
VOUT Current Temperature
CURRENT (µA) TEMPERATURE (°C)
VOUT Current Voltage
VOLTAGE
3501
3501
3501
Minimum Input Voltage Load Current
1000 CURRENT (mA) 10000
3501
Minimum Input Voltage Load Current
VOUT 3.3V RUNNING 1000 CURRENT (mA) 10000
3501
Minimum Input Voltage Load Current
VOUT
VOUT 2.5V
VOLTAGE
VOLTAGE
VOLTAGE
RUNNING
RUNNING 1000 CURRENT (mA) 10000
3501
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LT3501 TYPICAL PERFORMANCE CHARACTERISTICS
Dropout Operation
OUTPUT VOLTAGE VOUT FREQUENCY (kHz) FREQUENCY 1.5MHz 250kHz INPUT VOLTAGE VOUT 3.3V 1000 LOAD 1500
Inductor Value Frequency Maximum Load Current
VOUT 3.3V IRIPPLE 2.2µH FREQUENCY (kHz) 1500
Inductor Value Frequency Maximum Load Current
2.2µH 1250 3.3µH 1000 4.7µH 6.8µH 10µH VOUT IRIPPLE
1250
3.3µH
4.7µH 6.8µH
INPUT VOLTAGE
12.5
17.5 INPUT VOLTAGE
22.5
3501
3501
3501
FUNCTIONS
VIN1 (Pin VIN1 powers internal control circuitry both channels monitored undervoltage lockout comparator. VIN1 also connected collector channel on-chip power switch. VIN1 high dI/dt edges must decoupled ground close device. SW1/SW2 (Pins emitter onchip power NPN. switch off, inductor will drive this below ground with high dV/dt. external Schottky catch diode ground, close respective decoupling capacitor's ground, must used prevent this from excessive negative voltages. IND1/IND2 (Pins input on-chip sense resistor that measures current flowing inductor. When current resistor exceeds current dictated pin, latch held reset, disabling output switch. Bias current flows when less than 1.6V. VOUT1/VOUT2 (Pins VOUT output on-chip sense resistor that measures current flowing inductor. When current resistor exceeds current dictated pin, latch held reset, disabling output switch. Bias current flows VOUT when VOUT less than 1.6V. PG1/PG2 (Pins power good open-collector output that sinks current when feedback falls below nominal regulating voltage. VIN1 above output state remains true, although during shutdown, VIN1 undervoltage lockout thermal shutdown, current sink capability reduced. pins left open circuit tied together form single power good signal. VIN2 (Pin 10): VIN2 collector channel on-chip power switch. This independent VIN1 connected same separate supply. either case, high dI/dt edges present decoupling ground must used close this pin. SS1/SS2 (Pins 12): SS1/2 pins control softstart sequence their respective outputs. single capacitor from ground determines outpt ramp rate. soft-start output tracking/sequencing details, Applications Information section. VC1/VC2 (Pins 13): output error amplifier input peak switch current comparator. normally used frequency compensation, also used current clamp control loop override. error amplifier drives above maximum switch current level, voltage clamp activates.
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LT3501 FUNCTIONS
This indicates that output overloaded current pulled from pin, reducing regulation point. FB1/FB2 (Pins 14): negative input error amplifier. output switches regulate this 0.8V, with respect exposed ground pad. Bias current flows pin. SHDN (Pin 15): shutdown used turn both channels control circuitry reduce quiescent current typical value 9µA. accurate 1.28V threshold input current hysteresis used undervoltage lockout, preventing regulator from operating until input voltage reached predetermined level. Force SHDN above threshold float normal operation. RT/SYNC (Pin 16): This RT/SYNC provides modes setting constant switch frequency. Connecting resistor from RT/SYNC ground will RT/SYNC typical value 0.975V. resultant switching frequency will resistor value. minimum value 15.4k maximum value 133k sets switching frequency 1.5MHz 250kHz respectively. Driving RT/SYNC with external clock signal will synchronize switch applied frequency. Synchronization occurs rising edge clock signal after clock signal detected, with switch phase with synchronization signal. Each rising clock edge initiates oscillator ramp reset. gain control loop servos oscillator charging current maintain constant oscillator amplitude. Hence, slope compensation channel phase relationship remain unchanged. clock signal removed, oscillator reverts resistor mode reapplies 0.975V bias RT/SYNC after synchronization detection circuitry times out. clock source impedance should such that current RT/SYNC resistor mode generates frequency roughly equivalent synchronization frequency. BST1/BST2 (Pins 11): provides higher than base drive power ensure switch drop. comparator imposes minimum time voltage drops low. Forcing time allows boost capacitor recharge. Exposed (Pin 21): GND. Exposed only ground connection device. Exposed should soldered large copper area reduce thermal resistance. common both channels also serves small-signal ground. ideal operation small-signal ground paths should connect single point, avoiding high current ground returns.
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LT3501 BLOCK DIAGRAM
RT/SYNC VIN1 INTERNAL REGULATOR REFERENCE SLOPE COMPENSATION SHDN DRIVER CIRCUITRY CLK1 OSCILLATOR CLK2 CHANNEL
DROPOUT ENHANCEMENT
1.28V
SHUTDOWN COMPARATOR UNDERVOLTAGE
0.8V
LOWEST VOLTAGE 3.25µA CLAMP
SOFT-START RESET COMPARATOR
80mV
CLAMP
0.72V
Figure Block Diagram (One Switching Regulators Shown)
LT3501 dual channel, constant frequency, current mode buck converter with internal switches. Each channel identical with common shutdown pin, internal regulator, oscillator, undervoltage detect, thermal shutdown power-on reset. SHDN taken below 1.28V threshold LT3501 will placed quiescent current mode. this mode LT3501 typically draws from VIN1 <1µA from VIN2. shutdown mode active with typical sink capability 50µA VIN1 voltage greater than
When SHDN opened driven above 1.28V, internal bias circuits turn generating internal regulated voltage, 0.8VFB, 0.975V RT/SYNC references, signal which sets soft-start latch. RT/SYNC reaches 0.975V regulation point, internal oscillator will start generating clock signals 180° phase each regulator frequency determined resistor from RT/SYNC ground. Alternatively, synchronization signal detected LT3501 RT/SYNC pin, clock signals 180° phase
VOUT
POWER GOOD COMPARATOR
PGOOD
3501
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LT3501 BLOCK DIAGRAM
will generated incoming frequency rising edge synchronization pulse with switch phase with synchronization signal. addition, internal slope compensation will automatically adjusted prevent subharmonic oscillation during synchronization. regulators constant frequency, current mode step-down converters. Current mode regulators controlled internal clock feedback loops that control duty cycle power switch. addition normal error amplifier, there current sense amplifier that monitors switch current cycle-by-cycle basis. This technique means that error amplifier commands current delivered output rather than voltage. voltage system will have phase shift resonant frequency inductor output capacitor, then abrupt 180°, shift will occur. current system will have phase shift much lower frequency, will have additional shift until well beyond resonant frequency. This makes much easier frequency compensate feedback loop also gives much quicker transient response. Block Diagram Figure shows only switching regulators whose operation will discussed below. additional regulator will operate similar manner with exception that clock will 180° phase with other regulator. When, during power signal sets soft-start latch, both pins will discharged ground ensure proper start-up operation. When voltage drops below 80mV, driven disabling switching soft-start latch reset. Once latch reset soft-start capacitor starts charge with typical value 3.25µA. voltage rises above 80mV pin, will driven high error amplifier. When voltage exceeds 0.7V, clock set-pulse sets driver flip-flop which turns internal power switch. This causes current from VIN, through switch, inductor internal sense resistor, increase. When voltage drop across internal sense resistor exceeds predetermined level voltage pin, flip-flop reset internal switch turned off. Once switch turned inductor will drive voltage until external Schottky diode starts conduct, decreasing current inductor. cycle repeated with start each clock cycle. However, internal sense resistor voltage exceeds predetermined level start clock cycle, flip-flop will resulting further decrease inductor current. Since output current controlled voltage, output regulation achieved error amplifier continually adjusting voltage. error amplifier transconductance amplifier that compares voltage lowest voltage present either internal 0.8V reference. Compensation loop easily achieved with simple capacitor series resistor/capacitor from ground. Since driven constant current source, single capacitor soft-start will generate controlled linear ramp output voltage. current demanded output exceeds maximum current dictated clamp, will discharged, lowering regulation point until output voltage supported maximum current. When overload removed, output will soft-start from overload regulation point. VIN1 undervoltage detection thermal shutdown will soft-start latch, resulting complete soft-start sequence. switch driver operates from either voltage. external diode capacitor used generate drive voltage higher than saturate output maintain high efficiency. capacitor voltage sufficient, switch allowed operate 100% duty cycle. boost capacitor discharges towards level insufficient drive output NPN, comparator forces minimum cycle time, allowing boost capacitor recharge. power good comparator with 30mV hysteresis trips regulated output voltage. output open-collector that when output regulation allowing resistor pull desired voltage.
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LT3501
APPLICATIONS INFORMATION
Choosing Output Voltage
FREQUENCY (kHz)
1600 1400 FREQUENCY 1200 1000 PHASE
PHASE (DEG)
output voltage programmed with resistor divider between output pin. Choose resistors according should less avoid bias current errors. Reference designators refer Block Diagram Figure Choosing Switching Frequency LT3501 switching frequecy resistor Figure RT/SYNC internally regulated 0.975V. Setting resistor sets current RT/SYNC which determines oscillator frequency illustrated Figure switching frequency typically high possible reduce overall solution size. LT3501 employs techniques enhance dropout high frequencies efficiency maximum input voltage decrease switching losses minimum switch times. maximum recommended frequency approximated equation: Frequency (Hz) VOUT tON(MIN)
RESISTANCE
3501
Figure Frequency Phase RT/SYNC Resistance
following example along with data Table illustrates tradeoffs switch frequency selection. Example. 25V, VOUT 3.3V, IOUT 2.5A, Temperature 85°C tON(MIN) 200ns (85°C from Typical Characteristics graph), 0.6V, 0.4V (85°C) Frequency 200e-9
/SYNC (Figure Input Voltage Range Once switching frequency been determined, input voltage range regulator determined. minimum input voltage determined either LT3501's minimum operating voltage ~2.8V,
where forward voltage drop catch diode Figure voltage drop internal switch, tON(MIN) minimum time switch, maximum load current.
Table Efficiency Size Comparisons Different RRT/SYNC Values. 3.3V Output
EFFICIENCY FREQUENCY RT/SYNC VVIN1/2 VIN(MAX) 1.2MHz 20.5k 79.0% 1.5µH 22µH 63mm2 1.0MHz 26.7k 80.9% 2.2µH 47µH 66mm2 750kHz 38.3k 81.2% 3.3µH 47µF 66mm2 500kHz 61.9k 82.0% 4.7µH 47µF 66mm2 250kHz 133k 83.9% 10µH 100µF 172mm2 IN(MAX) defined highest input voltage that maintains constant output voltage ripple. *Inductor capacitor values chosen stability constant ripple current.
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LT3501 APPLICATIONS INFORMATION
maximum duty cycle. duty cycle fraction time that internal switch during clock cycle. Unlike
START-UP RUNNING 1000 CURRENT (mA) 10000
3501
VOUT 3.3V
most fixed frequency regulators, LT3501 will switch each clock cycle there sufficient voltage across boost capacitor Figure fully saturate output switch. Forced switch minimum time will only occur clock cycle when boost capacitor needs recharged. This operation same effect lowering clock frequency fixed time, resulting higher duty cycle lower minimum input voltage. resultant duty cycle depends charging times boost capacitor approximated following equation: DCMAX
Figure Minimum Input Voltage Load Current
Example: VOUT 3.3V, IOUT Frequency 1MHz, Temperature 25°C 0.1V, (from from boost characteristics specification), 0.4V, tON(MIN) 200ns DCMAX
where divided typical boost current from Electrical Characteristics table. This leads minimum input voltage VIN(MIN) DCMAX where voltage drop internal switch. Figure shows typical graph minimum input voltage load current 3.3V 1.8V application first page this data sheet. maximum input voltage determined absolute maximum ratings pins frequency minimum duty cycle. minimum duty cycle defined DCMIN tON(MIN) Frequency Maximum input voltage VIN(MAX VOUT DCMIN
VOLTAGE
VIN(MIN)
3.48 0.98
DCMIN tMIN(ON) 0.200 VIN(MAX 18.2V 0.200
Inductor Selection Maximum Output Current good first choice inductor value
VOUT VOUT
Note that LT3501 will regulate input voltage taken above calculated maximum voltage long maximum ratings pins violated. However operation this region input voltage will exhibit pulse skipping behavior.
where frequency With this value maximum load current will ~3A, independent input voltage. inductor's current rating must greater than your maximum load current
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LT3501 APPLICATIONS INFORMATION
saturation current should about higher. keep efficiency high, series resistance (DCR) should less than 0.05. applications with duty cycle about 50%, inductor value should chosen obtain inductor ripple current less than peak switch current. course, such simple design guide will always result optimum inductor your application. larger value provides slightly higher maximum load current, will reduce output voltage ripple. your load lower than 2.5A, then decrease value inductor operate with higher ripple current. This allows physically smaller inductor, with lower resulting higher efficiency. current inductor triangle wave with average value equal load current. peak switch current equal output current plus half peak-topeak inductor ripple current. LT3501 limits switch current order protect itself system from overload faults. Therefore, maximum output current that LT3501 will deliver depends current limit, inductor value, switch frequency, input output voltages. inductor chosen based output current requirements, output voltage ripple requirements, size restrictions efficiency goals. When switch off, inductor sees output voltage plus catch diode drop. This gives peak-to-peak ripple current inductor:
FREQUENCY (kHz)
3.5A over entire duty cycle range. maximum output current function chosen inductor value: IOUT(MAX ILIM
inductor value chosen that ripple current small, then available output current will near switch current limit. approach choosing inductor start with simple rule given above, look available inductors choose meet cost space goals. Then these equations check that LT3501 will able deliver required output current. Note again that these equations assume that inductor current continuous. Discontinuous operation occurs when IOUT less than IL/2 calculated above. Figure illustrates inductance value needed 3.3V output with maximum load capability Referring Figure inductor value between 3.3µH 4.7µH will sufficient input voltage switch frequency 750kHz. There several graphs Typical Performance Characteristics section this data sheet that show inductor selection function input voltage switch frequency several popular output voltages output ripple currents. Also, inductance
1500 VOUT 3.3V IRIPPLE 2.2µH 1000
1250
DC)( VOUT
3.3µH
where switching frequency LT3501 value inductor. peak inductor switch current ISW(PK ILPK IOUT
4.7µH 6.8µH
INPUT VOLTAGE
3501
maintain output regulation, this peak current must less than LT3501's switch current limit ILIM. ILIM
Figure Inductor Values Maximum Load Current Frequency Input Voltage
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LT3501 APPLICATIONS INFORMATION
result discontinuous mode operation, which okay, further reduces maximum load current. details maximum output current discontinuous mode operation, Linear Technology Application Note Finally, duty cycles greater than (VOUT/VIN 0.5), there minimum inductance required avoid subharmonic oscillations. Application Note more information. Input Capacitor Selection Bypass inputs LT3501 circuit with 4.7µF higher ceramic capacitor type. lower value less expensive type used there additional bypassing provided bulk electrolytic tantalum capacitors. following paragraphs describe input capacitor considerations more detail. Step-down regulators draw current from input supply pulses with very fast rise fall times. input capacitor required reduce resulting voltage ripple LT3501 force this very high frequency switching current into tight local loop, minimizing EMI. input capacitor must have impedance switching frequency this effectively, must have adequate ripple current rating. With switchers operating same frequency with different phases duty cycles, calculating input capacitor current simple. However, conservative value input current channel that delivering most power (VOUT IOUT). This given CIN(RMS) IOUT VOUT VOUT IOUT ments input capacitor. Determine worst-case condition input ripple current then size input capacitor such that reduces input voltage ripple acceptable level. Typical values input capacitors from 10µF frequencies 2.2µF higher frequencies. combination small size impedance (low equivalent series resistance ESR) ceramic capacitors make them preferred choice. results very voltage ripple capacitors handle plenty ripple current. They also comparatively robust used this application their rated voltage. types stable over temperature applied voltage, give dependable service. Other types (Y5V Z5U) have very large temperature voltage coefficients capacitance, they have only small fraction their nominal capacitance your application. While they will still handle ripple current, input voltage ripple become fairly large, ripple current flowing from your input supply from other bypass capacitors your system, opposed being fully sourced from local input capacitor. alternative high value ceramic capacitor lower value along with larger electrolytic capacitor, example ceramic capacitor parallel with tantalum capacitor. electrolytic capacitor, value larger than 10µF will required meet ripple current requirements. Because input capacitor likely high surge currents when input source applied, tantalum capacitors should surge rated. manufacturer also recommend operation below rated voltage capacitor. sure place ceramic close possible pins optimal noise immunity. When LT3501's input supplies operated different input voltages, input capacitor sized that channel should placed close possible respective pins. final caution regarding ceramic capacitors input. ceramic input capacitor combine with stray inductance form resonant tank circuit. power applied quickly (for example plugging circuit into live power source) this tank ring, doubling input voltage damaging LT3501. solution
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largest when 2VOUT (50% duty cycle). second, lower power channel draws input current, input capacitor's current actually decreases out-of-phase current cancels current drawn higher power channel. Considering that maximum load current from single channel ~3A, ripple current will always less than 1.5A. frequency, VOUT ratio, maximum load current requirement LT3501 along with input supply source impedance, determine energy storage require-
LT3501 APPLICATIONS INFORMATION
either clamp input voltage dampen tank circuit adding lossy capacitor parallel with ceramic capacitor. details, Application Note Output Capacitor Selection Typically step-down regulators easily compensated with output crossover frequency that 1/10 switching frequency. This means that time that output capacitor must supply output load during transient step switching periods. With allowable drop output voltage during step, good starting value output capacitor expressed CVOUT Example: VOUT 3.3V, Frequency 1MHz, Load Step CVOUT 12µF 0.05 3.3V Load Step Frequency 0.05 VOUT content this ripple very low, current rating output capacitor usually concern. Another constraint output capacitor that must have greater energy storage than inductor; stored energy inductor transferred output, would like resulting voltage step small compared regulation voltage. overshoot, this requirement becomes COUT VOUT
Finally, there must enough capacitance good transient performance. last equation gives good starting point. Alternatively, start with designs this data sheet experiment desired performance. This topic covered more thoroughly section loop compensation. high performance (low ESR), small size robustness ceramic capacitors make them preferred type LT3501 applications. However, ceramic capacitors same. mentioned above, many high value capacitors poor dielectrics with high temperature voltage coefficients. particular, types lose large fraction their capacitance with applied voltage temperature extremes. Because loop stability transient response depend value COUT, able tolerate this loss. types. also electrolytic capacitors. ESRs most aluminum electrolytics large deliver output ripple. Tantalum newer, lower organic electrolytic capacitors intended power supply use, suitable manufacturers will specify ESR. choice capacitor value will based required ripple. Because volume capacitor determines ESR, both size value will larger than ceramic capacitor that would give similar ripple performance. benefit that larger capacitance give better transient response large changes load current. Table lists several capacitor vendors.
calculated value only suggested starting value. Increase value transient response needs improvement reduce capacitance size priority. output capacitor filters inductor current generate output with voltage ripple. also stores energy order satisfy transient loads stabilize LT3501's control loop. switching frequency LT3501 determines value output capacitance required. Also, current mode control loop doesn't require presence output capacitor series resistance (ESR). these reasons, free ceramic capacitors achieve very output ripple small circuit size. Estimate output ripple with following equations: VRIPPLE IL/(8f COUT) ceramic capacitors, VRIPPLE electrolytic capacitors (tantalum aluminum) where peak-to-peak ripple current inductor.
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LT3501 APPLICATIONS INFORMATION
Table
VENDOR Taiyo Yuden Kemet TYPE Ceramic X5R, Ceramic X5R, Tantalum Tantalum Organic Organic TA/AL Organic Organic Ceramic X5R, T491, T494, T495 T520 A700 POSCAP SERIES
where IOUT(MAX) maximum load current, VBST(MIN) minimum boost voltage fully saturate switch. Figure shows four ways arrange boost circuit. must more than 1.4V above full efficiency. Generally, outputs 3.3V higher standard circuit (Figure best. outputs between 2.8V 3.3V, replace with small Schottky diode such PMEG4005. lower output voltages boost diode tied input (Figure 5b). circuit Figure more efficient because current comes from lower voltage source. Figure shows boost voltage source from available sources that greater than highest efficiency attained choosing lowest boost voltage above example, generating 3.3V 1.8V 3.3V whenever 1.8V 1.8V boost diode connected 3.3V output. case, must also sure that maximum voltage less than maximum specified Absolute Maximum Ratings section. boost circuit also directly from voltage that higher than input voltage more than Figure diode used prevent damage LT3501 case held while present. circuit saves several components (both pins tied D2). However, efficiency lower dissipation LT3501 higher. Also, absent, LT3501 will still attempt regulate output, will with very efficiency high dissipation because switch will able saturate, dropping 1.5V conduction. minimum input voltage LT3501 application limited minimum operating voltage (<3V) maximum duty cycle outlined above. proper start-up, minimum input voltage also limited boost circuit. input voltage ramped slowly, LT3501 turned with when output already regulation, then boost capacitor fully charged. Because boost capacitor charged with energy stored inductor, circuit will rely some minimum load current boost circuit running properly. This minimum load will depend
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Sanyo Panasonic
Catch Diode diode conducts current only during switch time. Schottky diode limit forward voltage drop increase efficiency. Schottky diode must have peak reverse voltage that equal regulator input voltage sized average forward current normal operation. Average forward current calculated from: AVG) IOUT VOUT
only reason consider larger diode worstcase condition high input voltage shorted output. With shorted condition, diode current will increase typical value determined peak switch current limit LT3501. This safe short periods time, would prudent check with diode manufacturer continuous operation under these conditions tolerated. Considerations capacitor diode tied generate voltage that higher than input voltage. most cases 0.47µF capacitor fast switching diode (such CMDSH-3 FMMD914) will work well. Almost type film ceramic capacitor suitable, should ensure fully recharged during time switch. capacitor value approximated CBST
VOUT VBST(MIN)
IOUT(MAX
LT3501 APPLICATIONS INFORMATION
LT3501 VOUT VBST VOUT VBST(MAX) VOUT LT3501 VOUT VBST VBST(MAX)
VOUT
VOUT
(5a)
LOWEST VOUT LT3501 VOUT VBST VBST(MAX) VX(MIN)
(5b)
LT3501 VOUT VBST VBST(MAX) VX(MIN)
3501
VOUT
VOUT
(5c)
(5d)
Figure Considerations
input output voltages, arrangement boost circuit. Typical Performance Characteristics section shows plots minimum load current start function input voltage 3.3V outputs. many cases discharged output capacitor will present load switcher which will allow start. plots show worst-case situation where ramping very slowly. Schottky diode lowest start-up voltage. Frequency Compensation LT3501 uses current mode control regulate output. This simplifies loop compensation. particular, LT3501 does require output capacitor stability free ceramic capacitors achieve output ripple small circuit size. Frequency compensation provided components tied pin. Generally capacitor resistor series ground determine loop gain. addition, there lower value capacitor parallel. This capacitor
part loop compensation used filter noise switching frequency. Loop compensation determines stability transient performance. Designing compensation network complicated best values depend application particular type output capacitor. practical approach start with circuits this data sheet that similar your application tune compensation network optimize performance. Stability should then checked across operating conditions, including load current, input voltage temperature. LT1375 data sheet contains more thorough discussion loop compensation describes test stability using transient load. Figure shows equivalent circuit LT3501 control loop. error transconductance amplifier with finite output impedance. power section, consisting modulator, power switch inductor, modeled transconductance amplifier generating output current proportional voltage pin. Note that
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LT3501 APPLICATIONS INFORMATION
LT3501 CURRENT MODE POWER STAGE 3mho 275µmho 3.6M CERAMIC OUTPUT
ERROR
Figure Model Loop Response
output capacitor integrates this current, that capacitor (CC) integrates error amplifier output current, resulting poles loop. most cases zero required comes from either output capacitor from resistor series with This simple model works well long value inductor high loop crossover frequency much lower than switching frequency. phase lead capacitor (CPL) across feedback divider improve transient response. Synchronization RT/SYNC used synchronize regulators external clock source. Driving RT/SYNC resistor with clock source triggers synchronization detection circuitry. Once synchronization detected, rising edge will synchronized rising edge RT/SYNC signal. loop will adjust internal oscillators maintain degree phase between SW2, also adjust slope compensation avoid subharmonic oscillation. synchronizing clock signal input LT3501 must have frequency between 250kHz 1.5MHz, duty cycle between 80%, state below 0.5V high state above 1.6V. Synchronization signals outside these parameters will cause erratic switching behavior. RT/SYNC resistor should such that free running frequency ((VRT/SYNC VSYNCLO)/RRT/SYNC) approximately equal synchronization frequency. synchronization signal halted, synchronization detection circuitry will timeout typically 10µs which
0.8V
TANTALUM POLYMER
3501
VOUT1 LT3501 RT/SYNC
SYNCHRONIZATION CIRCUITRY
3501
Figure Synchronous Signal Powered from Regulator's Output
time LT3501 reverts free-running frequency based current through RT/SYNC. RT/SYNC resistor held above 1.6V time, switching will disabled. synchronization signal present during regulator start-up (for example, synchronization circuitry powered from regulator output) RT/SYNC must equivalent resistance ground between 15.4k 133k until synchronization circuitry active proper start-up operation. synchronization signal powers undetermined state (VOL, VOH, Hi-Z), connect synchronization clock LT3501 shown Figure circuit shown will isolate synchronization signal when output voltage below regulated output. LT3501 will start-up with switching frequency determined resistor from RT/SYNC ground. synchronization signal powers impedance state (VOL), connect resistor between RT/SYNC synchronizing clock. equivalent resistance seen from RT/SYNC ground will start-up frequency.
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LT3501 APPLICATIONS INFORMATION
synchronization signal powers high impedance state (Hi-Z), connect resistor from RT/SYNC ground. equivalent resistance seen from RT/SYNC ground will start-up frequency. synchronization signal changes between high impedance states during power (VOL, Hi-Z), connect synchronization circuitry LT3501 shown Typical Applications section. This will allow LT3501 start-up with switching frequency determined equivalent resistance from RT/SYNC ground. Shutdown Undervoltage Lockout Figure shows undervoltage lockout (UVLO) LT3501. Typically, UVLO used situations where input supply current limited, relatively high source resistance. switching regulator draws constant power from source, source current increases source voltage drops. This looks like negative resistance load source cause source current limit latch under source voltage conditions. UVLO prevents regulator from operating source voltages where these problems might occur. internal comparator will force part into shutdown below minimum VIN1 2.8V. This feature used prevent excessive discharge battery-operated systems. Since VIN2 supplies output stage channel monitored, care must taken insure that VIN2 present before channel allowed switch. adjustable UVLO threshold required, SHDN used. threshold voltage SHDN comparator 1.28V. internal current source
LT3501 VIN1
defaults open-pin condition operating (see Typical Performance Characteristics). Current hysteresis added above SHDN threshold. This used voltage hysteresis UVLO using following: 1.28 1.28
Turn-on threshold Turn-off threshold Example: switching should start until input above 4.75V stop input falls below 3.75V. 4.75V 3.75V 4.75 3.75 143k 1.28 4.75 1.28 143k
Keep connections from resistors SHDN short make sure that interplane surface capacitance switching nodes minimized. high resistor values used, SHDN should bypassed with capacitor prevent coupling problems from switch node. Soft-Start output LT3501 regulates lowest voltage present either internal 0.8V reference. capacitor from ground charged internal 3.25µA current source resulting linear output ramp from regulated output whose duration given tRAMP 3.25µA
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VIN1 2.8V VIN1 VIN2
SHDN
1.28V
Figure Undervoltage Lockout
INTERNAL REGULATOR
3501
LT3501 APPLICATIONS INFORMATION
power-up, reset signal sets soft-start latch discharges both pins approximately ensure proper start-up. When both pins fully discharged latch reset internal 3.25µA current source starts charge pin. When voltage below 50mV, pulled which disables switching. This allows used individual shutdown each channel. voltage rises above 50mV, released output regulated voltage. When voltage exceeds internal 0.8V reference, output regulated reference. voltage will continue rise until clamped event VIN1 undervoltage lockout, SHDN driven below 1.28V, internal temperature exceeding maximum rating during normal operation, soft-start latch set, triggering start-up sequence. addition, load exceeds maximum output switch current, output will start drop causing clamp activated. long clamped, will discharged. result, output will regulated highest voltage that maximum output current support. example, output loaded will drop 0.53V, regulating output Once overload condition removed, output will soft-start from temporary voltage level normal regulation point. Since clamped discharge 0.8V before taking control regulation, momentary overload conditions will tolerated without soft-start recovery. typical time before takes control tSS(CONTROL) 1.2V 700µA threshold exceeded. active (sink capability reduced shutdown undervoltage lockout mode) long VIN1 voltage exceeds Output Tracking/Sequencing Complex output tracking sequencing between channels implemented using LT3501's pins. Figure shows several configurations output tracking/sequencing 3.3V 1.8V application. Independent soft-start each channel shown Figure output ramp time each channel soft-start capacitor described soft-start section. Ratiometric tracking achieved Figure connecting both pins together. this configuration, source current doubled (6.5µA) which must taken into account when calculating output rise time. connecting feedback network from VOUT1 with same ratio that sets VOUT2 voltage, absolute tracking shown Figure implemented. minimum value feedback resistor (R1) should such that driven ground with 700µA sink current when VOUT1 regulated voltage. addition, small VOUT2 voltage offset will present 3.25µA source current. This offset corrected slightly reducing value Figure illustrates output sequencing. When VOUT1 within regulated voltage, releases soft-start allowing VOUT2 soft-start. this case will pulled pin. greater voltage needed logic, pull-up resistor VOUT1 used. This will decrease soft-start ramp time increase tolerance momentary shorts. precise output ramp down required, drive pins shown Figure minimum value resistor (R3) should such that driven ground with 700µA sink current during power-up fault conditions. Multiple Input Voltages applications requiring large inductors high VOUT ratios, 2-stage step-down approach reduce
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Power Good Indicators open-collector output internal comparator. comparator compares voltage reference voltage with 30mV hysterisis. sink capability 800µA when below threshold withstand when
LT3501 APPLICATIONS INFORMATION
Independent Start-Up
VOUT1 0.5V/DIV VOUT2 0.5V/DIV VOUT2 0.5V/DIV
Ratiometric Start-Up
VOUT1 0.5V/DIV
Absolute Start-Up
VOUT1 0.5V/DIV VOUT2 0.5V/DIV
5ms/DIV
10ms/DIV
10ms/DIV
0.1µF
VOUT1 LT3501
3.3V 0.1µF
VOUT1 LT3501
3.3V 0.22µF
VOUT1 LT3501
3.3V
0.22µF
VOUT2
1.8V
VOUT2
1.8V
VOUT2 13.7k
1.8V
8.08k
(9a) Output Sequencing
VOUT1 0.5V/DIV
(9b) Controlled Power Down
(9c)
VOUT1 0.5V/DIV
VOUT2 0.5V/DIV
VOUT2 0.5V/DIV
SS1/2
10ms/DIV 0.1µF VOUT1 LT3501 0.1µF VOUT2 1.8V 3.3V EXTERNAL SOURCE
10ms/DIV
VOUT1 LT3501
3.3V
VOUT2
1.8V
(9d)
(9e)
Figure
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LT3501 APPLICATIONS INFORMATION
4.7µF PMEG4005
VIN1 SHDN 3.3µH PMEG4005 BST1 0.47µF B360A IND1 VOUT1 47µF 42.3k 8.06k 470pF LT3501
VIN2 FSET BST2
26.7k
0.47µF B360A IND2 VOUT2 100k
VOUT1
47µF
VOUT2 1.2V
SS/TRACK1 SS/TRACK2
8.06k 470pF
10pF
40.2k
0.1µF
0.1µF
32.4k
10pF
3501
Figure 1.2V 2-Stage Step-Down Converter with Output Sequencing
inductor size allowing increase frequency. dual step down application (Figure steps down input voltage (VIN1) highest output voltage then uses that voltage power second output (VIN2). VOUT1 must able provide enough current output plus VOUT2 maximum load. Note that VOUT1 must above VIN2 minimum input voltage (2V) when second channel starts switch. Delaying channel accomplished either independent soft-start capacitors sequencing with output. example, assume maximum input 24V: 24V, VOUT1 1.5A VOUT2 1.2V 1.5A VOUT Frequency (Hz) tMIN(ON)
Single Step Down: Frequency (Hz) 392kHz 190ns
392kHz
10µH
1.2) 2.7µH
392kHz
2-Stage Step-Down: Frequency 1.2MHz 190ns Frequency 1.2MHz
VOUT VOUT
1.2MHz 1.2MHz
3.3µH
1.2) 0.76µH
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LT3501 APPLICATIONS INFORMATION
LT3501 LT3501 LT3501
(11a)
(11b)
(11c)
Figure Subtracting Current when Switch (11a) from Current when Switch (11b) Reveals Path High Frequency Switching Current (11c). Keep this Loop Small. Voltage Traces will Also Switched; Keep These Traces Short Possible. Finally, Make Sure Circuit Shielded with Local Ground Plane
Layout proper operation minimum EMI, care must taken during printed circuit board (PCB) layout. Figure shows high di/dt paths buck regulator circuit. Note that large switched currents flow power switch, catch diode input capacitor. loop formed these components should small possible. These components, along with inductor output capacitor, should placed same side circuit board their connections should made that layer. Place local, unbroken ground plane below these components, this ground plane system ground
location, ideally ground terminal output capacitor Additionally, traces should kept short possible. topside metal from DC964A demonstration board Figure illustrates proper component placement trace routing. Thermal Considerations must also provide heat sinking keep LT3501 cool. exposed metal bottom package must soldered ground plane. This ground should tied other copper layers below with thermal vias; these layers will spread heat dissipated
Figure Topside Layout DC964A
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LT3501 APPLICATIONS INFORMATION
LT3501. Place additional vias near catch diodes. Adding more copper bottom layers tying this copper internal planes with vias further reduce thermal resistance. With these steps, thermal resistance from junction) ambient reduced 45°C/W. power dissipation other power components such catch diodes, boost diodes inductors, cause additional copper heating further increase what sees ambient temperature. LT1767 data sheet's Thermal Considerations section. Single, Ripple Output LT3501 generate single, ripple output outputs switching regulators tied together share single output capacitor. tying pins together pins together, channels will share load current. There several advantages this 2-phase buck regulator. Ripple currents input output reduced, reducing voltage ripple allowing smaller, less expensive capacitors. Although inductors required, each will smaller than inductor required single-phase regulator. This important when there tight height restrictions circuit. There special consideration regarding 2-phase circuit. When difference between input voltage output voltage less than 2.5V, then boost circuits prevent channels from properly sharing current. example, channel gets started first, supply load current, while channel never switches enough current boost capacitor charged. this case, channel will supply load until reaches current limit, output voltage drops, channel gets started. solutions this problem shown Typical Applications section. single 3.3V/6A output converter generates boost supply from either that will service both switch pins. synchronized 3.3V/12A output converter utilizes undervoltage lockout prevent start-up condition. Other Linear Technology Publications Application notes AN19, AN35 AN44 contain more detailed descriptions design information buck regulators other switching regulators. LT1376 data sheet more extensive discussion output ripple, loop compensation stability testing. Design Note DN100 shows generate dual output supply using buck regulator.
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LT3501 TYPICAL APPLICATIONS
2.5V with Absolute Tracking
4.7µF VIN1 SHDN 3.3µH PMEG4005 BST1 0.47µF B360A IND1 VOUT1 47µF 42.3k 100k SS/TRACK1 SS/TRACK2 0.1µF
3501 TA02
VIN2 RT/SYNC BST2
26.7k
0.47µF LT3501 IND2 VOUT2 100k
2.2µH B360A PMEG4005
VOUT1
16.9k
47µF
VOUT2 2.5V
470pF 8.06k 16.9k 10pF 40.2k
470pF 40.2k 10pF 8.06k
7.68k
1.25MHz Single 3.3V/6A Ripple Output
4.7µF VIN1 SHDN BST1 0.47µF PMEG4005 VOUT1 3.3V B360A IND1 VOUT1 47µF 24.9k 100k 8.06k 1000pF 22pF 17.8k 0.1µF LT3501 IND2 VOUT2 B360A PMEG4005 VIN2 RT/SYNC BST2
20.5k
1.5µH
0.47µF 1.5µH
SS/TRACK1 SS/TRACK2
3501 TA03
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LT3501 TYPICAL APPLICATIONS
1.25MHz Single 3.3V/6A Ripple Output
4.5V 4.7µF 1µF* VIN1 SHDN PMEG4005* 1.5µH PMEG4005 VOUT1 3.3V BST1 0.47µF B360A IND1 VOUT1 47µF 24.9k 100k 8.06k 1000pF 22pF 17.8k 0.1µF LT3501 IND2 VOUT2 B360A PMEG4005 VIN2 RT/SYNC BST2 20.5k PMEG4005* 0.47µF 1.5µH
SS/TRACK1 SS/TRACK2
3501 TA03
*ADDITIONAL COMPONENTS ADDED SHOW BOOST VOLTAGE WHEN <6V. THIS REQUIRED ENSURE LOAD SHARING BETWEEN CHANNELS.
Dual LT3501 Synchronized 3.3V/12A Output, 3MHz Effective Switch Frequency
5.5V 10µF 143k 36.5k VIN1 SHDN BST1 0.47µF PMEG4005 B360A IND1 VOUT1 24.9k LT3501 IND2 VOUT2 B360A PMEG4005 VIN2 RT/SYNC BST2 0.47µF 3.3µH
3.3µH
VOUT1 3.3V
47µF 8.06k
49.9k 49.9k OUT1 133k LTC6908-1 OUT2 49.9k
3300pF 47pF 15.3k
SS/TRACK1 SS/TRACK2 0.1µF
PMEG4005
VIN1 SHDN BST1 0.47µF B360A IND1 VOUT1
VIN2 RT/SYNC BST2 0.47µF
PMEG4005
3.3µH
3.3µH B360A
LT3501 IND2 VOUT2
49.9k
SS/TRACK1 SS/TRACK2
3501 TA04
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LT3501 PACKAGE DESCRIPTION
Package 20-Lead Plastic TSSOP (4.4mm)
(Reference 05-08-1663)
Exposed Variation
4.95 (.195) 6.40 6.60* (.252 .260) 4.95 (.195) 1918
6.60 ±0.10 4.50 ±0.10
NOTE
2.74 (.108) 0.45 ±0.05 1.05 ±0.10 0.65
6.40 2.74 (.252) (.108)
RECOMMENDED SOLDER LAYOUT
1.20 (.047)
4.30 4.50* (.169 .177)
0.25
0.09 0.20 (.0035 .0079)
0.50 0.75 (.020 .030)
0.65 (.0256)
NOTE: CONTROLLING DIMENSION: MILLIMETERS MILLIMETERS DIMENSIONS (INCHES) DRAWING SCALE
0.195 0.30 (.0077 .0118)
0.05 0.15 (.002 .006)
FE20 (CA) TSSOP 0204
RECOMMENDED MINIMUM METAL SIZE EXPOSED ATTACHMENT *DIMENSIONS INCLUDE MOLD FLASH. MOLD FLASH SHALL EXCEED 0.150mm (.006") SIDE
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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.
LT3501 RELATED PARTS
PART NUMBER LT1766 LT1933 LT1936 LT1940 LT1976/LT1977 DESCRIPTION 60V, 1.2A (IOUT), 200kHz High Efficiency Step-Down DC/DC Converter 500mA (IOUT), 500kHz Step-Down Switching Regulator SOT-23 36V, 1.4A (IOUT), 500kHz High Efficiency Step-Down DC/DC Converter Dual 25V, 1.4A (IOUT), 1.1MHz High Efficiency Step-Down DC/DC Converter 60V, 1.2A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode® Operation COMMENTS VIN: 5.5V 60V, VOUT(MIN) 1.20V, 2.5mA, 25µA, 16-Lead TSSOPE Package VIN: 3.6V 36V, VOUT(MIN) 1.2V, 1.6mA, <1µA, ThinSOTPackage VIN: 3.6V 36V, VOUT(MIN) 1.2V, 1.9mA, <1µA, 8-Lead MS8E Package VIN: 3.6V 25V, VOUT(MIN) 1.20V, 3.8mA, <30µA, 16-Lead TSSOPE Package VIN: 3.3V 60V, VOUT(MIN) 1.20V, 100µA, <1µA, 16-Lead TSSOPE Package VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 40µA, <1µA, 10-Lead Packages VIN: 3.3V 60V, VOUT(MIN) 1.20V, 100µA, <1µA, 16-Lead TSSOPE Package
LTC®3407/LTC3407-2 Dual 600mA/800mA, 1.5MHz/2.25MHz Synchronous Step-Down DC/DC Converters LT3434/LT3435 LT3437 LT3493 LT3505 LT3506/LT3506A LT3510 LTC3548 60V, 2.4A (IOUT), 200kHz/500kHz High Efficiency Step-Down DC/DC Converters with Burst Mode Operation
60V, 400mA (IOUT), Micropower Step-Down DC/DC Converter VIN: 3.3V 60V, VOUT(MIN) 1.25V, 100µA, <1µA, with Burst Mode Operation Package 36V, 1.4A (IOUT), 750kHz High Efficiency Step-Down DC/DC Converter 36V, 1.2A (IOUT), 3MHz High Efficiency Step-Down DC/DC Converter Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz High Efficiency Step-Down DC/DC Converters Dual 25V, (IOUT), 1.5MHz High Efficiency Step-Down DC/DC Converter Dual 400mA/800mA, 2.25MHz Synchronous Step-Down DC/DC Converters VIN: 3.6V 36V, VOUT(MIN) 0.8V, 1.9mA, <1µA, Package VIN: 3.6V 36V, VOUT(MIN) 0.78V, 2mA, <2µA, 8-Lead Packages VIN: 3.6V 25V, VOUT(MIN) 0.8V, 3.8mA, <30µA, Package VIN: 3.3V 25V, VOUT(MIN) 0.8V, 3.5mA, <1µA, 20-Lead TSSOPE Package VIN: 2.5V 5.5V, VOUT(MIN) 0.6V, 40µA, <1µA, 10-Lead Packages
Burst Mode registered trademark Linear Technology Corporation. ThinSOT trademark Linear Technology Corporation.
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Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
0507 PRINTED
1630 McCarthy Blvd., Milpitas, 95035-7417
www.linear.com
LINEAR TECHNOLOGY CORPORATION 2006
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