LM26480 Externally Programmable Dual High-Current Step-Down DC/DC Dual

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LM26480 Externally Programmable Dual High-Current Step-Down DC/DC Dual

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LM26480Externally Programmable Dual High-Current Step-Down DC/DC Dual Linear Regulators
LM26480 Externally Programmable Dual High-Current Step-Down DC/DC Dual Linear Regulators
LM26480 multi-functional Power Management Unit, optimized low-power digital applications. This device integrates highly efficient 1.5A step-down DC/DC converters linear regulators. LM26480 offered tiny 0.8mm LLP-24 package. Linear Regulators (LDO) VOUT 1.0V-3.5V voltage accuracy output current (typ) dropout
Specifications
Step-Down DC/DC Converter (Buck) 1.5A output current VOUT from: Buck1 0.8V-2.0V 1.5A Buck2 1.0V-3.3V 1.5A efficiency voltage accuracy switching frequency automatic mode change under loads Automatic soft start
Features
Compatible with advanced applications processors
FPGAs LDOs powering Internal processor functions I/Os Precision internal reference Thermal overload protection Current overload protection 24-lead 0.8mm package External Power-On-Reset function Buck1 Buck2 Undervoltage lock-out detector monitor input supply voltage
Applications
Core digital power Applications processors Peripheral power
Typical Application Circuit
30040401
2008 National Semiconductor Corporation
300404
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LM26480
30040402
FIGURE Application Circuit
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LM26480
Connection Diagrams Package Mark Information
30040403
FIGURE 24-Lead Package (top view)
Note: physical placement package marking will vary from part part. UZXYTT format: wafer code; assembly code; 'XY' digit date code; `TT" code. marking_conventions.html more information marking information.
Part Number LM26480SQ-AA LM26480SQX-AA
Spec NOPB NOPB
Quantity 1000 tape reel 4500 tape reel
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LM26480
Descriptions
Name VINLDO12 SYNC Type G/(D) Description Analog Power Internal Functions (VREF, BIAS, I2C, Logic) Frequency Synchronization which allows user connect external clock signal synchronize PMIC internal oscillator. Default must grounded when used. Contact National Sales office enable. nPOR Power reset both Buck1 Buck Open drain logic output 100K pullup resistor. nPOR pulled ground when voltages these supplies good. nPOR section more info. Buck1 NMOS Power Ground Buck1 switcher output Power from either source Battery Buck1 Enable Buck1 switcher, logic HIGH enables Buck1. cannot left floating. Buck1 input feedback terminal Non-switching core ground Analog Power Buck converters Buck2 input feedback terminal Enable Buck2 switcher, logic HIGH enables Buck2. cannot left floating. Power from either source Battery Buck2 Buck2 switcher output Buck2 NMOS LDO2 enable pin, logic HIGH enables LDO2. cannot left floating. LDO1 enable pin, logic HIGH enables LDO1. cannot left floating. ground Power from either source battery LDO1 LDO1 Output LDO1 Feedback Terminal LDO2 Feedback Terminal Output Power from either source battery LDO2.
Input I/O: Input/Output Output
NPOR
Analog
GND_SW1 VIN1 ENSW1 GND_C AVDD ENSW2 VIN2 GND_SW2 ENLDO2 ENLDO1 GND_L VINLDO1 LDO1 FBL1 FBL2 LDO2 VINLDO2
Digital
Ground
PWR: Power
Power Block Operation Power Block Input VINLDO12 AVDD VIN1 VIN2 VINLDO1 VINLDO2 Enabled VIN+ VIN+ VIN+ VIN+ Disabled VIN+ VIN+ VIN+ VIN+
Note Always Powered Always Powered
VIN+ VIN+
VIN+ VIN+
Enabled, 1.74V Enabled, 1.74V
VIN+ largest potential voltage device.
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LM26480
Absolute Maximum Ratings (Notes
Military/Aerospace specified devices required, please contact National Semiconductor Sales Office/ Distributors availability specifications. VINLDO12, VIN1, AVDD, VIN2, VINLDO1, VINLDO2, ENSW1, FB1, FB2, ENSW2, ENLDO1, ENLDO2, SYNC, FBL1, FBL2 -0.3V SLUG ±0.3V Power Dissipation (PD_MAX) (TA=85°C, TMAX=125°C (Note 1.17W Junction Temperature (TJ-MAX) 150°C Storage Temperature Range -65°C +150°C Maximum Lead Temperature (Soldering) 260°C Ratings Human Body Model (Note
Operating Ratings: Bucks
Junction Temperature (TJ) Range Ambient Temperature (TA) Range (Note
(Notes
2.8V 5.5V (VIN 0.3V) -40°C +125°C -40°C +85°C
Thermal Properties
Junction-to-Ambient Thermal Resistance (JA) SQA024AG
(Notes 34.1°C/W
(Notes Unless otherwise noted, 3.6V. Typical values limits appearing normal type apply 25°C. Limits appearing boldface type apply over entire junction temperature range operation, -40°C +125°C. Symbol VPOR TSDH UVLO Parameter VINLDO12 Shutdown Current Power-On Reset Threshold Thermal Shutdown Threshold Themal Shutdown Hysteresis Under Voltage Lock Conditions 3.6V Falling Edge(Note (Note (Note Rising Failing Units
General Electrical Characteristics
Drop Regulators, LDO1 LDO2
Unless otherwise noted, 3.6V, COUT 0.47 Typical values limits appearing normal type apply 25°C. Limits appearing boldface type apply over entire junction temperature range operation, -40°C +125°C. (Notes Symbol VOUT Parameter Operational Voltage Range Voltage Accuracy Line Regulation Load Regulation VOUT PSRR Short Circuit Current Limit Dropout Voltage Power Supply Ripple Rejection Supply Output Noise Quiescent Current "On" Quiescent Current "On" Quiescent Current "Off" Turn Time (VOUT 0.3V) 5.0V (Note Load Current 3.6V, Load Current IMAX LDO1-2, VOUT Load Current (Note kHz, Load Current IMAX IOUT IOUT de-asserted Start from shut-down 0.03 Conditions VINLDO1 VINLDO2 PMOS pins (Note 1.74 0.15 0.011 Units %/mA µVrms µsec
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LM26480
Symbol COUT
Parameter Output Capacitor
Conditions Capacitance stability 125°C -40°C 125°C (Equivalent Series Resistance)
0.33 0.68
0.47
Units
Buck Converters SW1,
Unless otherwise noted, 3.6V, COUT LOUT Typical values limits appearing normal type apply 25°C. Limits appearing boldface type apply over entire junction temperature range operation, -40°C +125°C. ((Notes Symbol VOUT Parameter Line Regulation Load Regulation ISHDN fOSC IPEAK RDSON RDSON Efficiency Shutdown Supply Current Internal Oscillator Frequency Buck1 Peak Switching Current Limit Buck2 Peak Switching Current Limit Quiescent Current "On" Pin-Pin Resistance PFET Pin-Pin Resistance NFET Turn Time Input Capacitor Output Capacitor Start from shut-down Capacitance stability Capacitance stability load Mode Conditions IMAX Load Current de-asserted 0.089 0.0013 0.01 Units %/mA µsec (Note Feedback Voltage
Electrical Characteristics
Unless otherwise noted: Typical values limits appearing normal type apply 25°C. Limits appearing boldface type apply over entire junction temperature range operation, +125°C. Symbol Parameter Input Level Input High Level 0.7*VDD Conditions Limit Units
Power Reset Threshold/Function (POR)
Symbol nPOR nPOR Threshold Parameter nPOR Power reset Buck1 Default Buck2 Percentage Target voltage Buck1 VBUCK1 VBUCK2 rising Buck2 VBUCK1 VBUCK2 falling Output Level Load Conditions 0.23 Units msec
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LM26480
Note Absolute Maximum Ratings indicate limits beyond which damage component occur. Operating Ratings conditions under which operation device guaranteed. Operating Ratings imply guaranteed performance limits. guaranteed performance limits associated test conditions, Electrical Characteristics. Note voltages with respect potential pin. Note Internal thermal shutdown circuitry protects device from permanent damage. Thermal shutdown engages 160°C (typ.) disengages 140°C (typ.) Note Human body model capacitor discharged through resistor into each pin. (MILSTD 3015.7) Note applications where high power dissipation and/or poor package thermal resistance present, maximum ambient temperature have derated. Maximum ambient temperature (TA-MAX) dependent maximum operating junction temperature (TJ-MAX-OP 125°C), maximum power dissipation device application (PD-MAX), junction-to-ambient thermal resistance part/package application (JA), given following equation: TA-MAX TJ-MAX-OP PD-MAX). Applications section. Note Junction-to-ambient thermal resistance highly application board-layout dependent. applications where high maximum power dissipation exists, special care must paid thermal dissipation issues board design. Note limits guaranteed design, test, statistical analysis. Typical numbers guaranteed, represent most likely norm. Note CIN, COUT: Low-ESR Surface-Mount Ceramic Capacitors (MLCCs) used setting electrical characteristics. Note device maintains stable, regulated output voltage without load. Note Dropout voltage voltage difference between input output which output voltage drops below nominal value. Note Quiescent current defined here difference current between input voltage source load VOUT. Note minimum line regulation values 1.8V. Note This specification guaranteed design. Note VOUT RDSON(P) (IOUT IRIPPLE). these conditions met, voltage regulation will degrade load increases. Note Pins operate from 1.74V 5.5V. This rating only series pass PMOS power FET. allows system design lower voltage rating input voltage comes from buck output. Note VPOR voltage which EPROM resets. This different from UVLO VINLDO12, which voltage which regulators shut off; also different from nPOR function, which signals regulators specified range.
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LM26480
Typical Performance Characteristics
Output Voltage Change Temperature (LDO1) 3.6V, VOUT 2.5V, load Output Voltage Change Temperature (LDO2) 3.6V, VOUT 1.8V, load
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Load Transient VIN, 2.5VOUT, load
Load Transient VIN, 2.5VOUT, 150-300 load
30040437 30040438
Line Transient (LDO1) VIN, VOUT, load
Line Transient (LDO2) VIN, 1.8VOUT, load
30040439
30040440
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LM26480
Enable Start-up time (LDO1) 0-3.6 VIN, VOUT, load
Enable Start-up time (LDO2) VIN, 1.8VOUT, load
30040441
30040442
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LM26480
Typical Performance Characteristics Buck
Shutdown Current Temp
2.8V 5.5V, 25°C Output Voltage Supply Voltage (VOUT 1.2V)
30040443 30040444
Output Voltage Supply Voltage (VOUT 2.0V)
Output Voltage Supply Voltage (VOUT 3.0V)
30040445
30040446
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LM26480
Typical Performance Characteristics Buck
mode Buck Efficiency Output Current (VOUT 1.2V,
Output Current transitions from mode
Efficiency Output Current (VOUT 2.0V,
30040447
30040448
Output Current transitions from mode mode Buck Efficiency Output Current (VOUT 3.0V, Efficiency Output Current (VOUT 3.5V,
30040449
30040450
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LM26480
Typical Performance Characteristics Buck
VIN= 3.6V, 25°C, VOUT 1.2V unless otherwise noted Load Transient Response VOUT 1.2V (PWM Mode) Mode Change Load Transients VOUT 1.2V (PWM PFM)
30040456
30040457
Line Transient Response 4.2V, VOUT 1.2V, load
Line Transient Response 3.6V, VOUT 3.0V, load
30040458
30040459
Start into Mode VOUT 1.2V, 1.5A load
Start into Mode VOUT 1.5A load
30040460
30040461
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LM26480
Start into Mode VOUT 1.2V, load
Start into Mode VOUT 3.0V, load
30040462
30040470
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LM26480
DC/DC Converters
OVERVIEW LM26480 provides DC/DC converters that supply various power needs application means linear dropout regulators, LDO1 LDO2, buck converters, SW2. table here under lists output characteristics various regulators. Supply Specification Output Supply Load IMAX VOUT Range Maximum Output Current (mA) 1500 1500
turns device, offering lowest current consumption. mode selected automatically mode forced through setting buck control register. Both operate 100% duty cycle (PMOS switch always drop control output voltage. this output voltage will controlled down lowest possible input voltage. Additional features include soft-start, under-voltage lock-out, current overload protection, thermal overload protection. CIRCUIT OPERATION DESCRIPTION buck converter contains control block, switching PFET connected between input output, synchronous rectifying NFET connected between output ground (BCKGND pin) feedback path. During first portion each switching cycle, control block turns internal PFET switch. This allows current flow from input through inductor output filter capacitor load. inductor limits current ramp with slope
LDO1 LDO2
analog analog digital digital
LINEAR DROPOUT REGULATORS (LDOs) LDO1 LDO2 identical linear regulators targeting analog loads characterized noise requirements. LDO1 LDO2 enabled through ENLDO pin.
storing energy magnetic field. During second portion each cycle, control block turns PFET switch off, blocking current flow from input, then turns NFET synchronous rectifier inductor draws current from ground through NFET output filter capacitor load, which ramps inductor current down with slope
output filter stores charge when inductor current high, releases when low, smoothing voltage across load.
30040404
NO-LOAD STABILITY LDOs will remain stable regulation with external load. This important consideration some circuits, example, CMOS keep-alive applications.
OPERATION During operation converter operates voltagemode controller with input voltage feed forward. This allows converter achieve excellent load line regulation. gain power stage proportional input voltage. eliminate this dependence, feed forward voltage inversely proportional input voltage introduced. INTERNAL SYNCHRONOUS RECTIFICATION While mode, buck uses internal NFET synchronous rectifier reduce rectifier forward voltage drop associated power loss. Synchronous rectification provides significant improvement efficiency whenever output voltage relatively compared voltage drop across ordinary rectifier diode. CURRENT LIMITING current limit feature allows converter protect itself external components during overload conditions. mode implements current limiting using internal comparator that trips 2.0A both bucks (typ). output shorted ground device enters timed current limit mode where NFET turned longer duration until inductor current falls below threshold, ensuring inductor current more time decay, thereby preventing runaway.
SW1, SW2: Synchronous StepDown Magnetic DC/DC Converters
FUNCTIONAL DESCRIPTION LM26480 incorporates high-efficiency synchronous switching buck regulators, SW2, that deliver constant voltage from single Li-Ion battery portable system processors. Using voltage mode architecture with synchronous rectification, both bucks have ability deliver 1500 depending input voltage output voltage (voltage head room), inductor chosen (maximum current capability). There three modes operation depending current required PWM, PFM, shutdown. mode handles current loads approximately higher, delivering voltage precision +/-3% with efficiency better. Lighter output current loads cause device automatically switch into reduced current consumption typ.) longer battery life. Standby operating mode
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LM26480
OPERATION very light loads, converter enters mode operates with reduced switching frequency supply current maintain high efficiency. part will automatically transition into mode when either conditions occurs duration more clock cycles: inductor current becomes discontinuous peak PMOS switch current drops below IMODE level
During operation, converter positions output voltage slightly higher than nominal output voltage during operation, allowing additional headroom voltage drop during load transient from light heavy load. comparators sense output voltage feedback control switching output FETs such that output voltage ramps between 0.8% 1.6% (typical) above nominal output voltage. output voltage below `high' comparator threshold, PMOS power switch turned remains until output voltage exceeds `high' threshold peak current exceeds level mode. typical peak current mode
Once PMOS power switch turned off, NMOS power switch turned until inductor current ramps zero. When NMOS zero-current condition detected, NMOS power switch turned off. output voltage below `high' comparator threshold (see following figure), PMOS switch again turned cycle repeated until output reaches desired level. Once output reaches `high' threshold, NMOS switch turned briefly ramp inductor current zero then both output switches turned part enters extremely power mode. Quiescent supply current during this `sleep' mode less than which allows part achieve high efficiencies under extremely light load conditions. When output drops below `low' threshold, cycle repeats restore output voltage ~1.6% above nominal output voltage. load current should increase during mode (see figure below) causing output voltage fall below `low2' threshold, part will automatically transition into fixed-frequency mode. SW1, CONTROL enabled/disabled through external enable pins. Modulation mode PWM/PFM default automatic depends load described above functional description. modulation mode factory trimmed, forcing buck operate mode regardless load condition.
30040405
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LM26480
SHUTDOWN MODE During shutdown PFET switch, reference, control bias circuitry converters turned off. NFET switch will shutdown discharge output. When converter enabled, soft start activated. recommended disable converter during system power under voltage conditions when supply less than 2.8V. SOFT START soft-start feature allows power converter gradually reach initial steady state operating point, thus reducing start-up stresses surges. LM26480 buck converters have soft-start circuit that limits in-rush current during start-up. During start-up switch current limit increased steps. Soft start activated only goes from logic logic high after reaches 2.8V. Soft start implemented increasing switch current limit steps both bucks (typ. switch current limit). start-up time thereby depends output capacitor load current demanded start-up. DROPOUT OPERATION LM26480 operate 100% duty cycle switching; PMOS switch completely dropout support
output voltage. this output voltage will controlled down lowest possible input voltage. When device operates near 100% duty cycle, output voltage ripple approximately minimum input voltage needed support output voltage VIN, ILOAD (RDSON, PFET RINDUCTOR) VOUT ILOAD RDSON, PFET RINDUCTOR Load current Drain source resistance PFET switch triode region Inductor resistance
FLEXIBLE POWER-ON RESET (i.e., POWER GOOD WITH DELAY) LM26480 equipped with internal Power-On-Reset ("POR") circuit which monitors output voltage levels bucks nPOR open drain logic output which logic when either buck outputs below rising value when both outputs fall below desired value. time delay between output voltage level nPOR enabled default. system designer choose external pull-up resistor (i.e. nPOR pin.
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LM26480
NPOR with Counter Delay
30040406
above diagram shows simplest application Power-On Reset, where both switcher enables tied together. Case causes nPOR transition triggers nPOR delay counter. power supply Buck2 does come within that period, nPOR will stay LOW, indicating power fail mode. Case indicates vice
versa scenario Buck1 supply come both cases nPOR remains LOW. Case shows typical application Power-On Reset, where both switcher enables tied together. Even RDY1 ramps slightly faster than RDY2 vice versa), nPOR signal will trigger programmable delay before going HIGH, explained below.
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LM26480
Faults Occurring Counter Delay After Startup
30040407
above timing diagram details Power Good with delay with respect enable signals EN1, EN2. RDY1, RDY2 internal signals derived from output comparators. Each comparator been trimmed follows: Comparator Level HIGH Buck Supply Level Greater than Less than
RDY1 signals High time then RDY1 signal rising edge triggers programmable delay counter ms). This delay forces nPOR between time interval NPOR then pulled high after programmable delay completed. RDY2 initiated during this interval nPOR signal ignores this event. either RDY1or RDY2 were then programmable delay triggered again.
circuits RDY1 symmetrical RDY2, each reference RDY1 will also work RDY2 vice versa.
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LM26480
NPOR Mask Window
30040408
Case that case where RDY2 initiated after triggered programmable delay. prevent nPOR being asserted again, masked window counter delay triggered rising edge. NPOR still held HIGH duration mask, whereupon nPOR status afterwards will depend status both RDY1 RDY2 lines. Case case where initiated after RDY1 triggered programmable delay, RDY2 never goes
HIGH (Buck2 never turns on). Normal operation operation nPOR occurs wilth respect RDY1, nPOR signal held HIGH duration mask window. that nPOR goes after masking window timed because dependent RDY1 RDY2, where RDY2 LOW.
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LM26480
Design Implementation Flexible Power-On Reset
30040409
Design implementation flexible power-on reset. internal power-on reset used with produce reset signal (LOW) delay timer nPOR. RDY1 RDY2 used generate signal (HIGH) delay timer. S=R=1 never occurs. mask timers triggered which gated with RDY1, RDY2 generate outputs final gate generate nPOR. UNDER VOLTAGE LOCK LM26480 features "under voltage lock circuit". function this circuit continuously monitor input
supply voltage (VINLDO12) automatically disables four voltage regulators whenever this supply voltage less than VDC. circuit incorporates bandgap based circuit that establishes reference used determine trip point detector. This signal then used gate enable signals four regulators LM26480. When VINLDO12 greater than four enables control four regulators, when VINLDO12 less than four regulators disabled detector being "Not state. circuit built hysteresis prevent chattering occurring.
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LM26480
Application Notes
EXTERNAL COMPONENT SELECTION
30040410
Ideal Resistor Values Target Vout
Common Values
Actual Actual VOUT VOUTDelta from Target Com/R 0.803 0.905 1.31 1.393 1.505 1.605 1.713 1.803 1.902 2.01 2.083 2.202 2.282 2.415 2.51 2.61 2.71 2.82 2.875 2.995 3.115 3.18 3.31 0.002 0.005 0.01 -0.008 0.005 0.005 0.013 0.003 0.002 0.01 -0.017 0.002 -0.018 0.015 0.01 0.01 0.01 0.02 -0.025 -0.005 0.015 -0.02 0.01
Feedback Capacitors C1(pF) C2(pF) none none none none none none none none none none none none none none none none none none none Buck1 Only Buck1 Buck2 Buck2 Only
output voltages bucks LM26480 established feed back resistor divider shown application circuit above. equation determining VOUT (R1+R2)/R2 where voltage Buck pin. Buck control loop will force voltage 0.50 above table shows ideal resistor values establish buck voltages from 0.8V along with common resistor val-
establish these voltages. Common resistors always produce target value, error given delta column. addition resistor feedback, capacitor feedback always required, depending output voltage capacitor also required. application diagram below above table these requirements.
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LM26480
Inductor LSW1,2
Value
Unit
Description SW1,2 inductor
Notes D.C.R.
OUTPUT INDUCTORS CAPACITORS There several design considerations related selection output inductors capacitors: Load transient response; Stability; Efficiency; Output ripple voltage; Over-current ruggedness. LM26480 been optimized with nominal values other values needed design, please contact National Semiconductor sales with concerns. INDUCTOR SELECTION nominal inductor value recommended. important guarantee inductor core does saturate during foreseeable operational situation. Care should taken when reviewing different saturation current ratings that specified different manufacturers. Saturation current ratings typically specified ratings maximum ambient temperature application should requested from manufacturer. There methods choose inductor saturation current rating: Recommended method: best guarantee inductor does saturate choose inductor that saturation current rating greater than maximum LM26480 current limit 2.4A. this case device will prevent inductor saturation. Alternate method: recommended approach cannot used, care must taken guarantee that saturation current greater than peak inductor current:
ISAT exceeded during operation, including transients, startup, high temperature, worst case conditions, etc. SUGGESTED INDUCTORS THEIR SUPPLIERS Model Vendor Dimension (mm) ISATURATION (max)
DO3314-22 Coilcraft
1.8A 1.3A 2.2A 1.9A 1.5A
LPO3310-2 Coilcraft 22MX ELL6PG2R Panaso ELC6GN2R Panaso CDRH2D14 Sumida NP-2R2NC
Note: Inductor Current Saturation values estimates; inductor manufacturer should contacted guaranteed values.
OUTPUT CAPACITOR SELECTION ceramic output capacitor 6.3V recommended with about less. Output ripple estimated from vector reactive (Capacitor) voltage component real (ESR) voltage component output capacitor.
VCOUT: VROUT: VPPOUT:
Estimated reactive output ripple Estimated real output ripple Estimated peak-to-peak output ripple
30040471
ISAT:
Inductor saturation current operating temperature ILPEAK: Peak inductor current during worst case conditions IOUTMAX: Maximum average inductor current IRIPPLE: Peak-to-Peak inductor current VOUT: Output voltage VIN: Input voltage Inductor value Henries IOUTMAX Switching frequency, Hertz Estimated duty factor EFF: Estimated power supply efficiency
output capacitor needs mounted close possible output device. better temperature performance, types recommended. bias characteristics ceramic capacitors must considered when selecting case sizes like 0805 0603. bias characteristics vary from manufacturer manufacturer case size. bias curves should requested from them part capacitor selection process. typically higher smaller packages. output filter capacitor smooths current flow from inductor load, helps maintain steady output voltage during transient load changes reduces output voltage ripple. These capacitors must selected with sufficient capacitance sufficiently perform these functions. Note that output voltage ripple dependent inductor current ripple equivalent series resistance output capacitor (ESRCOUT). ESRCOUT frequency dependent well temperature dependent. RESR should calculated with applicable switching frequency ambient temperature.
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LM26480
INPUT CAPACITOR SELECTION required ceramic input capacitor least 6.3V with under input power source supplies average current continuously. During PFET switch on-time, however, demanded di/dt higher than typically supplied input power source. This delta supplied input capacitor. simplified "worst case" assumption that PFET current supplied input capacitor. This will result conservative estimates input ripple voltage capacitor current. Input ripple voltage estimated follows:
VPPIN: IOUT: CIN: ESRIN:
Estimated peak-to-peak input ripple voltage Output current, Amps Input capacitor value, Farads Input capacitor ESR, Ohms
This capacitor exposed significant current, important select capacitor with adequate current rating. Capacitor current estimated follows:
IRSCIN
Estimated input capacitor current
Model C2012X5R0J475K JMK212BJ475K GRM21BR60J475K C1608X5R0J475K COUT GRM21BR60J106K JMK212BJ106K C2012X5R0J106K C1608X5R0J106K
Type Ceramic, Ceramic, Ceramic, Ceramic, Ceramic, Ceramic, Ceramic, Ceramic,
Vendor Taiyo-Yuden Murata Murata Taiyo-Yuden
Voltage Rating 6.3V 6.3V 6.3V 6.3V 6.3V 6.3V 6.3V 6.3V
Case Size 0805, (2012) 0805, (2012) 0805, (2012) 0603, (1608) 0805, (2012) 0805, (2012) 0805, (2012) 0603, (1608)
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LM26480
FEEDBACK RESISTORS LDOs
30040410
Target VOUT
Ideal Resistor Values 1000 1040 1080 1120 1160 1200
Common Values 1100 1150 1210 1000 1000 1000 1210 1210 1210
Actual VOUT Com/R 1.31 1.393 1.505 1.605 1.711 1.802 1.905 2.01 2.118 2.203 2.283 2.412 2.505 2.614 2.709 2.809 2.873 3.118 3.174 3.314 3.381 3.525
output Voltages LDOs LM26480 established feed back resistor divider shown application circuit above. equation determining VOUT VOUT VFB(R1+R2)/R2, where voltage LDOX_FB pin. control loop will force voltage VFBo 0.50 above table shows ideal resistor values
tablish voltages from along with common resistor values establish these voltages. Common resistors always produce target value, error given final column. keep power consumed feedback network recommended that established about Lesser values users discretion.
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LM26480
CAPACITOR SELECTION Input Capacitor input capacitor required stability. recommended that capacitor connected between input ground (this capacitance value increased without limit). This capacitor must located distance more than from input returned clean analog ground. good quality ceramic, tantalum, film capacitor used input. Important: Tantalum capacitors suffer catastrophic failures surge currents when connected impedance source power (like battery very large capacitor). tantalum capacitor used input, must guaranteed manufacturer have surge current rating sufficient application. There requirements input capacitor, tolerance temperature coefficient must considered when selecting capacitor ensure capacitance will remain approximately over entire operating temperature range. Output Capacitor LDOs LM26480 designed specifically work with very small ceramic output capacitors. ceramic capacitor (temperature types Z5U, X7R) with between suitable application circuit. also possible tantalum film capacitors device output COUT VOUT), these attractive reasons size cost. output capacitor must meet requirement minimum value capacitance also have value that within range stability. Capacitor Characteristics LDOs designed work with ceramic capacitors output take advantage benefits they offer. capacitance values range 0.47 ceramic capacitors smallest, least expensive have lowest values, thus making them best eliminating high frequency noise. typical ceramic capacitor range which easily meets requirement stability LDOs. both input output capacitors, careful interpretation capacitor specification required ensure correct device operation. capacitor value change greatly, depending operating conditions capacitor type. particular, output capacitor selection should take account capacitor parameters, ensure that specification within application. capacitance vary with bias conditions well temperature frequency operation. Capacitor values will also show some decrease over time aging. capacitor parameters also dependent particular case size, with smaller sizes giving poorer performance figures general. example, graph below shows typical graph comparing Capacitor CLDO1 CLDO2 CSW1 CSW2 Value 0.47 0.47 Unit
different capacitor case sizes capacitance bias plot.
30040416
shown graph, increasing bias condition result capacitance value that falls below minimum value given recommended capacitor specifications table. Note that graph shows capacitance spec 0402 case size capacitor higher bias voltages. therefore recommended that capacitor manufacturers' specifications nominal value capacitor consulted conditions, some capacitor sizes (e.g. 0402) suitable actual application. ceramic capacitor's capacitance vary with temperature. capacitor type X7R, which operates over temperature range -55°C +125°C, will only vary capacitance within ±15%. capacitor type similar tolerance over reduced temperature range -55°C +85°C. Many large value ceramic capacitors, larger than manufactured with temperature characteristics. Their capacitance drop more than temperature varies from 25°C 85°C. Therefore recommended over applications where ambient temperature will change significantly above below 25°C. Tantalum capacitors less desirable than ceramic output capacitors because they more expensive when comparing equivalent capacitance voltage ratings 0.47 range. Another important consideration that tantalum capacitors have higher values than equivalent size ceramics. This means that while possible find tantalum capacitor with value within stable range, would have larger capacitance (which means bigger more costly) than ceramic capacitor with same value. should also noted that typical tantalum will increase about temperature goes from 25°C down -40°C, some guard band must allowed. Recommended Type
Description
LDO1 output capacitor Ceramic, 6.3V, LDO2 output capacitor Ceramic, 6.3V, output capacitor output capacitor Ceramic, 6.3V, Ceramic, 6.3V,
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LM26480
Analog Power Signal Routing
power inputs should tied main source (i.e. battery), unless user wishes power from another source. (i.e. powering from Buck output). analog inputs power internal bias error amplifiers, they should tied main VDD. analog inputs must have input voltage between specified Electrical Characteristics section this datasheet. other Vins (VINLDO1, VINLDO2, VIN1, VIN2) actually have inputs lower than 2.8V, long it's higher than
programmed output (+0.3V, safe). analog digital grounds should tied together outside chip reduce noise coupling. more information board layout techniques, refer Application Note AN-1187 "Leadless Lead frame Package (LLP)." http://www.national.com This application note also discusses package handling, solder stencil assembly process.
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LM26480
Board Layout Considerations
board layout important part DC-DC converter design. Poor board layout disrupt performance DCDC converter surrounding circuitry contributing EMI, ground bounce, resistive voltage loss traces. These send erroneous signals DC-DC converter
sulting poor regulation instability. Poor layout also result re-flow problems leading poor solder joints, which result erratic degraded performance. Good layout LM26480 bucks implemented following simple design rules, illustrated Figure
30040468
FIGURE Board Layout Design Rules LM26480 Place buck inductor filter capacitors close together make trace short. traces between these components carry relatively high switching currents antennas. Following this rule reduces radiated noise. Place capacitors inductor close buck. Arrange components that switching current loops curl same direction. During first halt each cycle, current flows from input filter capacitor, through buck inductor output filter capacitor back through ground, forming current loop. second half each cycle, current pulled from ground, through buck inductor, output filter capacitor then back through ground, forming second current loop. Routing these loops current curls same direction prevents magnetic field reversal between half-cycles reduces radiated noise. Connect ground pins buck, filter capacitors together using generous component-side copper fill pseudo-ground plane. Then connect this groundplane used) with several vias. This reduces ground-plane noise preventing switching currents from circulating through ground plane. also reduces ground bounce buck giving lowimpedance ground connection. wide traces between power components power connections DC-DC converter circuit. This reduces voltage errors caused resistive losses across traces Rout noise sensitive traces, such voltage feedback path, away from noisy traces between power components. voltage feedback trace must remain close buck circuit should routed directly from VOUT output capacitor should routed opposite noise components. This reduces radiated onto DC-DC converter's voltage feedback trace. mobile phones, example, common practice place DC-DC converter corner board, arrange CMOS digital circuitry around (since this also generates noise), then place sensitive preamplifiers stages diagonally opposing corner. Often, sensitive circuitry shielded with metal power postregulated reduce conducted noise, using low-dropout linear regulators.
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LM26480
High VIN-High Load Operation
Additional inforamtion provided when operated extremes regulator loads. These described terms junction temperature buck output ripple management. Junction Temperature maximum junction temperature TJ-MAX-OP 125°C package. following equations demonstrate junction temperature determination, ambient temperature TA-MAX total chip power controlled keep below this maximum: TJ-MAX-OP TA-MAX (JA) [°C/Watt] (PD-MAX) [Watts] Total power dissipation PD-MAX individual power dissipation four regulators plus minor amount chip overhead. Chip overhead bias, analog. PD-MAX PLOD1 PLDO2 +PBUCK1 PBUCK2 (0.0001A VIN) [Watts].
Power dissipation LDO1 (PLDO1) (VINLDO1 VOUTLDO1) IOUTLDO1 [V*A] Power dissipation LDO2 (PLDO2) (VINLDO2 VOUTLDO2) IOUTLDO2 [V*A] Power dissipation Buck1 (PBuck1) POUT VOUTBUCK1 IOUTBUCK1 [V*A] efficiency Buck1 Power dissipation Buck2 (PBuck2) POUT VOUTBUCK2 IOUTBUCK2 [V*A] efficiency Buck2 Where efficiency specific condition taken from efficiency graphs. ILOADincrease, output ripple associated with Buck Regulators also increases. This mainly occurs with 5.2V load current greater than 1.20A. ensure operation this area operation, recommended that system designer circumvents output ripple issues installing Schottky diodes bucks(s) that expected perform under these extreme conditions.
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LM26480
Physical Dimensions inches (millimeters) unless otherwise noted
24-Pin Package Package SQA24A ordering, refer Ordering Information table
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LM26480Externally Programmable Dual High-Current Step-Down DC/DC Dual Linear Regulators
Notes
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LM26480 Externally Programmable Dual High-Current Step-Down DC/DC Dual

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