LM5071 Evaluation Board National Semiconductor Application Note 1
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LM5071 Evaluation Board
LM5071 Evaluation Board
National Semiconductor Application Note 1430 Youhao April 2006
LM5071 evaluation board designed provide cost, fully IEEE 802.3af compliant Power over Ethernet (PoE) power supply, capable operating with both auxiliary (AUX) power sources. evaluation board features LM5071 Powered Device (PD) interface controller integrated circuit (IC) configured versatile flyback topology.
former converter efficiency: Overall efficiency (including diode bridge): 81.5%
Features LM5071 Evaluation Board:
Single Isolated 3.3V output Dual Isolated 3.3V outputs supported (see Figure Maximum output current 3.3A Input voltage range (full power): With installed wide-voltage-range EP13 transformer input voltage range: input voltage range: With optional, efficiency-optimized EP13 transformer input voltage range: input voltage range: Measured maximum efficiency: With installed wide-voltage-range EP13 transformer converter efficiency: Overall efficiency (including diode bridge): 78.5% With optional, efficiency-optimized EP13 trans-
This application note focuses evaluation board. Please refer datasheet detailed information about complete functions features LM5071
Board Size: 2.75 2.00 0.66 inches Operating frequency: Programmed input under-voltage lockout (UVLO) release: Nominal Programmed input UVLO hysteresis: 5.9V
Note about Input Potentials
LM5071 designed applications that typically -48V systems, which notations -48V normally refer high input potentials, respectively. However, easy readability, LM5071 datasheet written positive voltage convention with positive input potentials referenced LM5071. Therefore, when testing evaluation board with bench power supply, negative terminal power supply equivalent system's -48V potential, positive terminal equivalent system ground. prevent confusion between datasheet this application note, same positive voltage convention used herein.
Schematic Evaluation Board
Figure shows schematic LM5071 evaluation board. Appendix Bill Materials (BOM).
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2006 National Semiconductor Corporation
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Schematic Evaluation Board
FIGURE Schematic LM5071 Evaluation Board
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Connection Proper Test Methods
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FIGURE LM5071 Evaluation Board Connections Figure shows connections LM5071 evaluation board. LM5071 evaluation board three ports connections. RJ45 receptacle connector input, PJ102A power jack input (also accessible with posts located right behind jack), 3.3V output port accessible with posts input, diode bridges steer current positive negative supply pins LM5071. input, high potential input voltage should feed into center PJ102A jack. output connection, load either passive resistor active electronic load. Attention should paid output polarity when connecting electronic load. additional filter capacitors greater than total across output port recommended unless feedback loop compensation adjusted accordingly. Sufficiently large wire size smaller than required when connecting source supply load. Also, monitor current into unit under test. Monitor voltages directly board terminals, resistive voltage drops along connecting wires decrease measurement accuracy. Never rely supply voltmeter accurate efficiency measurements needed. When measuring dc-dc converter efficiency, converter input voltage should measured across this input converter stage. When measuring evaluation board overall efficiency, both input output voltage should read from terminals evaluation board.
Loading Current Limiting Behavior
resistive load optimal, appropriate electronic load specified operation down 2.0V acceptable. maximum load current 3.3A. Exceeding this current input voltage cause oscillatory behavior part will into current limit mode. Current limit mode triggered whenever current through connector exceeds 390mA (nominal). current limit triggered, switching regulator automatically disabled discharging softstart capacitor through pin. module then allowed restart, unit will operate automatic re-try (hiccup) mode long over-current condition remains.
Power
suggested apply power first. During first power load should kept reasonably low. Verify supply current during signature classification modes before applying full power. During signature mode, module should have characteristics resistor series with diodes. During classification mode, current draw should about RCLASS left open, defaulting class proper response observed during both signature classification modes, check connections closely. current flowing likely that conductors feeding power have been incorrectly installed. Once proper setup been established, full power applied. voltmeter across output terminals (+3.3V) (3.3V RTN), will allow direct measurement 3.3V output line. Because output voltage isolated, should measured meter referenced bench power supply ground. 3.3V output voltage observed within seconds, turn power supply review connections. final check efficiency best confirm that unit operating properly. Efficiency significantly lower than full load indicates problem. After operation verified, apply power. recommended that application power follow same precautions that PoE. output voltage
Source Power
fully test LM5071 evaluation board, power supply capable least required input. source power, power supply capable 1.5A. output over-voltage overcurrent limit features bench power supplies protect board against damage errant connections.
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Power
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observed, likely that power feed polarity reversed. After successful operation observed, full power testing begin.
equivalent signature impedance 25.1k, which valid signature range 23.75 26.25 IEEE 803.2af. should noted that when power present, will allow PoE's power sourcing equipment (PSE) identify valid device, because voltage will cause front-end current steering diode bridges reverse biased during detection mode. This prevents from applying power, evaluation board only draws current from source.
Interface Operating Modes
When connecting into system, evaluation board's Powered Device interface will through following operating modes sequence: signature detection, power level classification (optional), application full power. Refer LM5071 datasheet IEEE 802.3af detailed information about these operating modes.
Classification
classification implemented with R22. evaluation board default Class leaving RCLASS open (R22 position populated). activate specific class instead Class install according following table. ICLASS(MIN) 17mA 26mA 36mA ICLASS(MAX) 12mA 20mA 30mA 44mA Selection Open 82.5 53.6 38.3
Signature Detection
evaluation board, signature implemented with R13. 26.1 resistor yields Class PMIN 0.44W 0.44W 3.84W 6.49W Reserved PMAX 12.95W 3.84W 6.49W 12.95W Reserved
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Input UVLO UVLO Hysteresis
input UVLO threshold UVLO hysteresis independently programmed selecting R37. UVLO release threshold level mainly determined ratio governed following equation,
where stands forward voltage drop single diode input current steering bridge. UVLO hysteresis determined following equation: UVLO_hysteresis 10µA evaluation board uses 33.2 setting UVLO release threshold about UVLO hysteresis 5.9V. helps filter input voltage transients, thus preventing faulty activation release input UVLO.
55°C maximum junction temperature these devices, which true most applications. 55°C, selection S3BB-13 CRH01 CMHD4448 CMPT5401 will cause false signal pin. When designing higher temperature requirement some particular application, values R19, R23, should chosen such that voltage created across does exceed 0.5V during operation. reverse protected, additional reverse blocking diode will required complete auxiliary input reverse protection.
Flyback Converter Topology
dc-dc converter stage LM5071 evaluation board features flyback topology, which employs minimum number power components implement isolated power supply lowest possible cost. unique characteristic flyback topology power transformer. Unlike ordinary power transformer that simultaneously transfers power from primary secondary, flyback transformer first stores energy transformer core every switching cycle when main switch turned then releases stored energy load during rest cycle. When stored energy completely released before main switch turned again, said that flyback converter operates continuous conduction mode (CCM). Otherwise, discontinuous conduction mode (DCM). Major advantages over include lower ripple current ripple voltage, requiring smaller input output filter capacitors; (ii) lower current, thus reducing conduction losses. keep flyback converter light load, transformer's primary inductance should designed large practical. Major drawbacks CCM, compared DCM, presence Right-Half-Plane Zero which limit achievable bandwidth feedback loop; (ii) need slope compensation stabilize feedback loop duty cycles greater than 50%. flyback topology have multiple secondary windings multi output channels. more these secondary channels normally utilized internally converter itself provide necessary bias voltages controller other devices. evaluation board uses small power transformer having primary inductance This compromise made allow small transformer operate over wide input voltage range from 60V. However, with this transformer, flyback converter runs full load input voltages lower than 42V, higher input voltages light loads. LM5071's built-in slope compensation helps stabilize feedback loop when duty cycle exceeds input voltage range. transformer winding used provide bias voltage (VCC) LM5071 Although LM5071 controller includes internal startup regulator which support bias requirement indefinitely, transformer winding produces about higher than startup regulator output, thus shutting startup regulator reducing power dissipation inside
Power Option
power option, circuitry tied forces UVLO release order allow operation voltage 10.5V (9.5V seen LM5071 IC). Note that references while auxiliary supply references RTN, which will different diode drop until internal swap MOSFET engaged. required that installed when input lower than 14V. This will bypass internal startup regulator directly supply bias voltage LM5071 startup. CMHD4448 equivalent When switching circuit establishes stable operation, will provided transformer winding with level 16V. This voltage damage internal startup regulator back feeding lower potential line. solve this problem, introduced protect bypassing back feed path clamping pin. evaluation board, already been installed. However, applications where input voltage always higher than 18V, removed save cost. Small value resistors series with auxiliary input limit inrush current from auxiliary supply. They should made large practical given design constraints. Special attention should paid selection They should leakage current devices. Otherwise leakage current during operation will create false signal circuit powered from source. Most diode transistor datasheets provide information maximum leakage current both 25°C 125°C, although data intermediate temperatures often given. approximated that leakage current doubles every 10°C temperature rise. junction temperature these devices should reach 125°C because only dissipation inside these devices leakage current. Therefore necessary select devices based maximum leakage current specified 125°C. evaluation board design considered
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Factors Limiting Minimum Operating Input Voltage
LM5071 capable operating with power source 10.5V (after input OR-ing-diode drop, sees 9.5V). However, minimum operating input voltage evaluation board full load mainly determined factors; flyback power transformer design values current sense resistors R15. installed EP13 type power transformer (DA2257-AL DCT13EP-U12S005) cost solution operate with wide input voltage range. However, small crosssectional area EP13 magnetic core limits maximum flux handle. such small transformer from under full load condition, compromise between minimum operating input voltage maximum inductance transformer must made such that peak current input will cause peak flux density exceed 3000 Gauss. drawback this cost solution that currents flowing through dc-dc converter stage increased efficiency dc-dc converter reduced about Replacing originally installed transformer with optional power transformer DA2383-AL from Coilcraft improves efficiency, minimum operating input voltage will limited 24V. this optional transformer lower input voltage, load level should scaled down accordingly, shown Figure where Dmax duty cycle minimum input voltage switching frequency, flyback transformer primary inductance, transformer's primary secondary turns ratio output voltage, volts forward drop output diode volts Selecting 0.30 both will allow minimum operating voltage 14V. lower input voltage, Dmax greater hence must reduced accordingly. However, smaller resistors increase slope compensation. Increasing slope compensating makes feedback loop appear more like voltage mode than current mode which requires capacitor rather than cost capacitor initially installed evaluation board. summary, minimum operating input voltage evaluation board limited cost solution. order evaluation board with lower source, power transformer output capacitor C16, should modified addition installation
Performance Characteristics
POWER SEQUENCE high level integration designed into LM5071 allows power sequencing communications occur within Very little system management design required user. power sequence follows. Note that isolated from +3.3V output board: Before power nodes non-isolated section power supply remain high potential until UVLO released drain internal swap MOSFET pulled down Once drops below 1.5V (referenced VEE), regulator released allowed start. This signals assertion internal "Power Good" signal. regulator ramps rate equal current limit, typically divided load capacitance, C19. Once regulator within minimum regulation, about 7.6V referenced RTN, soft-start released. soft-start will rise rate equal soft-start current source, typically 10µA, divided soft-start capacitance, C26. switching regulator achieves regulation, auxiliary winding will raise voltage about 10V, thus shutting down internal regulator increasing efficiency. Figure shows voltages RTN, VCC, (Softstart) pins, referenced pin, during normal startup sequence. more detailed scope plot regulator starting given Figure auxiliary winding starts supply higher voltage switching regulator output voltage rises.
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FIGURE Maximum Load Current Minimum Input Voltage Limited Different EP13 Type Power Transformers optimize efficiency over maximum input voltage range 9.5V 60V, larger magnetic core like EFD20 should used. EFD20 core adequate cross-sectional area handle peak currents 9.5V input. effects current sense resistors also limit minimum input operating voltage. LM5071's internal slope compensation stabilizes feedback loop dc-dc converter when duty cycle exceeds input voltages lower than 22V. However, relative magnitude slope compensation inversely proportional values R15. maximum values governed following relation:
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Performance Characteristics
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Horizontal Resolution: ms/Div.
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Trace +3.3V output voltage, 1V/Div. Trace Softstart pin, 1V/Div. Trace Input current coupled), mA/Div. FIGURE Regulator Output (+3.3V) Startup Detail OUTPUT DEAD SHORT FAULT RESPONSE evaluation board survives output dead short condition running into re-try mode (hiccups). Applying dead short +3.3V line causes number protection mechanisms occur sequentially. They are: Feedback raises duty cycle attempt maintain output voltage. This initiates cycle-by-cycle over-current limiting which turns main switch when current sense (CS) exceeds current limit threshold. average current internal interface MOSFET rises until current limited around Some overshoot current will observed, takes time current limit amplifier react change operating mode MOSFET. Because linear current limit accomplished driving MOSFET into saturation region, drain voltage (RTN pin) rises. When reaches 2.5V with respect VEE, internal power good signal de-asserted.
Horizontal Resolution: ms/Div. Trace pin, elevated until UVLO release. 5V/Div. Trace pin, starts when achieves minimum regulation. 5V/Div. Trace VCC, starts when 1.5V, elevated auxiliary winding. 5V/Div. FIGURE Normal Startup Sequence
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Horizontal Resolution: ms/Div. Trace pin, elevated until UVLO release. 5V/Div. Trace Vout, cross-regulate after output regulation established. 1V/Div. Trace VCC, starts when 1.5V, elevated auxiliary winding. 2V/Div. FIGURE Startup Detail Figure shows normal 3.3V line startup, along with softstart reference.
de-assertion power good causes discharge soft-start capacitor, which disables switching action dc-dc converter. Once switching stops, current internal MOSFET will decrease drain voltage will fall back below 1.5V with respect VEE. When power good re-asserted, dc-dc converter will automatically restart with soft-start sequence. re-try mode shorted output condition observed Figure soft-start observed rise quickly LM5071 reacts fault. This because references RTN, while scope measurements reference VEE.
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Performance Characteristics
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RIPPLE VOLTAGE/CURRENT Figure shows output ripple voltage input ripple current input voltage 3.3A output.
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Horizontal Resolution: ms/Div. Trace LM5071 1V/Div. Trace Softstart pin, 2V/Div. Trace Test board input current, mA/Div. FIGURE Shorted Output Fault Condition Automatic Re-try STEP RESPONSE Figure shows step load response 48V.
Horizontal Resolution: ms/Div. Trace Output voltage coupled), mV/Div. Trace Input current coupled), mA/Div. FIGURE Ripple Currents Voltages FLYBACK TRANSFORMER WAVEFORMS Figure Figure show typical drain source voltage main switch reverse voltage rectifier diode respectively, input voltage 3.3A output.
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Horizontal Resolution: µs/Div. Trace Output voltage coupled), mV/Div. Trace Output current coupled), 0.5A/Div. FIGURE Regulator Response Step Load
Horizontal Resolution: µs/Div. Trace Drain source voltge main switch 50V/Div. FIGURE Flyback Main Switch Drain Voltage Waveform
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Performance Characteristics
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reduce cost. Reconfiguration circuit board non-isolated version accomplished following four steps (refer Figure indicated otherwise): Delete unused parts from circuit board well BOM: C20, C22, C25, C28, R11, R16, R17, R24, Connect test points with wire (refer Figure 13). Short pads installing resistor R2010 size, soldering piece wire. Change Figure shows schematic non-isolated circuit single 3.3V output. Similar changes also apply dual output version.
Enhancing Input Filter Performance
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Horizontal Resolution: µs/Div. Trace Reverse voltage across output rectifier diode 5V/Div. FIGURE Output Rectifier Reverse Voltage Waveform
Reconfiguration Evaluation Board 3.3V Dual Outputs
standard evaluation circuit easily reconfigured into 3.3V 0.6A 5.5V, dual output power supply. reconfiguration needs populate components 5.5V output rail, shown Figure These components listed additional list Appendix.
Reconfiguration Evaluation Board Non-Isolated Output Applications
applications where output isolation required, non-isolated version evaluation board used
evaluation board employs ceramic capacitors input filter DC-DC converter stage. configuration adequate meet IEEE 802.3af specifications, though required further enhance input filter performance considerations. inductor such Coilcraft DO3308P-103MLD added. inductor should installed location side Board, location originally shorted with wire. Also, install aluminum electrolytic capacitor such Panasonic EEV-HA2A220P location right beside side Board order protect LM5072 absorbing inductor energy during shutdown. jumper wire thicker with insulation sleeve should soldered connect junction with junction R27. doing capacitor placed front directly across pins LM5072. cost consideration, ceramic capacitor (4.7 deleted from PCB, will adequate attenuate input ripple current below peak peak
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FIGURE Schematic Dual Outputs
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FIGURE Schematic Non-Isolated Output
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Note Using Efficiency Optimized EP13 Power Transformer DA2383
Please note that DA2383 single output transformer. When using DA2383 obtain better efficiency (See Figure applicable load input voltage levels), should removed installed onto pads side evaluation board. This because secondary winding DA2382 uses Pins through transformer bobbin, unlike DA2257 that only uses Pins secondary winding. maximum converter stage efficiency 3.3A will expected greater than 84%.
More Hints Improving Efficiency
Since evaluation board designed cost solution, upgrading following components with slightly more expensive devices will increase efficiency. SUD15N15-95 faster device than installed SUD25N15-52, improve dc-dc converter efficiency (ii) DFLS1100 100V high voltage Schottky barrier rectifier with leakage current, increase operation's end-to-end efficiency least This suitable input voltage greater than 15V.
Appendix: LM5071 Evaluation Board Bill Materials
ITEM PART NUMBER CBRHD-01 CBRHD-01 C0805C473K5RAC C0805C681K5RAC C5750X7R2A475M C5750X7R2A475M C3216X5R0J106M C3216X5R0J106M C3216X5R0J106M C3216X5R0J106M C3216X5R0J106M EMVY6R3ADA331MF80G C2012X7R1E105K C2012X7R1E474K C0805C102K5RAC C0805C102K5RAC C0805C331K5RAC C0805C473K5RAC C2012X7R2A104K C4532X7R3D222k C0805C473K5RAC S3BB-13 CRH01 CMHD4448 12CWQ03FN CMR1U-01M RJ-45-8N-B PJ-102A 3104-2-00-01-00-00-080 3104-2-00-01-00-00-080 bus-wire short DO1813P-331MLD 5012K-ND 5012K-ND SUD25N15-52 CMPT5401 DESCRIPTION DIODE BRIDGE, SMDIP, CENTRAL DIODE BRIDGE, SMDIP, CENTRAL CAP, CER, CC0805, KEMET CAP, CER, CC0805, KEMET CAPACITOR, CER, CC2220, CAPACITOR, CER, CC2220, CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, ELEC, CHEMI-ON CAPACITOR, CER, CC0805, CAPACITOR, CER, CC0805, CAP, CER, CC0805, KEMET CAP, CER, CC0805, KEMET CAP, CER, CC0805, KEMET CAP, CER, CC0805, KEMET CAPACITOR, CER, CC0805, CAPACITOR, CER, CC1812, CAP, CER, CC0805, KEMET SCHOTTKY, SMB, DIODE ONLY INSTALL SCHOTTKY, DO123, TOSHIBA DIODE, DO123, CENTRAL SCHOTTKY, TO252, ULTRAFAST DIODE, CENTRAL RJ-45 CONNECTOR POWER JACK POST, MILL POST, MILL WIRE INDUCTOR, COILCRAFT TEST POINT, KEYSTONE TEST POINT, KEYSTONE MOSFET, N-CH, TO252, VISHAY BIPOLAR, PNP, SOT23, CENTRAL 150V, 150V, 0.33µH 200V 125mA, 12A, 100V VALUE 0.5A, 100V 0.5A, 100V 47nF, 680p, 4.7µF, 100V 4.7µF, 100V 10µF, 6.3V 10µF, 6.3V 10µF, 6.3V 10µF, 6.3V 10µF, 6.3V 330µF, 6.3V 1.0µF, 0.47µF, 1nF, 1nF, 330pF, 47nF, 100nF, 100V 2.2nF, 47nF, 100V
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Appendix: LM5071 Evaluation Board Bill Materials
ITEM PART NUMBER CRCW2512100J CRCW2512100J CRCW120649R9F CRCW 120610R0F CRCW08055903F CRCW08051001F CRCW080510R0F CRCW08051000F CRCW08051002F CRCW08052432F CRCW08052612F CRCW12060R301F CRCW12060R301F CRCW08051001F CRCW08051001F CRCW08051472F CRCW08052003F CRCW08056340F CRCW08052432F CRCW08051003F CRCW08050R0J CRCW08050R0J CRCW08053320F CRCW08052742F CRCW08052742F CRCW08053322F DA2257-AL DCT13EP-U12S005 LM5071-80 PC3H7D PS2801-1-L LMV431A CMZ5499B SMAJ58A ZENER, 62V, CENTRAL AVS, 58V, DIODE OPTO-COUPLER, SHARP OPTIO-COUPLER, RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR OPTIONAL CLASS RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR RESISTOR DESCRIPTION
(Continued) VALUE 49.9 24.3k 26.1k 0.301 0.301 14.7k 200k 24.3k 100k 27.4k 27.4k 33.2k
XFMR, DUAL OUTPUT FLYBACK, EP13, COILCRAFT XFMR, DUAL OUTPUT FLYBACK, EP13,
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LM5071 Evaluation Board
Additional 5.5V Output Rail
ITEM PART NUMBER C3216X5R1A106M C3216X5R1A106M C3216X5R1A106M EMVY100ADA101MF55G CMSH2-60 3104-2-00-01-00-00-080 3104-2-00-01-00-00-080 DO1813P-181MLD CMZ5920B DESCRIPTION CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, CER, CC1206, CAPACITOR, ELEC, CHEMI-ON DIODE, SMA, CENTRAL POST, MILL POST, MILL INDUCTOR, COILCRAFT ZENER, SMA, CENTRAL 0.18µH 6.2V VALUE 10µF, 10µF, 10µF, 100µF,
Note: total load dual outputs should limited below maximum.
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