LM5020 Reference Design -Dual Output FlybackConverter with isolatedoutputs of 5V@0.2A and12V@2.1A. Two LM2736Y'sprovide an additional outputof 3.3V@0.5A and 5V@0.5A.

National SemiconductorLM5020Power Applications Design Center, AmericasMay 2007

1.0 Design Specifications

Inputs Output #1 Output #2 Output #3 Output #4

VinMin=9V Vout1=5V Vout2=12V Vout3=3.3V Vout4=5V

VinMax=42V Iout1=0.2A Iout2=2.1A Iout3=0.5A Iout4=0.5A

2.0 Design DescriptionThis design utilizes the LM5020 Current Mode PWM Con-troller configured in a dual output Flyback converter. Thisisolated design operates at 300kHz and uses a custom trans-former to convert the input voltage, via flyback action, to anoutput voltage level of 12V at 2.1A, as well as produce anisolated 5V@0.2A rail. The relative low output power of thisdesign, and the fact that V cc is not required to power addi-tional IC’s, allows the primary bias winding to be connectedto V in . The LM5020 has a minimum input voltage of 13V soa start-up bias circuit was added to apply an external voltageto V cc until the input voltage reached the proper thresholdlevel.

With total potential output power less than 30W, a customEFD20 core was chosen for this design. Because of the input

voltage range, a CCM to DCM transition tradeoff was madeto minimize losses associated with DCM operation. RadiatedEMI requirements necessitated the use of snubbers and otherfiltering elements to minimize high energy signals from inter-fering with adjacent circuitry.

The 12V rail also fed a 5V@0.5A rail, as well as an optional3.3V@0.5A rail. The secondary side feedback componentsare selected appropriately to ensure the voltage regulationremains solid and that proper gain and phase margins aremaintained for stable operation and quick transient response.

© 2007 National Semiconductor Corporation www.national.com

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4.0 Bill of Materials

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LM

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NSC0607 LM5020/LP2992/LM2736 - Vin=9-42V,Flyback Converter: Vout =5V(I)@0.2A, 12V@2.1A w/ 5V@0.5A; and optional 3.3V@0.5A Buck Converter 12-13-2005

Designator Part Type Footprint Description ManufacturerC1 OPENC10 100pF 805 Capacitor Ceramic X7R Vitramon/VJ0805C11 100pF 805 Capacitor Ceramic X7R Vitramon/VJ0805C12 0.1uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C13 2.2uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C14 100pF 805 Capacitor Ceramic X7R Vitramon/VJ0805C15 10nF 805 Capacitor Ceramic X7R Vitramon/VJ0805C16 1nF, 250Vac 1808 Capacitor Ceramic X7R Syfer/1808JA250102KXBSY2C17 0.47uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C18 0.047uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C2 OPENC20 0.01uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C22 4.7uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C24 1uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C26 OPENC27 0.01uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C28 22uF Sanyo CV-FS Capacitor Electrolytic Sanyo/6CV22FSC29 10uF 1210 Capacitor Ceramic X7R TDK/C3225X7R1C106C3 150uF SANYO MV-WX Capacitor Electrolytic Sanyo/6MV150WXC4 1uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C5 1uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C6 680uF SANYO MV-WG Capacitor Electrolytic Sanyo/16MV680WGC7 1uF, 100V 1210 Capacitor Ceramic X7R TDK/C3225X7R2A105C8 1uF, 100V 1210 Capacitor Ceramic X7R TDK/C3225X7R2A105C9 0.01uF 805 Capacitor Ceramic X7R Vitramon/VJ0805D1 MMSD4148 SOD-123 Small Signal Diode Vishay/MMSD4148D3 MMSD4148 SOD-123 Small Signal Diode Vishay/MMSD4148D4 SMAJ_36V SMA Transient Suppressor Diode Diodes/SMAJ36D5 MURS110T3 SMB Surface mount schottky diode OnSemi/MURS110D6 MURS220T3 SMB Surface mount schottky diode OnSemi/MURS220D8 B130 SMA Surface mount schottky diode Diodes/B130-13D9 OPENL1 FERRITE BEAD Bead Core Ferrite Bead Core Panasonic/EXC-ML45A910HL4 47uH DO3316 Surface Mount Power Inductor Coilcraft/DO3316P-473MLL5 10uH 1812PS Surface Mount Power Inductor Coilcraft/1812PS-103KLQ1 MMBT3904 SOT23 N-NPN Bipolar Transistor Fairchild/MMBT3904Q2 SI4486EY SO-8 N-Channel Power MOSFET Vishay/SI4486EYR1 78.7k 805 1% Thick Film DALE CRCW0805R10 10k 805 1% Thick Film DALE CRCW0805R11 21.0k 805 1% Thick Film DALE CRCW0805R12 2.00k 805 1% Thick Film DALE CRCW0805R13 10 805 1% Thick Film DALE CRCW0805R14 0 805 1% Thick Film DALE CRCW0805R15 0.05, 0.1W 0805 1% Thick Film DALE CRCW0805R16 1.00k 805 1% Thick Film DALE CRCW0805R17 499 805 1% Thick Film DALE CRCW0805R18 499 805 1% Thick Film DALE CRCW0805R19 100 805 1% Thick Film DALE CRCW0805R2 10k 805 1% Thick Film DALE CRCW0805R20 10.0k 805 1% Thick Film DALE CRCW0805R22 10.0k 805 1% Thick Film DALE CRCW0805R23 86.6k 805 1% Thick Film DALE CRCW0805R25 30.1k 805 1% Thick Film DALE CRCW0805R27 OPEN 805 Page 1

bom2

FIGURE 2. Bill of materials, page 1

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NSC0607 LM5020/LP2992/LM2736 - Vin=9-42V,Flyback Converter: Vout =5V(I)@0.2A, 12V@2.1A w/ 5V@0.5A; and optional 3.3V@0.5A Buck Converter 12-13-2005

Designator Part Type Footprint Description ManufacturerR28 806 1206 1% Thick Film DALE CRCW1206R29 10k 805 1% Thick Film DALE CRCW0805R4 100k 805 1% Thick Film DALE CRCW0805R5 OPEN 805R6 OPEN 805R7 10 805 1% Thick Film DALE CRCW0805R8 2.49k 805 1% Thick Film DALE CRCW0805R9 10.7k 805 1% Thick Film DALE CRCW0805REF1 LMV431 SOT25 Low voltage precision shunt regulator National/LMV431REF2 LMV431 SOT25 Low voltage precision shunt regulator National/LMV431T10 EFD15-3F3-A63S EFD15 Power Transformer Coilcraft Custom/EFD15U1 LM5020-1 MSOP-10 100V Current Mode PWM Controller National/LM5020U2 PS2501-1-L PS2501 Surface Mount Opto-coupler NEC/PS2501L-1-HU4 LM2736-Y SOT23-6 Step-Down DC-DC Regulator National/LM2736U5 LP2992AIM5 SOT23-5 Micropower Low Noise LDO National/LP2992AIM5

BOM Total Considering Additional 3.3V Output C19 0.01uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C21 4.7uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C23 1uF 805 Capacitor Ceramic X7R Vitramon/VJ0805C25 OPEN 805R21 10.0k 805 1% Thick Film DALE CRCW0805R24 16.5k 805 1% Thick Film DALE CRCW0805R26 OPEN 805R3 100k 805 1% Thick Film DALE CRCW0805D2 MMSD4148 SOD-123 Small Signal Diode Vishay/MMSD4148D7 B130 SMA Surface mount schottky diode Diodes/B130-13L3 47uH DO3316 Surface Mount Power Inductor Coilcraft/DO3316P-473MLL2 10uH 1812PS Surface Mount Power Inductor Coilcraft/1812PS-103KLU3 LM2736-Y SOT23-6 Step-Down DC-DC Regulator National/LM2736

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FIGURE 3. Bill of materials, page 2

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5.0 Other Operating Values

Operating Values

Description Parameter Value Unit

Modulation Frequency Frequency 300 KHz

Total output power Pout 30 W

Peak to peak ripple voltage, 9Vin with full load Vout p-p 250 mV

Peak to peak ripple voltage, 42Vin with full load Vout p-p 200 mV

Dynamic Load Regulation, Vin = 9V, half load on 3.3V, 5V, Outputs, full load step Dynamic Load 400 mV

Dynamic Load Regulation, Vin = 42V, half load on 3.3V, 5V, Outputs, full load step Dynamic Load 300 mV

6.0 Layouts

layout9

FIGURE 4. Top Layer

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LM

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layout10

FIGURE 5. Middle Layer 1

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layout11

FIGURE 6. Middle Layer 2

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layout12

FIGURE 7. Bottom Layer

7.0 Waveforms

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waveform4

FIGURE 8. Output Ripple, Vin=42V

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waveform5

FIGURE 9. Output Ripple, Vin=9V

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waveform6

FIGURE 10. Load Transient, Vin=42V

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waveform7

FIGURE 11. Load Transient, Vin=9V

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waveform

FIGURE 12. Start up waveforms, Vin=42V

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waveform8

FIGURE 13. Start up waveforms, Vin=9V

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waveform9

FIGURE 14. Switching waveforms, Vin=42V

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waveform10

FIGURE 15. Switching waveforms, Vin=9V

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8.0 Physical Dimensions inches (millimeters) unless otherwise noted

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Notes

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Notes

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