WEBENCH® Tools/LM5122: Unstable operation

Anton Kocherov

Part Number: LM5122

Tool/software: WEBENCH® Design Tools

Hello, i try to start up DC-DC convertor based on LM5122. Input is 12V, output is 24V/8A/ Frequency - 750 kHz. Covertor drops down load at 4.5 Ohm (or 5.3A output current). Converter is tryed to start on load higer than 4.5 Ohm but not sucsessful. What problem may be here? Schematic file is attached.

Firstly I tryed simulate my design by WeBench Power Design Tool, but this tool isn't support my design paramets. I dont know why. How I can simulate my design?

LM5122 DC-DC.PDF

over 5 years ago

0 Youhao Xi over 5 years ago

TI__Guru* 78220 points

Hi Anton,

Thank you for using the LM5122. While I am forwarding this to our responsible engineer, could you show some waveforms like the LO, COMP, and SW when the circuit does not regulate the output voltage?

Thanks,

Youhao Xi, Applications Engineering

0 Anton Kocherov over 5 years ago in reply to Youhao Xi

Prodigy 210 points

Hello, I made some waveforms as you said (all voltage are respected to the ground). Load is 4.5 Ohm.

1. Load drop process (output voltage)

2. LO and SW Signals togeher

3. COMP signal and LO

0 Richard Fu22 over 5 years ago in reply to Anton Kocherov

TI__Mastermind 31125 points

Hi Anton,

Sorry to hear you are having troubles.

Your schematic looks ok, but your switch node looks wrong in that the peak should be the switch node plus a diode drop. Can you check the VT1 FET and make sure you have connected it properly and make sure there is no damage?

Thanks,

Richard

0 Anton Kocherov over 5 years ago in reply to Richard Fu22

Prodigy 210 points

Great thanks, power supply was started. I resolder VT1 and all became ok. May be it was small metal pieces.

0 Anton Kocherov over 5 years ago in reply to Anton Kocherov

Prodigy 210 points

I'm sorry. LO and HO are signal togehter on this picture (HO -top, LO- bottom).

0 Richard Fu22 over 5 years ago in reply to Anton Kocherov

TI__Mastermind 31125 points

Hi Anton,

Let's close this thread here, and continue on the other thread you posted here: https://e2e.ti.com/support/power-management/f/196/t/886771

Thanks,

Richard

Power management

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WEBENCH® Tools/LM5122: Unstable operation