WEBENCH® Tools/LM5122: Output shorted - Abnormal behavior

Fernando Rigon

Prodigy 20 points

Part Number: LM5122
Other Parts Discussed in Thread: LM5121

Tool/software: WEBENCH® Design Tools

Hi;

I set up a boost converter as recommended by the Webench using the LM5122 out 24V @ 5A;

After testing, I noticed abnormal behavior. The source supply can start with output shorted to gnd;

Also if the converter is switching input and you close the short to gnd, the converter will not turn off both mosfets.

Does anyone know if I can turn off both mosfets? Have you had the same problem?

Tks

over 6 years ago

0 Youhao Xi over 6 years ago

TI__Guru* 78070 points

Hi Fernando,

Thank you for using the LM5122 in you design. Sorry I am confused by your descriptions. What do you mean by close the short to gnd? What do you mean by not turn off both mosfets? Can you show the MOSFET gate drive signal? HO to SW, and LO to GND, in the same scope picture with Vout and Vin?

As you may know, boost converter does not have a natural mechanism to protect against output short, because even if the two FETs are not switched, the body diode of the high side FETwill give the current the path from the input to the shorted output. If you want to protect against output short, please consider the LM5121

Thanks,

Youhao Xi

0 Fernando Rigon over 6 years ago in reply to Youhao Xi

Prodigy 20 points

Thanks Youhao Xi, you helped me a lot;

Now i saw, the LM5121 have a full output protection.

LM5122 describe in your datasheet only "hiccup-Mode Overload Protection" and the LM5121 " Hiccup Mode Short Circuit/Overload Protection"

LM5122 not turn off boths mosfets in short circuit;

I can't understand how I didn't see this difference before starting my project;

Again, thanks Youhao Xi;

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WEBENCH® Tools/LM5122: Output shorted - Abnormal behavior