LM5118: VOUT and AGND short

Abhishek Vazrekar93

Part Number: LM5118

I have developed a buck-boost using the web bench.Attached it the schematic from web bench.Only thing I have changed is instead of one RFBT resistor, I have used two ( one 10K RFBT2 potentiometer and other 100ohms RFBT1) and RFBB 536. So basically I can vary my pot speed from 1.4v-24V.Everything works fine for few days rather months, then suddenly voltage drops to the lowest.And when we check the continuity VOUT and AGND are shorted.I have had 5 of such cases.final 2.7Amp Web bench design.pdf

over 7 years ago

0 Youhao Xi over 7 years ago

TI__Guru* 78060 points

It is little confusing: your RFBT=10K+100 =10.1k, and RFBB=536, while the webench recommended RFBT=18.7k and RFBB=1k. Why do you change these values away from the Webench recommended, but not adjust the loop compensation in accordance?

What to you mean by 1.4V to 24V?

Can you show us some waveforms of the switch nodes, Vout ripples, and a step load response.

0 Abhishek Vazrekar93 over 7 years ago in reply to Youhao Xi

Intellectual 555 points

Youhao Xi said:

What to you mean by 1.4V to 24V?

I want to vary the output voltage from 1.4-24 volt to drive a dc motor using potentiometer.

0 Youhao Xi over 7 years ago in reply to Abhishek Vazrekar93

TI__Guru* 78060 points

So, to adjust Vout, I would recommend you to stay with the Webench recommended circuit, and change the low side resistor namely RFBB. This will keep the circuit stable for different Vout settings.

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LM5118: VOUT and AGND short