TLV171: output pull high issue

Hi Jimmy,

please remove the caps "PC701" and "PC72". They are counterproductive in the positive (hysteresis) feedback loop, as they slow down the traverse through the threshold region. But the sense of the positive feedback is just to speed up the traverse. So you kick the gas pedal and the brake pedal at the same time...

If you need supply voltage filtering, split PR258 into two resistors, a big and a small with the small hanging at the supply voltage and the small being way smaller than the big. Wire a low pass filtering cap from the midpoint of these two resistors to signal ground.

Kai

Hello Jimmy,

With the power supply at zero, the op amp is not powered so it can't control the output. An external signal pulls output high which activates internal diodes in the op amp that should not pass any significant current.  Because the peak is over 2V, the external current into output pin is far too large.

Hi Ron,

We appreciated your great support!

Customer's issue as below, could you guide us how to resolve it?

Many Thanks,

Jimmy

Jimmy,

When power is on, the op amp should control PFC_C node. What powers this node when op amp is off? This circuitry should be reviewed.

Hi Jimmy,

have you thought about adding a transistor stage to the output, similar to this thread?

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1074090/lm2903b-output-status-under-vcc-2v-during-power-up

Kai