Hello.
We have product powered partly with TPS40400. There is voltage sequence, where each voltage level is followed with each other always, when previous stage returns PW_GOOD signal. How ever there is some problems with 1V0_AVS voltage, since it seems that TRACK pin has somehow defected on some of units.
There is voltage monitoring device, which releases TRACK-pin voltage voltage to 3,3 V when previous voltage VCC has exceeded 3,09 V.
See picture:
With units working normally there can be seen behaviour like picture on top. There is short transient and then voltage quite rapidly stabilises to 1 V.
Units which are not working correctly, behaviour can be seen at bottom. There is approx. 4V output from TRACK pin with short bursts approx. 1,6 kHz frequency, during phase when voltage monitor tries to keep pin down. After voltage monitor releases TRACK pin to 3,3 V voltage output stabilizes to approx. 4,2 V.
Behaviour has been verified to be causes TPS40400 by removing all other components from TRACK pin. There is still approx. 4 V output, but voltage monitor does not try to pull line down.
