Hi Team, Here is the scenario, questions are, would the chip be damaged by the short because they want to remove the short and carry on with the qualification testing ( other wise they would have to start again) and can you explain why the fault showed up low temp testing?
We have had a controller sent back here with a failure from our customer.
After debug I discovered that it was the TPS24720 circuit that was failing. We are using this to create a “safe 5V rail” from a 5V rail with voltage and current monitoring.
But don’t worry its not a TI problem as I found that manufacturing had shorted pins 2 and 3 together.
The problem is whatever about quality missing it our testing didn’t catch it.
The issue is that at room temperature everything powered up ok and the circuit works away fine. We test the controllers during ESS at +65oC and -40oC before we ship them and this particular controller passed too.
This particular controller was going through qualification by our customer at the moment when the fault was found; EMC, humidity, temperature, etc.
However at low temperature -15oC or lower our customer discovered a failure where at power up software flagged a safe 5V rail fault as it was under 4.5V and a power good fault from the TPS24720. We can get it here too once we got it back.
Now maybe something has degraded overtime (from when it left here for qualification testing) to cause this fault to appear now at lower temperatures as we can’t understand how it passed at -40oC before it left here given we can get it so easily now.
It looks to me that the TPS24720 is in power limit mode during power up where the output is held to ~3.5V even though we have a 4.99k resistor on the PROG pin to eliminate a power limit. It actually comes out of it after 10 – 20 seconds and recovers.
I designed this circuit a number of years ago so I am trying to refresh myself on the device but my question to you is what are the consequences of shorting pins 2 and 3 together?
The timer pin sources and sinks 10uA of current to charge and discharge a certain capacitor to 1.35V. The PROG pin should not have any voltage on it? Is this the problem?
Why does it decide to go power limit mode a low temperatures?
Why is everything ok at room temperature?
Should we change the IC could it be damaged even though all functionality seems to be working ok since I removed the short?
Any advice or clarity you can bring to this would be great.
