Tool/software:
Hello--
I recently created a prototype design using a TPS628438 buck configured for 1.8V output (see schematic and layout attached). Upon first application of ~3.6V to the input with the pushbutton held down, ~30% of units failed to have the 1.8V rail power up, and the remainder were fully functional. In this faulty condition, the EN pin rises to ~3.48V, the input current rises to ~300uA, and the regulator output voltage rises ~0.15V. The 500kOhm internal EN pull-down is active. There's a known issue with the size of the inductor footprint in this revision being slightly undersized, but even after attempted rework of the misbehaving units the behavior is identical. My questions are the following:
- Is this sort of behavior I'm describing consistent with what you'd expect if the regulator were powered on without a proper inductor connection to either of the SW or VOS pins?
- Would you expect the regulator to be irrevocably damaged after powering up with these steady-state conditions?
- Do you have any other leads for what this TPS628438 behavior might indicate or suggestions to root-cause the issue? I've included an x-ray sample below for reference, and I intend to send the faulty units back to the manufacturer for additional x-rays with improved contrast.
Note: If possible, I'd prefer that this post be made private. Thanks!
