Hi,
I have a few protoypes that use a TPS54340 to switch 12V down to 3.3V. On one of my boards, I have run into an issue where after about an hour or so of run time, the enable pin on the regulator will unexpectedly and drop from 4.2V down to 0.5V. Once the voltage has dropped, it switches between roughly .5 and 1.5 at what seems to be random intervals.
In order to attempt to diagnose the problem, I purchased the EVM for the TPS54340 and ran the following test.
Boards 1 and 2 are the boards that are not showing any issues. Board 3 is the faulty board that has gone through multiple regulators
Boards 1 and 2 are populated as designed.
On board 3, the output cap, the inductor and R39 are removed. I connect the output of the EVM to the ground and 3.3V rails on board 3.
I power each board off of their own power supply set to 12V. I left the boards to run overnight and when I get back, they are all fine.
This tells me that the load side of the regulator is not the issue on any of these boards. Is this a valid conclusion?
Believing that the load side was not the problem, I replaced the regulator and the supporting passives pictured in the schematic with fresh components.
Unfortunately, it seems like the issue has not resolved itself, the original symptoms persist.
I have also tried a few other things:
- adding a resistor divider (32k and 10k) to the enable pin. On boards 1 and 2, this worked correctly, but on board 3 the enable pin voltage would eventually drop from around 3V to 0.7V.
- After having the enable pin voltage drop on Board 3, I added a 1k pull up to 12V. The enable pin voltage was also 12V. The regulator worked as desired, but I know that this is out of spec and I don't know what the long term implications are of running the part out of spec.
I'm starting to run out of ideas as to what could be wrong and I would appreciate any help that would me get a better understand of what is causing this problem.
I have attached the schematic and layout of the the regulator and supporting passives
Erick
