I just received my first 2 articles of a board which utilizes a TPS65910 with an AM3505, One of these boards behaves as expected, the 2nd board is exhibiting some strange behavior. In particular, the bandgap reference (VREF) is low (in the 700mV range versus 850mV as expected), but increases over time (minutes). At some point, the 3.3V on SW2 pops on near what I expect as does the 1.8V on SWIO (but low (1.5 - 1.7V). Generally, I have my 1.2V (SW1) at the expected voltage, but the other voltages are low (the various VAUXs) which seem to be tracking the bandgap reference. Additionally, these voltages and the behavior of the output overall, varies over time. If I leave it powered up, the 3.3V, the 1.8V (on SWIO) and even the 1.2V (on SW1) will drop out altogther. My input voltage is fine (5.0V).
My question is what would affect the bandgap voltage and cause it to be low? All I have connected is a 0.1uF cap to VREFGND/GND.
I've ordered a replacement part, but it's not clear if this is the likely culprit. Is it likely I have a faulty part, or should I look elsewhere?
Any thoughts or insights are greatly appreciated,
Thank you,
Kevin Taberski
