I am working on a board that has three TPS61196PWPR LED drivers ICs per board. Two of the drivers seem to intermittently come up.
Attached is a schematic for the LED driver.
When the driver does not start, we narrowed it down to the VREF voltage never ramping up after the unused detection pulse. We never make it to the point where the buck converter turns on (never saw a single pulse on the gate of Q2). Attached are a couple pictures of an event when the driver started and another of when the driver did not start.
The LEDs are on a different board where we terminate each LED string (17 of them) with a 10M to ground, Each string is composed 16 LEDs in series for two of the LED drivers. The other LED driver has 20 LEDs in series per string. The voltage drop across each LED is 3V.
Here is a section of the LED board schematic:
Again, the problem seems to be related to VREF never ramping up as it is supposed to do.
Thanks for your help,
Waveforms for a time when the driver started okay and when the driver did not start:
