I have a circuit using LTC3350 that is showing odd behavior and wonder if anyone could help me resolve the issue?
When Vin is increased from 0V to 12V the capacitors do not start charging. This behavior is consistent across all boards. The prototype worked reliably, but maybe this was a fluke?
When probing the design to try to find the issue I have found that touching the PFI pin sometimes kicks the design into life and the capacitors then charge perfectly.
Looking at the SW node, as I gradually increase Vin from 0V to 12V the SW node starts switching when I reach ~5V (at 500KHz as expected). However when I get past 11V it suddenly stops and the charger sits there doing nothing (see images)
I've run out of things to try! I can't see anything wrong with the schematic, maybe I'm missing something?
The design intent is as follows:
1/ Vcap ~10V
2/ Switches over to back-up mode when Vin falls below ~9.9V
3/ Charge current limit set to 4A, but total current limited to 640mA (expectation is ~150mA load and 500mA left over for charging)
4/ Backup voltage is 12V
