Tool/software:
We have identified a critical issue in production units that are already distributed in the field. This situation is extremely urgent, and we require immediate support.
Our setup: Main supply --> Noise filter --> eFuse --> DCDC --> ICs
Problem Description:
- When a very low-level noise is present, the DCDC regulator output drops to ~1V for <100 ms, causing the entire system to shut down and restart.
- The issue occurs even at minimal load conditions.
- The behavior is independent of the supply range (10VDC to 28VDC).
- We have narrowed the problem to the FLT pin asserting the wrong signal.
Noise Correlation:
- The noise at the main supply input is already properly filtered before reaching the eFuse. This means that in theory, the TPS26622 input doesnt see the noise in theory.
- However, the output voltage drop of our DCDC always coincides with the presence of this noise at the main input.
- To reproduce the problem, we connect another PCB to the same power source as the affected PCB—this consistently triggers the restart.
For some reason we have a note saying that a pullup resistor wasnt needed between Fault pin and SS/INH pin from the DCDC but the fact is that what we are experiencing is fixed by a pullup. Right now it is impossible to add a pull up resistor due to the compact assembly and cost of the rework process.
The option we considered following the datasheet is to leave the FLT pin floating, so we just need to cut a track and isolate the pin. The problem is that in this case the eFuse is not supplying any output if FLT is left floating; we are forced to connect the FLT pin to RTN (second option adviced in the datasheet). Can you please recommend anything else?
Thanks
