Hi,
I'm having some trouble with a TPS54240 which is being used to generate a -ve 5V5 voltage rail of a 12V Vin. The circuit does work fine but I am finding that in some power up scenarios the converter will not regulate correctly and it takes excess current. The design is based on the SLVA317 app note.
What I am finding is that if I cycle the power to the circuit I can, quite repeatedly get the circuit to fail to power up correctly and I only get a ~-1V output and a significant increase in current draw. Oddly I only get this behavior if I physically pull the connector to my PCB out, I do not get this issue if I use the on/off from my bench top PSU to cycle the power, hence I feel its something to do with the transient response of the converter. There also appears to be a dependence on the timing between applying the power cycle, if I leave it between 2-5 seconds when the circuit is at room temp it repeatedly fails but if I leave it for greater than 8 seconds, it never fails? This timing also appears to have a dependence on temperature.
I have tried tweaking the Vin capacitance and the Cpole capacitor and these also seem to impact the timing of where the fault occurs but I have yet to be able to remedy the problem. It also appears that only some of my PCBs exhibit this behavior hence making it even more tricky to find a solution.
Any advice would be gratefully received.
Thanks,
Chris
