Other Parts Discussed in Thread: TPS563208, TPS54202, TPS562219A, TPS562208
Hello,
Our application uses TPS561208 with input 12V and 5V output at 700mA load current – all nominal values. Our application also requires a very large cap (~2200uF) on the output to provide sufficient energy to finish some downstream work in case of power loss. We believe this large cap is causing startup problems as we see 16ms hiccup triggering at the output. Specifically,
1. When we have a 25 ohm resistive load (~200mA load current) at the output during power-on, we don’t see any startup issues. When we add another 25 ohm in parallel while the supply is up (i.e. increase load current dynamically to 400mA), we see output voltage is stable and things work fine.
2. However, when we have two 25 ohms resistors in parallel as resistive load (~400mA load current) at the output during power-on, output does not become stable and we see hiccups at the output with saw tooth waveform. When we remove one of the 25 ohm load resistors, the hiccup goes away and output becomes stable. When I add the 25 ohm resistor back in parallel, output remains stable.
We have not tried removing the large cap - we assume the startup issue will go away with it.
What are our options now?
- Reduce the large output cap from 2200uF or move the cap elsewhere.
- Try a different part – other than TPS561208. This option is as bad as the previous one for us.
- Any other options/suggestions?
Large caps are known to trigger overcurrent protection circuit in switching regulators during startup. What are the standard techniques folks adopt to address the issue?
Appreciate your help,
Satish Acharya
