Hi experts:
My customer is designing an open loop, isolated, push-pull DC/DC with LM5030. The circuit seems working properly while there are some issues in output short circuit test. The input current during output short circuit is high. To reduce the short circuit input current, engineer change soft start cap from 0.1uF to 1uF however no any effect, the input current is same. Engineer observed the SS pin voltage during output short (see below picture). Strangely it seems the SC protection is properly triggered while the SS cap is not fully discharged in both condition (0.1uF and 1uF Css). Css voltage is discharged down to 0.8V and recharge again. Such device is not disabled at all. I think this is the reason why the input current is not reduced when change Css from 0.1uF to 1uF. I have two questions about this issue:
1) Why Css is not fully discharged?
2) Does the Sort-Start function work properly in this open loop application? considering the Soft start function controls start up process through error amplifier, while in open loop application the error amplifier is in fact disabled (FB is grounded)
Thank you!
John
