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LM5009: Min. output voltage for LM5009 reboot

lu xiangdong
Prodigy 50 points
Part Number: LM5009

Dear TI expert,

Application ： 75Vin  --> LM5009 buck 14V  --> LDO TPS70933 3.3V

In order to save power consumption, the min. load of LM5009 only has LM5009 FB resistors (47K+10K) and LDO load (3~4mA).

For this application, it is no problem for first time power on if Vout of LM5009 is 0.

The problem shows below,

Step1: Vin switches on and waits 5s

Step2: Vin switches off and wait 1~2s

Step3: Vin switches on again

The result is that LM5009 can't reboot due to the output of LM5009 is higher than 2.5V, as shown in picture below.

Only wait the output of LM5009 is dropped to < 2V, LM5009 can reboot again.

Is there a min. output voltage for LM5009 reboot ? or is there some other root-cause cause this issue？

Hope to get your feedback ASAP.

Thanks in advance.

Xiangdong.