LTC2924 , FAULT and On pin waveform

can you share the schematic as well?

Hi Sir 

As below , for you reference 

Hi Jason,

Thanks for sharing the schematic.

This looks like a power DOWN sequence as ON pin went from high to low and not a power up sequence as you mentioned in your first post. Can you confirm that.

The 5V used to power NE555, is it coming from one of the supply sequenced by LTC2924? If so, which supply is it?

Hi sir 

The VCC of the 555 circuit is the additional voltage

the waveform not to power down , This is what happened during the customer test.

Customer testing condition for output voltage , 0.65V/0.875V / 3.3V / 1.8V / 1.6V / 0.95VOUT

Does the customer's design circuit have any issue? 

Could  you please give me advice?

Hi Jason,

1. Can you elaborate the test that customer is doing?

2. Why does the ON pin goes low? This pin is connected to the EN pin of the NE555. Is NE555 pulling this pin low? 

3. Since ON pin is going low, this has to be a power down sequence test. In that case, please refer to fig#3 on the page#9 of the datasheet. It shows you the power down sequence profile of the part.

As you can see, Out4 will have to pass 0.61V (going down) threshold before starting the timer which will start the power down on Out3. It has to cross the 0.61V (going down) threshold before starting the timer which will start the power down on Out2 and so on. Can you check the scope shots of OUt4, Out3, Out2 and Out 1 to confirm that they are power down properly. Since I can see a FAULT signal at second charge discharge cycle of the TMR voltage, makes me think that either Out3 is not getting power down properly or 5V supply is glitching. You might also want to check if there are any caps on these OUTx pins which are not letting VOUTx pass 0.61V threshold.

Hi sir 

Updated as below:

Can you elaborate the test that customer is doing?

Why does the ON pin goes low? This pin is connected to the EN pin of the NE555. Is NE555 pulling this pin low? 

Ans : The output is 0.65Vout, the test state is in the Vin power on state, let 0.65Vout run 10~15 minutes, /FAULT Pin will drop down, this is the customer's unsolvable situation.

/FAULT is automatically generated drop-down situation, in this 10~15 minute interval test

Since ON pin is going low, this has to be a power down sequence test. In that case, please refer to fig#3 on the page#9 of the datasheet. It shows you the power down sequence profile of the part.

Ans : The spec P9 fig#3 you provided refers to the on pin timing states.
when I pull down on the pin. But the on pin is not pulled down during the test.

The fourth item you suggested, this we have verified and testing , know 0.61V threshold.

Thank you for your reply, and please confirm if there is a similar situation.