TPS92630-Q1: TPS92630-Q1 Fault pin works abnormally during transient test

Hi Dorson,

i want to confirm some points about this case:

1) in the schematic i see the fault pin connect to the fault_s pin do you externally pull them high with a resistor(the R value and the voltage rail you pull up) or just leave them floating? do you connect them to mcu?

2)what't the Vf and if of the LED string?

3)about your describtion",the fault pin of some samples will recover to high level and work normally, but the fault pin of some samples couldn’t recover and keep low level." i want to know whether the sample which couldn’t recover can work normally in your case(the led can lit up)?

4)how many tps92630-q1 you are use in the system

Hi Frank 

Many thanks.

 1) I didn't pull them hign with resistor .,just connect with  2PCS TPS92638's fault pin .like as below shotscreen.

    Is that I need to pull up the fault pin with resistor in application ?I remember there is an internal pull-up  in the chip .Right ?

2, Vf of the LED ,typical voltage bin we select  is 2.15V~2.6V

3)some of the fault pin couldn't recover ,and LEDs are unlit .There is no output current .

4)There are left and right circuit  in the system ,they are symmetrical .What I showed to you is the lesf circuit .2 TPS92630-Q1 in system .4 TPS92638-Q is system.

 I also found another abnormal phenomenon  ,EVEN all the fault is pulldown to low level .Some channels of TPS92638-Q1 could still have output ,some of LEDs still keep lit.   It didn;t meet the 'one fail all faill 'requirement .It's odd.

Pls help me fix this problem .thanks Frank.

Or could you tell me how to verify that it is because of the inadquate  power supply ? I adjut the value of input 3 caps which I marked ,it seems to work normally ,but I am not very sure .

Hi Frank 

      One more detail,After I disconnect the fault pin between TPS92630-Q1 and 2PCS TPS92638-Q1 ,During the transient test ,2PCS TPS92638Q1 could work normally ,even not enlarge the input capacitor ,but the fault pin of TPS92630Q1 will be pull down to low level ,but Fault_S keeps high level all the time .Only enlarge the bypass capacitor could fix the problem .I have no idea why the feature of Fault pin is associated with the input capacitor . 

That's why I ask for help about TPS92630Q1's application .

Could you help me to capture the wave form of Vin iout(TP17) FAULT and ref pin's voltage waveform when you use 1uF and 10uF input cap with the scale of 500us/div and 1s/di.

i want to confirm the differences between two conditions.