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TPS3808: TPS3808G30DBVR Reset delay time not meet our design

Godfrey Chen
Prodigy 60 points
Part Number: TPS3808

Hi Sir,

   I found TPS3808G30DBVR which delay time setting not meet our CT selection.

1. Our current CT value used 200nF on the U68, so the Reset delay time should be 1.143s.

But when I measured the waveform, I can see the 530ms and 1.3s delay time as below waveform.

Can you tell the root cause why the reset delay time not very accurate?

2. Does the TPS3808G30DBVR is sensitivity on cold temperature? When I used refrigerant to blow the TPS3808G30DBVR and CT capacitors, it seems like the reset delay time will drop to 130ms and 220ms. And this symptom is continued unit I remove the power and then powered on the device again. This symptom will recover after the removal power and then power on again, do you know what's the reason to cause this symptom? It seems like the reset delay IC not very stable.

CT:200nf  Reset delay time:1.3s

CT:200nf  Reset delay time:530ms

CT:200nf with refrigerant  Reset delay time:220ms

CT:200nf with refrigerant  Reset delay time:130ms

 

Thanks

Godfrey

  • 0
    TI__Mastermind 18690 points

    Hi Godfrey,

    The first thing I would suggest is to use lower tolerance capacitor like a X7R. This will minimize your timing variation and maximize stability. It is also an expected outcome for timing to vary across temperature. As for reference, the table below shows the expected timing variation if CT is connected to 180nF capacitor and test if tested across -40°C to 125°C.

    Jesse