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TPS3890: Reset Delay Time

Allan Fan
Expert 7780 points

Part Number: TPS3890

Hi expert,

Customer used TPS389033 and used 0.01uF C(CT) which hope to have 10ms delay time. 

However, we didn't see the 10ms delay time happened. Could you please help advise what might goes wrong?

p.s. the time division is 5ms. 

Regards,

Allan

  • 0
    TI__Genius 12920 points

    Hi Allan, 

    Thank you for your question!  The schematic seems correct to me. Can you please provide the following clarification to better assist you?

    -What is your measured delay? 

    -What kind if capacitor are you using for C594 (CT pin)?  Since according to datasheet, in order to minimize the difference between the calculated RESET delay time and the actual RESET delay time, it recommends using a low-leakage type capacitor (such as a ceramic capacitor) and minimize parasitic board capacitance around this pin.

    Best Regards,

    Sila Atalar

  • 0 in reply to Sila Atalar
    TI__Expert 7780 points

    Hi Sila,

    The time interval is 5ms so it seems almost no delay. 

    Customer used X7R MLCC

    Customer need is to have 10ms tPD(falling) time but the formula we see in the DS seems is tPD(rising) time.  

    Can the tPD(falling) time be configurable? What's the formula to get tPD(f) in terms of CT?

    By the way, the formula for tPD(r) in pin description and Equation1 seems not match.  The value 1.07 in pin description seems not right cause Vct(min)*Ict(max) is not 1.07 and should be 0.0000016. Please correct me if any misunderstanding. 

    Regards,

    Allan

  • 0 in reply to Allan Fan
    TI__Genius 12920 points

    Hi Allan, 

     You can obtain 1.07 value by using the equation in below. In the datasheet Vct(min) is defined as 1.22V and the current is 1.15uA. The micro are going to cancel each other. The value for 1.07 is provided for a faster calculation.

    I checked with my team and I don't think you can configure this device for tpd(f). For this case TPS3899 can be a better option, since it has CTS pin and by connecting 10 uF at CTS pin you can get 6.2 second sense delay. 

    Please let your customer know about this device, and I hope this helps. 

    Best Regards,

    Sila Atalar