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TPS40422: CH2 output failure

JH Shin
Mastermind 9815 points
Part Number: TPS40422

Hello,

My customer has a problem that the output of the TPS40422 CH2 below does not operate normally during production.

TPS40422_SCH_2022.11.30_2.pdf

When they replaced  the TPS40422 with another or changed the C22 capacitor value from 470nF to 1uF, the output worked fine.

1. Are there any other roles of C22 Capacitor besides the current sensing contents of the datasheet?

2. How to calculate the proper value for C22 capacitor?

3. Is it okay to use 1uF for the C22 capacitor value in the circuit above?

Thank you.

JH

  • 0
    TI__Mastermind 27330 points

    Hello,

    The time constant with C22 = 470nF is enough. I think the noise is coming from the switching node and increasing the clamp circuit may solve the issue. You can use 1uF. please check this paragraph.

    Regards

  • 0 in reply to Mahmoud Harmouch
    Mastermind 9815 points

    Hi Mahmoud,

    Thank you for your reply.
    The customer has further inquries.

    1. Does the power inductor's inductance value have anything to do with the switching node noise you mentioned?
        Unlike the inductor value shown in the above schematic, the actual assembled inductor is a 0.68uH product. (PN:PG0077.801NL)



    2. What is the role of resistor R20? (Resistor R16 based on EVM circuit)
       Is it okay for the user to use this resistor?

    Regards,

    JH

  • +1 in reply to JH Shin
    TI__Mastermind 27330 points

    Hello,

    1- if the inductor series resistance DRC is higher, the sense voltage is higher as well. Changing the inductor can also increase the switching noise because the noise is related to layout and component placement.

    2- R16 forms a voltage divider with R6 (referring to TI EVM). R16 can be added to lower the sense voltage on CS2P pin

    3- R20 is in the snubber circuit. The lower the R20 the lower the noise on switch node.

    Please close the thread as resolved if your questions are answered and let me know for further support.

    Regards