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TPS40055: Please review the schematic, and have a question.

Chase Jeong
Mastermind 7365 points
Part Number: TPS40055
Other Parts Discussed in Thread: TPS40057

Hello TI experts,

My customer now check the schematic of TPS40055. Could you review the schematic first?

and they have a problem that sometimes the output is not detected even input power is applied.

they do not use PR57 resistor, so COMP(pin8) is floating.

is it necessary to connect COMP pin to operate TPS40055? what happens if COMP pin is floating?

I attach waveforms of startup.

: Upper line is SS pin. yellow is fault operation and white is normal operation.

Lower line is 5V output. sky-blue is fault operation and white is normal operation.

: This is the current consumption when the fault is detected in startup.

Please check this issue. Thanks.

Best regards,

Chase

  • 0
    TI__Guru 58171 points

    Hello Chase 

    The functionality of the device has been verified with proper compensation components at the COMP pin. It is not guaranteed that the device works as expected if you don't use proper compensation components. 

    I guess it is current limited, but as I mentioned it is not guaranteed that the device works as expected if proper compensation components are not used

    -EL  

  • 0 in reply to EricLee
    Mastermind 7365 points

    Dear EL,

    Thank you for your support.

    I discussed about this issue with my customer. Actually they use TPS40057 in another application.

    They did not see the same issue even pin8 of TPS40057 is floating. TPS40057 is working well.

    here is the question;

    1. what is the exact role(function?) of the resistor in front of COMP pin? do you have any document to refer?

    2. Is there any possibility of abnormal operation if we float COMP pin of TPS40057?

    (cause my customer did not see any abnormal operation in TPS40057 operation under same condition of TPS40055)

    Best regards,

    Chase

  • 0 in reply to Chase Jeong
    TI__Guru 58171 points

    Hello Chase 

    1.Please refer page17 in https://www.ti.com/seclit/ml/slup340/slup340.pdf for more information about type 2 compensation. Basically, the resistor creates a zero to compensate a load pole. 

    2.It is not recommended to leave COMP open. Since the functionality of the device has been verified with proper compensation components at the COMP pin. It is not guaranteed that the device works as expected if the COMP pin is floating.

    -EL