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TPS23756: 24W Application

Victoria Qin
Intellectual 1250 points
Part Number: TPS23756

Hi,

Customer is using TPS23756 for their system, there are some bugs which occurred in 2 out of prototypes.

About these 2 abnormal prototypes, the system worked normally at first one year, then when the POE VDD to VSS and adaptor still works normally but VB/VC to COM doesn't have voltage and there is no GATE signal output. 

The schematic is as below. Is there any problem in circuit design which could cause this problem?

Thanks.

Victoria

  • 0
    TI__Mastermind 19151 points

    Hi Victoria,

    Thanks for reaching out to us!

    VC - COM is the voltage source to regulate VB and provide the +bias of the gate voltage. So I would suspect it could be the root cause.

    There are two paths to source VC: 

    #1. The integrated current source to charge the VC. It ends when startup ends.

    #2. External circuit to charge the VC by the auxiliary winding 4-5. 

    I would recommend you to check the #2 issue first: 

    1. check the R168 and D14 to see if it is broken due to overheat. What are the package for them? 

    2. What is the capacitance of C63 and C95

    3. Could you use the scope to extract the waveform of VC-COM? That will be very helpful for us to look for the cause.

    Also, could you send a pdf version of a picture with higher resolution? I could not see the components parameters clearly. Thanks.

    Best regards,

    Diang

     

  • 0 in reply to Diang Xing
    TI__Intellectual 1250 points

    Hi Diang,

    I would like to update this thread and further communication by email, because this case is probably related with IC failure. 

    Thanks.

    Victoria

  • 0 in reply to Victoria Qin
    TI__Mastermind 19151 points

    Hi Victoria,

    Thanks for connecting me in email. I will reply by email and close this thread for now.

    Best regards,

    Diang