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Original question:

AMC7932

AMC7932 time sequence issue for power supply

Chi Zhang2
Expert 3030 points

Other Parts Discussed in Thread: AMC7932

Dear team

for AMC7932 application for RRU, we have a issue for power time sequence. the power supply include Vdd(5.2V), VIO(1.8V), Vcc(A,B)(8V)

in the datasheet, there is no limit for power time sequence. so we start Vdd first, then VIO and then Vcc.

but before Vcc turn on, the Vdd 5.2V will drop to 3.3V, and then back to 5.2V. the detail is shown as the attachment. if so any affect for the device function?

BR

Chi

  • 0
    TI__Guru 56933 points

    Hi Chi,

    I don't know of any specific issues that this will have.  If the other supplies are held low, then the device will stay in POR until VIO is allowed to rise.  

    In general, I would not recommend this sequencing.  Can the supply glitch be removed?

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    TI__Expert 3030 points

    Hi, Paul

    Thanks for your reply.

    because our datasheet didn't recommend a power time sequence, could you give us a reference to remove this glitch?  customer is afraid to try other unsuitable way.

    BR

    Chi

  • 0 in reply to Chi Zhang2
    TI__Guru 56933 points

    Hi Chi,

    It is difficult to make a recommendation to prevent the glitch without knowing the cause of the glitch.  I think this would be caused by the VIN of the LDO or SMPS that generates VDD is not consistent.  You could add large capacitors to the input of the DCDC converter, or you could use a voltage supervisor to disable the DCDC until it's input is valid.  

    Could the supply be collapsing at startup because it lacks current drive capability?

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    TI__Guru 56933 points

    Let's take this over email.