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UCD9248: UCD9248 Startup Problem

canberk unal
Prodigy 150 points
Part Number: UCD9248

Hi, 

I am using Xilinx's KC705 development board and there are three UCD9248 ICs on it. Most of the time when I power the board, these ICs don't startup. Therefore, board doesn't startup either. They designed the board(UCD9248 part) exactly what datasheet says. I think it is beacause of the reset pin. Because when I touch the reset pin, IC goes into reset state and hold until I touch next time. I uploaded the schematic of this part. How can I fix this problem. 

Thanks in advance. 

Canberk 

  • 0
    TI__Mastermind 24075 points

    HI Canberk 

    Can you use TI Fusion to check how ON_OFF_CONFIG is set on UCD9248?

    If ON_OFF_CONFIG is set as "control pin only", then PMBUS_CTRL pin (pin 36) must be high to turn on rails. 

    If ON_OFF_CONFIG is set as "option only", PMBus host must send an on command to UCD9248 to turn on rails. 

    If ON_OFF_CONFIG is set as "always converting", UCD9248 will turn on rails once 3.3V voltage is applied. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 150 points

    Unfortunately I don't have PMBUS cable, but I will get asap. 

    PMBUS connector on the board doesn't connect to any host. On the design they connect PMBUS control pin to UCD9248's 3V3 output with 2k pull-up resistor. I added the schematic of this part. I measure 0V  on the PMBus-control pin when it doesn't startup, and I measure 3V4 when it starts-up normally. 

  • 0 in reply to canberk unal
    TI__Mastermind 24075 points

    Hello, 

    Based on what you observed, the rails are controlled by PMBUS_CTRL pin voltage. 

    The PMBUS_CTRL pin voltage is determined by external circuit. 

    Sorry I'm not familiar with Xilinx's KC705 development board, you may need to contact Xilinx why PMBUS_CTRL pin voltage is low when the board is powered on. 

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 150 points

    Thank you very much for help, Qian, 

    PMBUS_CTRL pin isn't connected to anything other than UCD9248's 3V3 output(pull-up with 2k resistor). Is it possible that UCD9248 may make this pin 0V? Otherwise these IC's may be damaged. 

    Regards, 

    Canberk

  • 0 in reply to canberk unal
    TI__Mastermind 24075 points

    Hi Canberk,

    Can you check PWRCTL1_VCC3V3 voltage when PMBUS_CTRL pin voltage is low?

    Thanks

    Qian

  • 0 in reply to Qian Chen
    Prodigy 150 points

    Hi Qian, 

    I checked it when it happened, it was still 3V3. How touching reset pin solve this issue, I don't know. 

    I have ordered TI's USB -interface adopter to reprogramme chips, it if helps. 

    Regards, 

    Canberk