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TPS65921B power up problem

Jason Senior
Prodigy 50 points

We are using the TPS65921B companion chip to power an AM3707 device.

We have 4 identical PCBs, 2 operate correctly and 2 are exhibiting similar faults.

Both of the boards are configured in master mode configuration.

Board one has no DC-DC voltage outputs other than 1.8V. There is no 32kHz clock present and VRTC is 0V. SysEn and Warmreset are being pulled low by the device. PwrOn is high (3.3V). SysEn=0.5V. HFCLK out = 0.5V.

Board two has DC-DC 1.8V present and the other 2 supplies attempt to come on and then power off again.  There is a large periodic pulse every 200ms which coincides with the supplies trying to power up. The 32KHz clock is present (0.5VP-P with 0.7V dc level). SysEn and Warmreset are being pulled low by the device. PwrOn is high (3.3V). SysEn=0V! HFCLK out = 0V.

If the 3.3V input supply is lower to 3V and the device powered up the spike is not present.

Thankyou

  • 0
    TI__Expert 6090 points

    can you please check if there is any kind of short on the board, from what you are explainaning it seems like there is a short and device shuts down because short circuit triggers.

    You can try to remove the laod and see if the board boots up properly.

  • 0 in reply to Puneet Sehgal
    Prodigy 50 points

    Hello

    Thanks for the response. Yes we have checked for potential short circuits and have compared resistances with a working board. One of our thoughts is whether we have a device population problem and the output sense lines may be open circuit. I will keep you posted.