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LP8764-Q1: Voltage at GPIO4 input

Bala Mahadeva iyer
Prodigy 190 points
Part Number: LP8764-Q1

We have a LP8764-Q1 based design. The GPIO4 is used as an enable input and there is no pull up selected for this input.

VCCA,PVIN_B1,PVIN_B2,PVIB_B3,PVIN_B4 = 5.0V

VIO = 3,.3V

We read VOUT_LDO = 1.8V

The actual design has 100K pullup on GPIO4. So instead of reading 3.3V @ the GPIO4, the node was reading 2.2V

I removed the 100K pull up resistor to 3.3V and we still do read 2.2V @ GPIO4. 

This was a working board and this board has gone through temperature stress test.

The part is working intermittently. When the board is subjected to vibration via tapping the board, the PMIC turns off output 

Trying to understand what could be going on. Should we remove this part and send it for failure analysis ?

  • 0
    TI__Expert 6440 points

    Hi Bala,

    Per datasheet if the pulldown is enabled it should be 400kohm typically. Meaning that with 100kohm pullup voltage should on range of ~2.64V.

    The symptom that part works intermittently is interesting. and tapping causes some behavior change. 

    Could you confirm if the device GPIO4-pin has pulldown enabled or not?

    And as first analysis i think A-B-A swap would be needed to confirm symptoms follows device not the board. 

    Br, Jari

  • 0 in reply to Jari Niemela13
    Prodigy 190 points

    Hello Jari

    As per the configuration file, GPIO4_PU_PD_EN  is disabled.

    As I mentioned, even when I remove the external 100K PU is removed from the board, I do read 2.2V on the GPIO4 pin

    Thanks

    Bala

  • 0 in reply to Bala Mahadeva iyer
    Prodigy 190 points

    Hello Jari

    In the GPIO4 config GUI there are two entries. The entries are as follows.

    a) GPIO4_PU_SEL. For this option, the selection in our config file is PullDown Resistor Selected

    b) GPIO4_PU_PD_EN. For this option, the selection in our config file is Disabled, Pull-up/Pull-Down Resistor

    On another board, having the same configuration file, when the 100K external PU is removed, I do see 0V at GPIO4 pin. But on the suspect board, I do read 2.2V even when the external 100K PU is removed. I will replace with another device

    Thanks

  • 0 in reply to Bala Mahadeva iyer
    Prodigy 190 points

    One correction... On the suspect board also, I do read 0V when the external 100K Pull up is removed.  I do not know why with Pull down disabled in configuration and with 100K PU to 3.3V, I do see 2.2V @ GPIO4 pin. Is there any errata in the configuration setup ?

  • 0 in reply to Bala Mahadeva iyer
    TI__Expert 6440 points

    Hi Bala,

    When pulldown is disabled there shouldn't be any path to gnd. Or it should very high impedance. So having 2.2V when 100kohm pullup is in place there is something not working right.

    Is there possibility for high voltage spike to that particular GPIO4 pin? What happens to pin voltage if you set pulldown enabled?

    There is no errata related to that pin. 

    Br, Jari

  • 0 in reply to Jari Niemela13
    Prodigy 190 points

    Hello Jari

    I tested the board with two configurations. Register 0x34 = 0x20 and register 0x34 = 0x24. In both situation, with a 100K external PU to 3.3V rail, the GPIO4 pin is reading 2.2V.

    To me, looks like you have an internal pull down enabled by default and the register 0x34 may be controlling only a Pull up scenario.

    May be you can try these configurations in your eval board.

    Thanks

    Bala

  • 0 in reply to Bala Mahadeva iyer
    TI__Expert 6440 points

    Hi Bala,

    In the register 0x34 bit 3 is the one controlling GPIO4_PU_PD_EN. So should data for the register be either 0x20 or 0x28?

    I measured on EVM. Both cases 0 V but with 0x20 setting resistance to ground is infinite and with setting 0x28 380 kohm. So my results are as I expected.

    Br, Jari

  • 0 in reply to Jari Niemela13
    Prodigy 190 points

    Hello Jari

    How do you explain with Reg 0x34 = 0x20 and with external 100K PU to 3.3V, we are seeing 2.2V @ GPIO4 pin ? IF there is no internal Pull down (as you explain with this setting), the voltage at GPIO4 should be 3.3V, Is it not ?

    Can you run this experiment on your board ?

    Thanks

    Bala

     

  • 0 in reply to Bala Mahadeva iyer
    TI__Expert 6440 points

    Hi Bala,

    This is interesting. With 100kohm external pullup, pulldown enabled, I get 2.178 V, close to 2.2 V like you, and without pulldown i get 3.03 V.

    This reminds me that there was discussion in the past that if the external pullup is too high pin can leak extra current and thus not settling to exactly expected voltage. Anyway even with 100 kohm external pullup voltage is still high enough to enable device. 

    So are you still seeing issues on starting device up?

    Br, Jari