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BQ25792: STAT pin is always Hi-Z

Jeff LaBundy
Intellectual 300 points
Part Number: BQ25792

Hi there—our platform connects the STAT pin of the BQ25792 to a high-impedance input of another IC, which enables an internal weak pull-up to 1.8 V.

I find that the STAT pin is Hi-Z (pulled up to 1.8 V) for all values of the CHG_STAT register field, including 3'b011 (CC) and 3'b100 (CV). According to my understanding, the STAT pin should be Hi-Z only for 3'b111 (done). Here is a register dump during one such instance:

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00: 04 01 90 01 f4 2c 00 32 c3 08 23 00 dc 4b 3d a2
10: 80 40 00 01 16 aa c0 7a 55 00 32 8f 6a 01 00 00
20: 00 00 00 00 00 00 00 00 ff c7 7f 1f ff fc 80 00
30: 00 01 eb 01 a6 13 8e 13 86 13 88 0f 90 0f a9 02
40: 57 00 2a 00 00 00 00 00 08 ff ff ff ff ff ff ff

We can see that register 0x1c = 0x6a (CHG_STAT = 3'b011 = CC) and register 0x13 = 0x01 (DIS_STAT = 1'b0 = STAT pin enabled), yet the STAT pin is not driven to GND by the BQ25792. Are there any other conditions that can disable the STAT pin?

Thank you in advanced for your support and in case I can clarify any of my observations, please let me know.

  • 0
    TI__Mastermind 31761 points

    Hello Jeff,

    Have you tried using a different pull up rail, such as REGN, for testing purposes?

    Best Regards,

    Christian

  • 0 in reply to Christian Moyer
    Intellectual 300 points

    Hi Christian—thank you for your prompt support!

    I cut the trace between the STAT pin of the BQ25792 and our third-party IC, then pulled the STAT pin up to VBAT using a 47k external resistor. However, the result was the same—the STAT pin remains Hi-Z, even though charging is active.

    In case there is anything else you would like me to try, please let me know.

  • 0 in reply to Jeff LaBundy
    TI__Mastermind 31761 points

    Hello Jeff,

    Can you provide your schematic?

    Is this device charging normally?

    What is the input voltage/ current?

    What is the battery charge voltage/ charge current?

    Best Regards,

    Christian.

  • +1 in reply to Christian Moyer
    Intellectual 300 points

    Hi Christian—thanks again for your steadfast support. The device charges normally; the only problem is that the STAT pin does not track the CHG_STAT register field.

    However, I think we can close this case as an assembly issue. I went back and checked this behavior on an older lot of PCBs, and the STAT pin functions as expected. With this latest lot, however, there is no continuity between the exposed contact of the QFN package and the test point I'm using.

    I wedged a narrow resistor lead onto the exposed contact of the QFN package and pulled it up to 1.8 V; the actual STAT pin tracks the CHG_STAT register field normally now.

    I loosely suspect we have some sort of SMT issue with pads along the corner of the device—we'll investigate internally. However, there is no longer any question about the device itself. Thanks again for your assistance, and apologies for the noise!