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BQ40Z60 no longer turns on

Austin Hendrix
Prodigy 125 points
Other Parts Discussed in Thread: BQ40Z60, BQ40Z50-R1, BQ24725A

Up until about a week ago, my custom PCB with a BQ40Z60 had been working well, with no trouble. I had disconnected the battery from the board several times for a short period of time, with no trouble.

About 1 week ago, I disconnected the battery and the charge cable so that I could put my development system away and work on other projects.

Now, when I plug in either the battery, the charge cable, or both, my board does not turn on. I'm not able to communicate with the BQ40Z60 over SMBus using the EV2300 dongle, and both the PBI and Regn pins measure 0V.

I'm using the BQ40Z60 in a 4S configuration, based closely on the "Typical Application" in the datasheet.

  • 0
    Prodigy 125 points
    After reading this post: e2e.ti.com/.../489382 , I measured the voltage drop across the ACP resistor. My supply voltage is set to 19V, but the voltage on the ACP pin is only 15V. This suggests that 0.4mA is flowing through the ACP resistor.

    This is consistent with a 37.5k pull-down, which is within the 30-50k pull down range listed on the datasheet for the ACP pin.
  • 0 in reply to Austin Hendrix
    TI__Guru 73830 points
    Austin
    The 40 kohm pull-down resistor is only active when the gauge is trying to enter shutdown. I do not see a drop on the ACFET, but I do see a drop across the 10 kohm series resistor in the ACP signal path. This drop is due to the ACFET charge pump.
    Tom
  • 0 in reply to ThomasCosby
    Prodigy 125 points
    I do not see a voltage on the gate of my ACFET, and I see a small drop across it. I suspect the drop is due to the body diode in the FET, since the FET is off.

    The bigger question here is why the BQ40Z60 isn't active, even though both battery and AC power are applied.
  • 0 in reply to Austin Hendrix
    TI__Guru 73830 points

    If you have voltage on ACP and VCC, then the device should be active. It must be damaged.

  • 0 in reply to ThomasCosby
    Prodigy 125 points

    Ok. I did a risk build of two boards, and the BQ40Z60 has failed on both boards in different ways. I think it's time to change the design.

    Can you recommend a different part or set of parts that provide charging, balancing and gauging for a 4-cell lithium-polymer battery, and would support user-replaceable batteries?

    I'm willing to sacrifice some gauging accuracy, I'm willing to limit the charging current, and I'm willing to limit the minimum and maximum cell voltages if it means I can use off-the-shelf batteries that are commonly used by hobbyists.

  • 0 in reply to Austin Hendrix
    TI__Guru 73830 points
    If you want to use a smart charger, then I would recommend using the bq40z50-R1 gauge with the bq24725a charger. The bq40z50-R1 is a higher performance gauge/protector/balancer than the bq40z60. But, these gauges were not optimized to support "host side" applications where the user replaces the cells. They learn the state of the cells and have to relearn the state of the new cell when it is attached. It may take several cycles for the gauge to learn the new cell. A CEDV type gauge may be a better option for this type of application. We have several CEDV gauges released and some newer ones in the pipeline.