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BQ21040: Device appears to be stuck in reset loop?

Ryan Walker
Prodigy 235 points
Part Number: BQ21040

Hello,

We are using the BQ21040 in a handheld device to charge a 710mAh battery via USB. Charge current is set to ~500mA with a 1K resistor on ISET. TS is connected to a 10K NTC thermistor in the battery pack. The USB charger is rated for 2A and we have confirmed that the input voltage on the BQ21040 is above 4.2V when charging at full load. For the most part, everything operates as expected.

However, some of our customers are experiencing a state where the battery appears to be mid range (not fully charged, not fully depleted), but the charge will not initiate. We are having difficulty replicating the state, but we were briefly able to reproduce and were able to snag a quick picture (attached) of the VIN behavior during this state. While we weren't able to capture the state on any other pins, I did briefly see that the VOUT was exhibiting a square wave that corresponded with that of the VIN between charging and not charging.

I have tried simulating many conditions to try and trigger the state but have been unsuccessful. Occasionally we are able to enter this state by repeatedly plugging and unplugging the charger on devices where we have seen this behavior. Since opening the device this state has been lost, and I have been unsuccessful in generating it again. We have seen this reported by several customers, and have seen it in the lab on at least 3 separate occasions and 3 separate devices.

Currently we have no way of "snapping" the device out of this state. Customers are left with a device that will not charge and it has to be returned. With the device opened, physically disconnecting the battery seems to reset this state, but this is not possible by the end user.

If anyone has any ideas for things to try/test to reproduce this state and determine the cause it would greatly appreciated!

Thanks,
Ryan

  • 0
    TI__Guru* 75606 points

    Hello Ryan

    This could be Battery Detect routine triggering.

    Charger will source and sink current during this time while looking at voltage.  Times on your scope capture looks similar.

    Additional resistance between the Out Pin and battery terminal will increase the chance of triggering battery detect.  Most often when near charge complete.

    See figure 9 of data sheet.

  • 0 in reply to Bill Johns
    Prodigy 235 points

    Hi Bill,

    After reviewing the Battery Detect flow chart think I now have a better idea how it operations.

    However, I haven't been able to simulate the behaviour by manually adding resistance between the Out Pin and the battery terminal. What I do see is that the battery is not detected, and charging never commences. I don't see the "square wave" behaviour of charging and stopping which leads me to believe this isn't the problem.

    Also, we see the behaviour more frequently at lower battery voltages (below 4V), and it seems to correlate higher with customers that discharge the battery voltage until it's completely dead. However, charging from the "dead" state (typically 3V, and worst case 2.4V) seems to work fine. A subsequent charge after this state seems to present the issue more often.

    When stuck in this state, by mixing and matching charge cables/power supplies we can get the device to sometimes charge. It doesn't seem to correlate with the quality or capacity of the cables or supplies. We have a set of known good cables and power supplies, including a captive cable design that can guarantee 5V at the end terminal, with a 2A capability. Even with this setup the device will not charge.

    The USB data lines in our design are not used, and are left floating. Not sure if is this could contribute in some way?

    Looking for anything else to try to get this resolved.

    Thanks,
    Ryan

  • 0 in reply to Ryan Walker
    TI__Guru* 75606 points

    A couple of things to check.

    1.) When you seen the sq wave what is the max and min voltage?

    2.) If you can check the ISET pin voltage, this represents current out?

    3.) Double check the time should be about 30mS, scope capture shows about 30mS?

  • 0 in reply to Bill Johns
    TI__Guru* 75606 points

    Hello

    Any update on this problem?

  • 0 in reply to Bill Johns
    Prodigy 235 points

    Hi Bill,

    Sorry for the delay. We're having trouble reproducing the problem in the lab. We're getting a few devices sent back from a client that were exhibiting this problem, so hopefully we will have something we can test with in the next few weeks.

    Thanks,
    Ryan