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bq27520EVM evaulation board drawing 1-2mA off battery. Unable to relax battery.

Christopher Casebeer
Prodigy 160 points

I am having the issue that the EVM I am using is drawing 1-2mA off the battery when connected.

I know this as after having voltage droop, I used a TI A/D to sample a sense resistor with the battery. 

The only connections I can see which could be doing this is the BAT input pin of the bq27520.

I am not powering the battery monitor off the battery itself. However when I do, I am able to isolate the current which is used when I do power the battery monitor from the battery itself. Thus the 1-2mA current draw is not from the REGIN of the battery monitor. 

The issue is that I cannot relax the battery when I have this 1-2mA draw. Overnight this will take 100's of mV off my small 550mAh battery.

The input impudence of the BAT pin is too high for this current. Did I damage the BAT pin ADC?

Thoughts? Suggestions? 

Thanks in advance! :)

  • 0
    TI__Expert 4130 points

    Hi Christopher,

    Offhand I don't see a reason for you seeing that much current.  While the device is measuring BAT, it does have a 100kOhm internal divider that is switched in, but that should not draw anywhere near the current level you are seeing.  Is anything else connected to the cell (such as the I2C pullup resistors)?

    My colleague who is the expert on this device is out of this office right now, but I'll see if he has further ideas (other than a damaged board).

    Thanks,

    Terry

  • 0 in reply to -Terry
    TI__Expert 4130 points

    Hi Christopher,

    I can pass on some quick information from my colleague - he believed you probably aren't powering the chip using the battery based on your explanation. He suspects the means with which you are powering the chip is likely the culprit. One can’t power the chip from a different source and then use the gauge to measure the battery voltage, so it is a possibility you have damaged the chip.

    My colleague will be back in the office later this week and can help further.

    Thanks,

    Terry

  • 0 in reply to -Terry
    Prodigy 160 points

    Hi Terry,

    I wanted to reiterate that I am using an evaluation module which has a bq27520 on it.
    Here it is:
    www.ti.com/.../bq27520evm

    The evaluation module has a PACK+ and a EXT power supply path to supply REGIN. I had been using the EXT pin powered off the HDQ (VCC) of an EV2300. Both EXT and BAT+ both have the same problem.

    I did flash the G4 firmware to the board. I hope this didn't cause it my issue.

    I greatly appreciate the feedback on this issue. I've been persistently trying to generate a golden image for a while now.

    Things are better now though, as at least I have a chemistry match. 

  • 0 in reply to Christopher Casebeer
    TI__Guru* 76230 points
    hi Chris,
    You are probably doing something wrong somewhere because no way the chip can pull that much current if it isn't damaged. The current draw of the chip is sub 200uA when operating in normal mode.
    Do you have your set up connected as per the user guide of the EVM. Can you place a multimeter in series with the pack+ pin to measure the actual current pulled by the chip.
    Also, power the chip off vbat and not the external supply. If you are still getting the same problem, try replacing the IC to see if the issue goes away.

    thanks
    Onyx