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bq25101h !CHRG LED won't turn off

roy stevens
Prodigy 70 points
Other Parts Discussed in Thread: BQ25101H, BQ25101

Hello, I am using the Bq25101H to charge at a max rate of 36mA. Everything works as it should except the !CHRG pin doesn't go low when the battery current drops below 10% in the voltage regulation and charge termination phase.  We observed the charging current go from 36mA down to 1mA, and the !CHRG remains low. 

Notes: 

1) We are using an internal pullup on a processor pin to pull !CHRG high during high impedance state.

2) The datasheet mentions that for charge rates below 50mA, an RC filter should be used across the ISET resistor. We tried with this filter and the issue is still there. 

Thanks, 

  • 0
    TI__Genius 14890 points

    Roy,

    I have verified your results in the lab.  I noticed that after VIN is applied, the first termination is at 1mA.  Successive recharge terminations occur at 3.6mA as expected.  I am meeting with the design engineer to investigate further.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 70 points

    Hi Dick, Any info on this? We're all waiting with bated breath.

  • 0 in reply to roy stevens
    TI__Genius 14890 points

    The bq2510x family has a default termination current of 1mA.  The bq25101H overrides this and sets the limit to 10%. Based on the results I have seen, this override feature is not enabled properly on the first taper of 10%, instead the 1mA limit is used.  If VIN is not removed, any recharge taper current is properly set to 10%.

    In your original post, you noted you went down to 1mA and CHG remained active (low). Can you verify that it does terminate below 1mA. 

    I am working with the designer on other devices in this family to fully understand the nature of the 1mA termination instead of 10%.  

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    TI__Genius 14890 points

    Roy,

    The bq25101 is working properly.  The error in my analysis is that I did not take into account the CHG pin LED current.  The source meter I used to emulate the battery shows how much is going out of the EVM, not out of the OUT pin.  Since the LED is tied to OUT and GND, its current is not taken into account.

    In my initial post, you'll recall I noticed a difference in termination current between the first termination and the recharge termination.  The bq25101 disables the LED during recharge cycles.  In this case, the definition of recharge is the battery decreases enough to create a recharge, but VIN remains in place.  If VIN is cycled, then the LED would turn on.

    The EVM uses a few mA for the CHG LED.  What is your LED current?  This should explain why the device does not terminate. 

    Float CHG to verify the correct termination current.

    Design simulations verify these results.

    Regards,

    Dick