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BQ40Z50-R1 remaining capacity does not change at [PRES] = 0

Sake
Prodigy 160 points
Other Parts Discussed in Thread: BQ40Z50-R1

Dear all,



I'm developing 2s1p 1,500mAh Li-ion battery pack using BQ40Z50-R1 with 1-LED display.

LED is designed to light on 30% of the SOC.

To evaluate function of the LED, I adjusted the battery to 30% of the SOC with several charge and discharge. 

  note;battery voltage around 7.2V

Then LED lighted on correctly.

After that,  I left the battery for long term at the state of [PRES] = 0.

After two week, I checked the battery LED but it was still light on though it may less than 30% of SOC.

  note;battery voltage around 7.18V, current consumption is around 2mAh/day

Then,  I tried to change the state of [PRES] = from 0 to 1. After that, LED is no longer light on.

To know value of the SOC, I confirmed the battery with bqstudio. As a result, certainly the SOC was 28%.

So I think remaining capacity can't update correctly at the state of [PRES] = 0.

How can I solve it?

  • 0
    TI__Mastermind 34775 points

    Hello,

    Set DA Configuration[NR] = 1 to ignore PRES input. See bq40z50-R1 TRM for more details.

    5.2.1.1 System Present

    PRES is sampled four times per second, and if PRES is high for 4 samples (one second), the OperationStatus[PRES] flag is cleared. If PRES is low for 4 samples (one second), the OperationStatus [PRES] flag is set, indicating the system is present (the battery is inserted). If the [NR] bit is set, the PRES input is ignored and can be left floating.

    5.2.1.2 Battery Pack Removed

    The bq40z50-R1 detects the BATTERY PACK REMOVED mode if the [NR] bit is set to 0 AND the PRES input is high ([PRES] = 0). On entry to the BATTERY PACK REMOVED mode, the [TCA] and [TDA] flags are set, ChargingCurrent() and ChargingVoltage() are set to 0, the CHG and DSG FETs are turned off, and the Precharge FET is turned off (if used). Polling of the PRES pin continues at a rate of once every 1 s. The bq40z50-R1 exits the BATTERY PACK REMOVED state if the [NR] flag is set to 0 AND the PRES input is low ([PRES] = 1). When this occurs, the [TCA] and [TDA] flags are reset.

  • 0
    TI__Mastermind 34775 points

    Hello,

    The gauge is most likely going into sleep mode where it's keep track of the SOC, but not updating the SBS registers. When the gauge is awaken by the PRES = 1, it updated and the LED turned off.

    Essentially the gauge the needs to wake up to update the SBS registers and can be done by current or SMBus communication. If these are not feasible options, we can provide FW that allows this updating during sleep.

  • 0 in reply to Damian Lewis
    Prodigy 160 points
    Hello Damian,

    Thank you for your reply.
    Our customer's usage, there are possibility to leave the battery for long term without communication and load.
    And, this battery also need to reduce current consumption and turn off FET when this battery be left because this battery has additional DCDC circuit.
    So it's simple solution to use system present function [NR] =0.
    After long term left, customer need to confirm accurate SOC before connecting system([PRESS]=0).

    If possible, please provide new FW that allows SOC update during sleep or another solution.

    Thank you and best regards
  • 0 in reply to Damian Lewis
    Prodigy 160 points
    Hell Damian,

    I still need new FW that allows SOC update during sleep.
    Is it possible?
    If you need any more information from me, please ask me.

    Thank you and best regards