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Original question:

BQ25895: Strange behaviour of my BQ25895

BQ25895: BQ25895 charge complete interrupts

Mike Snyder
Intellectual 285 points
Part Number: BQ25895

Hi! 

I notice when my battery reaches 150-200mV towards the chargeTerminationVoltage, I get interrupts every ~40 ms with no faults (fault reg reads 0). 
I assume this is telling me the charge is complete, however my unloaded battery voltage is still short of the target. 
I've tried raising the Charge Voltage Limit but I'm still getting constant interrupts

> bq
temp: 24.080139
vbus: 5.100000
vbat: 4.104000
ichg: 0.000000
vbus stat: 5
ichg stat: 0
vsys stat: 0
temp rank: 0
chg fault: 0
getMinVbus: 4.700000
getBatLoad: 0
getChargeEnable: 0
FastChargeCurrentLimit: 0.960000
InputCurrentLimit: 0.400000
PreChargeCurrentLimit: 0.128000
TerminationCurrentLimit: 0.256000
ChargeVoltageLimit: 4.208000

Reviewing interrupt sources, process of elimination says charge complete - 
• USB/adapter source identified (through PSEL or DPDM detection, with OTG pin)
• Good input source detected
– VBUS above battery (not in sleep)
– VBUS below VACOV threshold
– VBUS above VVBUSMIN (typical 3.8 V) when IBADSRC (typical 30 mA) current is applied (not a poor source)
• Input removed
• Charge Complete
• Any FAULT event in REG0C

 

  • 0
    Intellectual 285 points

    Follow up - 
    Changing ChargeVoltageLimit to 4.3 v didn't help
    Changing ChargeVoltageLimit to 4.4v shows it charging again. 

    I think I'm just seeing the active charge voltage telling me to shut the thing down before the actual battery voltage (not charging) hits the threshold. 

    Is it common place to add 100 mV or so to the target voltage while charging?

    esp> bq
    temp: 22.910065
    vbus: 5.000000
    vbat: 4.404000
    ichg: 0.300000
    vbus stat: 5
    ichg stat: 2
    vsys stat: 0
    temp rank: 0
    chg fault: 0
    getMinVbus: 4.900000
    getBatLoad: 0
    getChargeEnable: 1
    FastChargeCurrentLimit: 0.960000
    InputCurrentLimit: 0.400000
    PreChargeCurrentLimit: 0.128000
    TerminationCurrentLimit: 0.256000
    ChargeVoltageLimit: 4.400000

    Not seeing any interrupts yet. Ichg is dropping as expected. 

  • 0 in reply to Mike Snyder
    TI__Mastermind 32010 points

    Hi Mike, 

    To confirm if the interrupts are related to charge terminating can you confirm if CHRG_STAT (REG0B bits 4:3) is changing between fast charging and charge termination statuses? 

    Referring to the first set of statuses you provided can you confirm if "ichg stat" maps to CHRG_STAT? I have some confusion because it also seems charge is not enabled (getchargeEnable: 0). 

    Mike Snyder said:
    before the actual battery voltage (not charging) hits the threshold

    This observation could also relate to voltage drop between the BAT pin and actual battery terminal on your PCB. The voltage drop will be present while there is charge current, but no longer observed when ICHG = 0A. Please keep in mind the BQ25895 can only measure the battery voltage at bat PIN, not the true battery terminal voltage.  

    Mike Snyder said:
    Is it common place to add 100 mV or so to the target voltage while charging?

    We have had some customers do this, but I recommend you check with your battery manufacturer to understand the potential side effects of charging the battery to a higher voltage. 

    Best Regards,

    Garrett