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BQ25895M: Battery voltage read is 0 when not charging even though the battery is not depleted yet.

Tung Nguyen51
Prodigy 170 points
Part Number: BQ25895M
Other Parts Discussed in Thread: EV2400

Hi,

I have set the battery chip to host mode and ADC conversion type to continuous 1s.

I have checked that I got ACK from the bq25895M as well. 

I can read battery voltage using my C++ program when the battery is charging, but I receive 0 as soon as I stop charging the battery. 

I don't understand why and how to fix this problem. Do I need to set anything else?

Any helps would be appreciated. 

Thanks. 

  • 0
    TI__Intellectual 1910 points

    What is the expected battery voltage?

    There is a limitation that BAT voltage needs to be about SYS_MIN setup.

  • 0 in reply to SamW2000
    Prodigy 170 points

    Hi, 

    Thanks for your answer. 

    The BAT should be about 4.1V which is greater than SYS_MIN which is 3.5V. When I stop charging, BAT goes back to the default value which is 2.304 V.  

    I have made sure that the following conditions are satisfied: 

    1. BAT > OTG_BAT_EN

    2. VBUS < BAT + VSLEEP

    3. OTG_CONFIG bit = 1

    4. B_HOT and B_COLD bits are within range 

    5. Wait 30s. 

    Is there anything else that I need to do?

  • 0 in reply to Tung Nguyen51
    TI__Mastermind 46611 points
    Could you please provide all the register values? Thanks!
  • 0 in reply to Ning T
    Prodigy 170 points

    Hi Ning,

    Sorry for the late reply. This is all the register values. 

    Thanks. 

  • 0 in reply to Tung Nguyen51
    TI__Mastermind 46611 points

    The register values provided do not show BAT ADC reads 2.304V. Based on the register values, REG0E[6:0](i.e.BAT)=45(HEX), i.e. 3.684V, REG0F[6:0](i.e.SYS)=45(HEX), i.e. 3.684V and charge state REG0B[4:3]=00 (i.e. not charging). These readings look normal. I have translated the register values to HEX values. You may plug in the attached register txt file into the bq2589x GUI by "load Registers" and confirm the BAT ADC readout. Thanks!

    BQ25895M Battery voltage read is 0 GUI.txt 
    * Created: Thu Jul 19 23:58:39 CDT 2018
*
* Format: Register Name  tab Character,\t  Hexadecimal register value.
* BQZ Container: Charger_1_00-bq25895M.bqz
*
Input Current Limit, HIZ and ILIM pin	00
OTG Temperature thresholds, and Input Voltage DPM Offset	05
ADC controls, OTG Frequency, ICO, DCP, and Input Detection	70
Battery Load, WDT Reset periods, OTG and Charge Enable, and MINSYS setting	3A
Fast Charge Current Limit settings and MTK Pump enable	20
Pre-charge and Termination Current Limit settings	13
Charge Voltage Regulation Limit, Battery Low Voltage and Recharge threshold	82
Termination Current Enable, STAT pin, WDT, Safety Timer, and JEITA Charge Current	8D
IR Compensation and Thermal Regulation thresholds	03
ICO, Extended Safety Timer, BATFET control, MTK Pump Voltage, and JEITA Charge Voltage	44
OTG Regulation Voltage and Current Limit settings	93
Charger VBUS, Charging Mode, PG, USB Input, and System Voltage Regulation status	02
WDT, OTG/VBUS OVP, Thermal Shutdown, Safety Timer, and TS pin faults	00
Input Voltage DPM settings	54
Thermal Regulation Charge Status, and ADC Battery Voltage conversion	45
ADC System Voltage conversion	45
ADC TS pin voltage as percentage of REGN conversion	3F
VBUS status, and ADC VBUS Voltage conversion	00
ADC Charge Current conversion	00
DPM status, and Input Current Limit setting	2E
Registers reset, Input Current Optimizer status, Device ID, and Temperature Profile	3A

  • 0 in reply to Ning T
    Prodigy 170 points
    Hi Ning,

    Thanks for the answer.

    I have tested and confirmed that VBAT value when not charging is correct. It is not the case with charging.

    When the battery is charging, the VBAT does not reflect the true voltage of the battery. Particularly, when charging the VBAT can read 4.1V, and VBAT right away be 2.304V when unplugging from the charger. Moreover, the VBAT can go above the maximum voltage that it has which is 4.2V.

    I can read the VBAT correctly when charging if I use EV2300 and bq25895MEVM_664. I just can't read it correctly when debugging using bq25895M board.

    Is there any settings that I need to set for bq25895M to read the VBAT correctly when charging? Such as a setting to stop charging when reading the voltage.

    Thanks.
  • 0 in reply to Tung Nguyen51
    TI__Mastermind 46611 points

    We have to duplicate the behavior your mentioned in order to understand and resolve it. Could you please try to duplicate the behavior on the bq25895M EVM with EV2300 or EV2400 and let us know the detailed test procedure to duplicate the behavior you described? Thanks!

  • 0 in reply to Ning T
    TI__Mastermind 46611 points
    We haven't heard back from you for a while. The thread is considered closed. Thanks!