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BQ25792: Still "fast charge" set after finishing charging battery

Herbert S
Prodigy 50 points
Part Number: BQ25792

Dear Supportteam

After finishing charging, the status (0x1c) is still on "Fast Charge" .

Battery current is 0mA.

Load is powered from Input Source.

I thought, the charge Timer (0x0e set for 12h) is waiting this time (in this case 12h) before starting charging again.

After charging and before starting again, the Status should be "not charging" - right?

kind regards

Herbert

  • 0
    TI__Mastermind 35155 points

    Hello,

    I am a little confused by your setup. The charge voltage is 7.3 V, the ADC battery voltage is 6.631 V, and it is done charging? Can you please measure the battery voltage and see if it agrees with the ADC? If your battery is at 6.631 V you definitely would still be in the CC region. How big is the load when this is happening?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi Mike

    The velues seems right. This is an 2S2P LiFePo4 Pack. Datasheet tells me to use 7300mV for charging. The package voltage is 6,4V nominal.

    There is a small diference. In BQ Studio VBAT = 6906mV. On the Battery clamp = 6741mV.  On Bat_charger+ = 6804mV (See schematic below)

    The Shunt generates  a voltage drop of 10mV. 

    This is a endurance test with connected  12V/4A powersupply.

    In the meantime the device starts charging again. The ADC for the charging current is total wrong (see question #4779604).

    The load is a tracking unti with 80-120mA and works with an voltage range from 5-24V.

    kind regards

    Herbert

  • 0 in reply to Herbert S
    TI__Mastermind 35155 points

    Hello,

    I am still confused by your statements. If the charge voltage is 7.3 V, the battery should not be fully charged at 6.4 V.

    What do you mean by "Battery Clamp?" What is the pin BAT voltage on the device?

    BQ25792 can only support 3.3 A input current.

    Can you please explain your load setup more clearly? What is the SYS voltage, what is the SYS current, what is the BAT voltage, and what is the BAT current at this time?

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi Mike

    The OCV voltage of te battery-pack is 6.4V.

    Acccording to the data sheet I set the charging voltago to 7.3V.

    Voltage on the battery connector is  6741mV

    Maximum charging current is 800mA, so 1A input current is enough - no need to the full 3.3A.

    The status (Register 0x1c) is on "fast charging" but there is no battery-current. 

    The main question is why the status is still on "fast charge" with no current flowing into the battery.

    The status should be "not charging".

    kind regards

    Hebrert

  • 0 in reply to Herbert S
    TI__Mastermind 35155 points

    Hello Herbert,

    There is something not right about the understanding. If the charging voltage is set to 7.3 V, it is fully charged at 7.3 V not 6.4 V.

    Please measure the battery voltage, system voltage, system current, input voltage, input current at this observation. Capture all of the registers again. Record the SW node waveform when there is no charging.

    Also, it looks like termination is disabled, try enabling termination.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 50 points

    Hi Michael

    Set 0x0F<<1 to 1  (enable termination) 

    When the charging voltage is reached in the quick charge or taper charge process, the charging process is no longer stopped without comment. Now I get the message "DONE" and the load is fed from the input source, if available.

    The next test: When is the charging process restarted if there is an uninterrupted supply.

    kind regards

    Herbert