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BQ24725A: No Charging possible and BATDRV always 0V

Part Number: BQ24725A

Hello,

Sadly no charging of the battery (3S1P with 3Ah) is possible (ACOK is high).

Also the BATDRV Output is always 0V (Even if the AC Adapter is not present).

I am using as AC Adapter a lab PSU (24V Current Limit @ 2A)

When iam using your Evalboard everything is working fine.

The system load is only a tiny 3.3v StepDown Regulator for the MCU.

I have attached the schematic and a part of the layout.

With friendly regards

Mark RudolphBS2000-M4-PSU-039_SCH.PDF

  • Hi Mark,

    I don't see any obvious errors in your schematic. Can you please provide the following information to help debug this further?

    1) What are your register settings?

    2) Can you capture a waveform showing VCC, ACOK, PHASE, and REGN during adapter plug-in, similar to Figure 1 in the BQ24725A datasheet? Also, what is the battery voltage during this test?

    3) Can you capture another waveform showing VBAT, VSYS, BATDRV, and REGN when only the battery and the system are connected?

    4) "+11V_System" is the input to your 3.3 V regulator, correct? With a traditional topology charger like the BQ24725A, the system rail can go as high as the adapter voltage (24 V) or as low as the battery voltage.

    Best regards,

    Angelo

  • Hello Angelo,

    1. The register settings are:

    ChargeVoltageLimit = 12592 mV

    ChargeCurrentLimit = 1000 mA

    InputCurrentLimit = 2000 mA

    _ChargerOptions.bits.Charge_Inhibit = 0u; //Default 0
    _ChargerOptions.bits.ACOC_ThresholdAdj = 0u; //Default 1
    _ChargerOptions.bits.NotInUse = 0u; //Unused
    _ChargerOptions.bits.AC_AdapterInication = 0u; //Read Only
    _ChargerOptions.bits.I_OutSelection = 1u; //Default 0
    _ChargerOptions.bits.LearnEnable = 0u; //Default 0
    _ChargerOptions.bits.I_FaultLowSideAdj = 1u; //Default 0
    _ChargerOptions.bits.I_FaultHiSideAdj = 0u; //Default 1
    _ChargerOptions.bits.EMI_FreqAdjEnable = 1u; //Default 0
    _ChargerOptions.bits.EMI_FreqAdj = 0u; //Default 0
    _ChargerOptions.bits.BAT_DepletionAdj = 3u; //Default 3
    _ChargerOptions.bits.WatchdogTimerAdj = 0u; //Default 3
    _ChargerOptions.bits.ACOK_DeglitchTime = 1u; //Default 1

    but i tryed varies other parameters too.

    The "Charge_Inhibit " was set/reset at runtime without any changes.

    The communication via I2C is Ok, i can readout my set parameters from the IC.

    2. Screenshots Picture 1.png 

    3. Screenshots Picture 2.png 

    4. Thanks for the comment, the system voltage can vary between 7V to 28V.

  • Hi Mark,

    Thanks for the additional information. However, why would VSYS go up to 28 V if your adapter is 24 V?

    Let's try a simple test as a sanity check for the BATDRV issue. Disconnect everything from your board - the adapter, the system load, the battery, and the host MCU. Now, apply a voltage from BAT to GND using either a power supply or a real battery. BATDRV should rise to SRN + 6 V, thus turning the BATFET on and allowing the battery to power the VSYS rail. If even this test doesn't work, then it's possible that your BQ24725A IC is damaged.

    When I try this on an EVM and apply 12 V to BAT, then BATDRV rises to 18 V to turn on the BATFET, and VSYS = 12 V, as expected.

    Best regards,

    Angelo

  • Hi Angelo,

    The System Voltage will never be 28V, but the Design is able to handle it.

    To the sanity Check.

    I have disconnected the AC Adapter and the load.

    The MCU was erased.

    The Battery Voltage is 12V from a PSU

    The current Consuption is approx. 1mA

    The BATDRV Voltage is 11.7V

    The Voltage at the SRN Pin is 12V

    The VSYS  is 11.63V

    The REGN  Voltage is 0.02V

    The IC was replaced.

    With friendly regards

    Mark Rudolph

  • Hi Angelo, 

    I have found the problem with the BATFET, the connection to the SRN Pin was broken.

    So the BATFET is now working fine. (The gate voltage is 17V with a 11V Battery).

    Now i have the Problem with charging the Battery.

    The IC tries to charge the battery for a short time (less 1msec), and then stops it (ACFET turns off, and BATFET turns on again)

    I have attached 3 screenshots

    Complete

     Detail

    At the end

    With friendly regards

    Mark Rudolph

  • Sorry i forgot my MCU Settings:


    Charge_Inhibit = 0
    ACOC_ThresholdAdj = 0
    I_OutSelection = 0
    LearnEnable = 0
    I_FaultLowSideAdj = 1
    I_FaultHiSideAdj = 0
    EMI_FreqAdjEnable = 1
    EMI_FreqAdj = 0
    BAT_DepletionAdj = 0
    WatchdogTimerAdj = 0
    ACOK_DeglitchTime = 0

    Charge Voltage is 12,592V

    Charge Current = 512mA

    Input Current Limit is 4A

  • Hi Mark,

    Thanks for the update regarding the BATFET! I'm glad that's working now.

    Section 8.4.5 in the datasheet lists the conditions needed to enable or disable charging. Your waveforms and register settings rule out most of these possibilities, but can you please verify ILIM, ACDRV, SRN, and the short circuit conditions?

    • Charge is enabled: yes

    • ILIM pin voltage: ?
    • All three DACs programmed with a valid value: yes
    • ACOK valid: yes
    • ACFET and RBFET turn on and gate voltage is high enough: ?
    • SRN < BATOVP: ?
    • IC temperature < TSHUT: I'm assuming this isn't an issue because the IC only tries to charge the battery for <1 ms before the converter stops switching.
    • Not in ACOC: No, your register settings disable ACOC.
    • Short circuit is detected: ?
    • Watchdog timer expired: No, your register settings disable the watchdog timer.

    Best regards,

    Angelo