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Original question:

BQ25792: VSYS Falling Low after a few seconds

BQ25792: IBAT 0mA while fast charging

Michael Potas
Prodigy 30 points

Part Number: BQ25792

Tool/software:

Hi, I'm having some issues with battery charging using the BQ25792.
Specifically the battery does not appear to charge and 0mA are going to or from the battery when I read register REG33_IBAT_ADC, when the charger is reporting that it is in fast charge mode, without faults.
Its a 2 cell battery.
The charging supply is 12V and limited to 300mA.
VBUS reads 12V, VSYS and VBAT read 7V, which agree with voltmeter measures.
IBUS reads 17mA.

An LTC2959 fuel gauge is also being used to monitor current to and from the battery, and it reports a constant discharge current, even while the BQ25792 it is in fast charge mode.

My team mates and I are failing to understand why its not charging and what the cause of the problem is.
Please let me know what further information my team mates and I can provide to assist with the solution.

Thank you.

  • 0
    TI__Mastermind 20620 points

    Hi Michael,

    Thanks for posting. Monday is a US holiday.  A team member will get back to you later this week. Thanks for your understanding.

  • 0 in reply to Jing Zou
    TI__Intellectual 1110 points

    Hi Michael,

    Do you have a large SYS load? If the device is in supplement and supplying charge from the battery to SYS then it will not appear on the ADC in forward mode.

    Regards,

    Jared Baxter

  • 0 in reply to Jared Baxter
    Prodigy 30 points

    Hi Jared, thanks for your reply.

    There is a bit over 30mA being drawn from the battery. I have been able to read this from the BQ IBAT_ADC while in discharge mode.
    It remains about 30mA discharge even when the BQ enters fast charging. 
    The BQ is reporting 17mA on IBUS with 12V VBUS, and I am supplying 12V limited to 1A. 
    Oddly the power supply shows 0mA being drawn, though the BQ is reporting 17mA.

    Is it correct that if the power draw of the load is greater than the power provided by the charging then it won't charge the battery?
    Would any of the default firmware configurations (or faults) prevent IBUS from drawing the maximum available current (up to the limit based on PROG)?

    Thanks

  • 0 in reply to Michael Potas
    TI__Intellectual 1110 points

    Hi Michael,

    Can I get a register dump of the issue occurring, including ADC values?

    To answer your other questions:

    Michael Potas said:
    Is it correct that if the power draw of the load is greater than the power provided by the charging then it won't charge the battery?

    Yes, this is supplement mode. The datasheet overviews this in section "8.3.8.2 Dynamic Power Management".

    https://www.ti.com/product/BQ25792#tech-docs

    Michael Potas said:
    Would any of the default firmware configurations (or faults) prevent IBUS from drawing the maximum available current (up to the limit based on PROG)?

    The ILIM_HIZ pin sets a high clamp on IINDPM unless EN_EXTILIM=0. 

    Regards,

    Jared Baxter

  • 0 in reply to Jared Baxter
    Prodigy 30 points

    Hi Jared

    This is all the registers a few seconds after CE has been pulled low. Supplying 12V, with 2A limit.
    I see 0mA drawn from the PSU (charger)

    Reg: 0, value: 0x12 0b10010 //VSYS min 18 * 250mV + 2500mV = 7000mV
Reg: 1, value: 0x3 0b11
Reg: 2, value: 0x48 0b1001000 //Charge_Voltage_Limit Register 840 * 10mV = 8.4V 2 cells
Reg: 3, value: 0x1 0b1
Reg: 4, value: 0x2C 0b101100 //Charge_Current_Limit Register200 *10mA
Reg: 5, value: 0x6B 0b1101011 //Input_Voltage_Limit Register 107 * 100mV = 10.7V
Reg: 6, value: 0x1 0b1
Reg: 7, value: 0x2C 0b101100 //Input_Current_Limit Register 300 * 10mA = 3A
Reg: 8, value: 0xC3 0b11000011
Reg: 9, value: 0x5 0b101
Reg: A, value: 0x63 0b1100011 //2 cells
Reg: B, value: 0x0 0b0
Reg: C, value: 0xDC 0b11011100
Reg: D, value: 0x4B 0b1001011
Reg: E, value: 0x3D 0b111101
Reg: F, value: 0xA2 0b10100010
Reg: 10, value: 0x0 0b0 //watchdog disabled
Reg: 11, value: 0x40 0b1000000
Reg: 12, value: 0x0 0b0
Reg: 13, value: 0x1 0b1
Reg: 14, value: 0x36 0b110110 //IBAT discharge current sensing enable for ADC
Reg: 15, value: 0xAA 0b10101010
Reg: 16, value: 0xC0 0b11000000
Reg: 17, value: 0x7A 0b1111010
Reg: 18, value: 0x54 0b1010100
Reg: 19, value: 0x1 0b1
Reg: 1A, value: 0x2C 0b101100 //Input Current Limit obtained from ICO or ILIM_HIZ pin setting decimal 300 * 10mA = 3000mA
Reg: 1B, value: 0xF 0b1111 //No poor source detection, power good, VBUS , AC1&2 present
Reg: 1C, value: 0x6A 0b1101010 //fast charge, Unknown adapter, BC1.2 or non-standard detection NOT complete
Reg: 1D, value: 0x1 0b1 //VBAT present
Reg: 1E, value: 0x0 0b0
Reg: 1F, value: 0x0 0b0
Reg: 20, value: 0x0 0b0
Reg: 21, value: 0x0 0b0
Reg: 22, value: 0x8F 0b10001111
Reg: 23, value: 0x90 0b10010000
Reg: 24, value: 0x40 0b1000000
Reg: 25, value: 0x0 0b0
Reg: 26, value: 0x0 0b0
Reg: 27, value: 0x0 0b0
Reg: 28, value: 0x0 0b0
Reg: 29, value: 0x0 0b0
Reg: 2A, value: 0x0 0b0
Reg: 2B, value: 0x0 0b0
Reg: 2C, value: 0x0 0b0
Reg: 2D, value: 0x0 0b0
Reg: 2E, value: 0x80 0b10000000 //ADC EN, 15 bit effective resolution
Reg: 2F, value: 0x0 0b0
Reg: 30, value: 0x0 0b0
Reg: 31, value: 0x0 0b0
Reg: 32, value: 0x11 0b10001 //IBUS 17mA
Reg: 33, value: 0x0 0b0
Reg: 34, value: 0x0 0b0 // IBAT 0mA
Reg: 35, value: 0x2F 0b101111
Reg: 36, value: 0x27 0b100111 //VBUS 12,071mV
Reg: 37, value: 0x2F 0b101111
Reg: 38, value: 0x31 0b110001 //VAC1 12081
Reg: 39, value: 0x2F 0b101111 
Reg: 3A, value: 0x18 0b11000 //VAC2 12056
Reg: 3B, value: 0x1B 0b11011
Reg: 3C, value: 0x60 0b1100000 //VBUS 7008
Reg: 3D, value: 0x1B 0b11011
Reg: 3E, value: 0x6A 0b1101010 //VSYS 7018
Reg: 3F, value: 0x2 0b10
Reg: 40, value: 0x67 0b1100111 //TS 615
Reg: 41, value: 0x0 0b0
Reg: 42, value: 0x2F 0b101111 //TDIE 47
Reg: 43, value: 0x0 0b0
Reg: 44, value: 0x0 0b0 //D+
Reg: 45, value: 0x0 0b0
Reg: 46, value: 0x0 0b0 //D-
Reg: 47, value: 0x0 0b0
Reg: 48, value: 0x8 0b1000

  • 0 in reply to Michael Potas
    TI__Intellectual 1110 points

    Hi Michael,

    I don't see any obvious issues. Are you using the EVM, if not could you provide a schematic?

    Regards,

    Jared Baxter

  • 0 in reply to Michael Potas
    TI__Guru**** 180216 points

    Hi Michael,

    Is the converter switching, i.e. are there switching pulses on SW1? Does REGN pin have ~ 5V output?  With no power at VBUS and battery not connected to BAT/BAP, can you use a DMM to measure the resistance between SYS and BAT/BATP pins?

    Regards,

    Jeff