• State TI Thinks Resolved
  • Locked Locked
  • Replies 12 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 289 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

BQ25792: BQ25792 About default charge current

BQ25792: BQ25792 default charging current is incorrect

Michael Chu
Prodigy 80 points
Part Number: BQ25792
Other Parts Discussed in Thread: EV2400

Tool/software:

Hi,

I'm using BQ25792EVM board.

Set PROG to 1S, 2A, 1.5Mhz.

Set ILIM_HIZ to 3A. (changed EVM board R21 to 43K)

Connected ACDRV1, 2 to GND.

Connected JP7 (USB_VIN to VAC1)

Connected JP3 (VAC1 to VBUS)

 

Connecting EV2400,

The REG03 shows the charge current 2000mA

The REG1C shows fast charging and 3.25A

Enabled ADC (REG2E)

But the REG33 shows 1300mA. I also used current proble double checked it. the max Charging current is around 1300mA.

I also tried setting REG11, EN 9V, and HVDCP. the max charging current still around 1300mA.

We discharged the battery before the test.

Why is the charging current not 2A? What did I miss?

  • 0
    TI__Guru**** 167196 points

    Hi Michael,

    What do the other status and fault registers from REG0x1B to REG0x27 report?  Is the voltage at VBUS = voltage at the power supply or is the charger in VINDPM?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 80 points

    Hi Jeff,

    I didn't see any fault status. I used 20W USB adapter.

    Attached some screenshots.

     

  • 0 in reply to Michael Chu
    TI__Guru**** 167196 points

    Hi Michael,

    The charger is in VINDPM meaning the charger has clamped the max input current to prevent VBUS from drooping further. The input voltage dropped to the VINDPM threshold when it pulled IBUS=1116mA from the power supply connected at VBUS.  If the power supply provides 5V at its output, the cable connecting to charger VBUS has R = (5V-4.37V)/1.116A = 0.54 ohm of resistance.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 80 points

    Hi Jeff,

    The default setting of VINDPM threshold is 3.6V. In the worset case, the VBUS should be 5 - 2 x 0.54 = 3.92V. The voltage is still higher than 3.6V.

    I also tried enabling HVDCP mode. and set VBUS to 9V. The measurement of VBUS is 8.6V. But max battery charging current is still around 1.3A. 

    It is very strange.

  • 0 in reply to Michael Chu
    TI__Guru**** 167196 points

    HI Michael,

    At VBUS=8.6V, what do the registers report?  

    Are you using an EVM or your own board?  If your own board, did you follow the layout recommendation in the datasheet and EVM, specifically the placement of the 0.1uF decoupling caps on PMID and SYS?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 80 points

    It is TI EVM board.

  • 0 in reply to Michael Chu
    Prodigy 80 points

    Attached regigsters report. 

  • 0 in reply to Michael Chu
    TI__Guru**** 167196 points

    Hi Michael,

    With VBUS=8.88V, the battery is almost fully charged at VBAT=4.189V.  The charger has entered constant voltage mode and the charge current is tapering down as reported in the charge status register.

    In both cases the charger is working as expected.

    Regards,

    Jeff  

  • 0 in reply to Jeff F
    Prodigy 80 points

    Hi Jeff,

    No, the 4.189V is the charging voltage. 

    When removing charging cable, the measurement of battery voltage is 3.757V. The battery hasn't been fully charged yet.

  • 0 in reply to Michael Chu
    TI__Guru**** 167196 points

    HI Michael,

    The ADC measures the voltage at BATP, which is the CV loop regulation point.  The charger thinks the battery is charged due to the additional voltage drop across your cable and so charge current has started tapering down.  The resistance from the BATP pin to battery is (4.189V-3.757V)/1185mA = 364mohm.  With lower resistance cables on input and output, the charger will provide 2A charge current.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 80 points

    Hi Jeff,

    I don't get your caculation - (4.189V-3.757V)/1185mA = 364mohm.. 

    If I charge the battery from 2.5V or 3V, the resistance from the BATP pin to battery will be much higher.

    Actually, I found something interesting. When I charge the battery from 3.5V or less, I did see the chargering current went to 1.9A. 

    Looks the charger has some kind of strategies to charge the battery. The charging current is dropping when battery voltage inceasing.

  • 0 in reply to Michael Chu
    TI__Guru**** 167196 points

    Hi Michael,

    The ADC is reporting what I expect.  In the first case, the charger is limited by input power (current) due to VINDPM.  A 5V supply is attached but VBUS is regulated to 4.384V per ADC which agrees with the VINDPM 4.3V register.  In the second case, the battery voltage at BATP sense point per ADC is at 4.189V which is close to VREG=4.2V and the charge status is in taper so current has started tapering down to termination.  When you lower the battery voltage, less input power is needed for 2A charge current.  If you use a multimeter to measure the voltage at the battery terminals and from EVM BATP pin to GND, you will see difference.  Alternatively, you can power down, disconnect the battery and measure the cable resistance or the measure the input cable resistance with the multimeter set to measure resistance.

    Regards,

    Jeff