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BQ24600: Charging suspended

Yusuf KAYA
Intellectual 630 points
Part Number: BQ24600

Hi,

I have designed a charger circuit nearly the same as application circuit shown at bq24600 datasheet. Differences iare below,

R2: Placed 887k and 909k in parallel instead of 900K resistor

Q4, Q5: CSD18542 mosfets are placed instead of SiR426 Mosfets

RT1: 10K resistor is placed instead of 10k thermistor (For testing only)

When I connect the 28V input voltage, measurements are below, (no battery)

VCC: 27.40V

VFB: 2.20 to 2.48V

REGN: 5.97V

VREF: 3.29V

VIN: 28V

VOUT: 11.48V 

D4 / PG: ON

D3 / STAT: Blinking (0.5Hz)

When i connect 5-S Li-Ion battery pack to charger, it does not charge the battery. However, the charger can charge the 1-S and 2-S Li-Ion battery with 470mA and 300mA respectively. And i think it is normal when we take the output voltage into account.

I also have short videos showing the signals on the gates of the mosfets. I can share them and pcb images with you if they help you analyze the design easier.

Would you please share your thoughts about the problem.

Best regards.

  • 0
    TI__Mastermind 24075 points

    Hi Yusuf,

       Voltage on VFB pin is regulated internally to 2.1V, which corresponds to the battery max charge regulation voltage. The resistor divider at the VFB pin, sets the charge regulation voltage. You will need to change the resistor divider to account for what battery voltage you are using, so you will not be able to test multiple cell configurations with the same resistor divider network.

    For STAT flashing, please capture STAT, VCC, SRN and PH.

  • 0 in reply to Kedar Manishankar
    Intellectual 630 points

    Hi Kedar,

    I replaced the 100k R1 resistor with 50k and got 20.8V output voltage, 2.8A output current for 5-s Li-Ion battery pack. Charging process was completed at 400mA approx. Mosfet surface temperature has reached up to 67C max.

    I think everything is ok. I might need a few optimisation only.

    Can you share your comments about the results of my experiment?

    Thank you.

  • 0 in reply to Yusuf KAYA
    TI__Mastermind 24075 points

    Hi Yusuf,

       One issue with the results is the actual voltage of the VFB pin. It should not rise above 2.1V, if battery voltage is under charging regulation voltage set by the resistor divider at VFB. If battery is above 104% of VFB then this would trip the battery overvoltage comparator and you would observe no charging, as this is a fault condition.

    With regards to the current, this depends on if you are in CC or CV charging modes, as current is only regulated to your fast charge current setting when in CC mode, while current is not regulated and only output voltage is regulated in CV mode. So if battery is close to fully charged then current can vary.

    By everything is okay, do you mean that you see no issues with charging?