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BQ24773 - Extremely Slow Charging

sarkis kazarian
Prodigy 220 points
Other Parts Discussed in Thread: BQ24773

I am using BQ24773 in a circuit that has:
-Micro USB port for charging, driven by a benchtop linear supply capable of supporting 2A (current limit at 2.1A) at 5.05V DC

- Battery pack, using  4 x 18650, Panasonic cells, NCRE18650BE, which are configured 1S 4P, with our safety circuit including PTC fuse and SMTl fuse (non resettable) and independently monitor an I2C temperature sensor on the battery.

So this is a 3.2A x 4 = 12.8A total capacity, of which 8A is usuable running to 3.2V.

When the system is in hibernation, the total current draw is 50nA from the Vsys port.

The charge time is excruciatingly long - ~30 hours for full charge.

The system is set to have the WDT disabled, 2A charge current, 3.2V minimum. Monitoring the charge control registers, it seems to be working normally.

I should mentioned the circuit is nearly identical to the evaluation module - in component choice and layout. The only variation is I am using a 3.3uH inductor instead of the 2.2uH inducator due to part availability.

Why is the charge time so long? How do I improve this? I would expect to see a full charge, which I designate as 3.2V when 'fully depleted' to 4.2V 'fully charged' - 8 A/h, tobe approximately 5 - 6 hours with loss?

30 hours is not acceptable.

  • 0
    TI__Guru 56650 points

    What is the charging current when you have 30 hours charging time?

  • 0 in reply to Wang5577
    Prodigy 220 points

    Measuring approx 150mA across the battery resistor - 0.010 ohm resistor.

    I have a total system consumption when all peripherals are active of 0.8A.

    The current limit is programmed @ 2.0 = I2C registers 0x0A, 0x0B are 0x00 and 0x02 (0x0200) which I calculate to be 2.048. I changed to 0x0400 - no effect.

    I monitor IADP/IBAT/PMON using on board adc, they are

    IADP = 0.550V

    IBAT = 0.020V

    PMON = 0.080V

    All three are enabled, gain at highest option, and the IBAT is set to monitor charge voltage

  • 0 in reply to sarkis kazarian
    Prodigy 220 points

    No replies for a few days - does this mean the part does not work as advertised?

  • 0 in reply to sarkis kazarian
    TI__Guru 56650 points
    "Why is the charge time so long? How do I improve this? I would expect to see a full charge, which I designate as 3.2V when 'fully depleted' to 4.2V 'fully charged' - 8 A/h, tobe approximately 5 - 6 hours with loss? 30 hours is not acceptable."
    150mA charger current for 4x3.2AH battery, how many hours do you think the battery can be charged up? 4x3.2A/0.15A=84hour
    For such small current, 30hours charging time may not be enough.

    Please increase the input source current rating.