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BQ24105 - to charging NIMH battery

Mario Kobelke
Prodigy 30 points
Other Parts Discussed in Thread: BQ24105, BQ24115

We are using BQ24105 for charging 3 x NIMH battery 1,2 V in series with capacity of 2700mAh
Design Decision: addional feature to BQ24115 - TTC, STAT2

The following charging parameters are set:
RISET1=20kΩ (500mA),
RISET2=15kΩ (65mA),
FB Resistor devider to VBAT 102kΩ/81kΩ (4,75V VOREG)
TS Resistor devider to VTSB 10kΩ/10kΩ (1,581V) to disables the temperature-sensing feature
C(TTC) capacitor 150nF

When the fast charging is enabled, the max charging current starts with 210mA even with a drained battery.

When the charge current fall below the charge termination current, the status do not change to state Charge complete STAT1 OFF / STAT2 ON

Please comment on this observation.

  • 0
    TI__Guru 56650 points

    1. Please measure the voltage across SNS pin and BAT pin. Also, measure the votlage across the output sense resister. To make sure no voltage difference from the charge current sense resister to the IC pins.

    2. After the current is lower than the termination current, please check TTC? Do we pull it down to ground or pull up to reference?

  • 0 in reply to Wang5577
    Prodigy 30 points

    to 1.)

    Many thanks for your response.

    I have measured the following voltage:

    The difference of the voltage across the shunt (0,1Ohm) to the IC pin SNS - BAT pin is 4mV

    I have swapped the following resistance values:

    FB Resistor devider to VBAT 102kΩ/91kΩ (4,40V VOREG)

    TS Resistor devider to VTSB 4k99Ω /10kΩ (2,10V) to disables the temperature-sensing feature

    RISET2=6k8Ω (ITERM 147mA)

    When the fast charging is enabled, the max charging current starts with 460mA even with a drained battery. --> My opinion is that the influence of the change the resistance TS Resistor to 4k99Ω.

    The current regulation phase is however ended already at ca. 4,1V instaed at the set voltage VOREG to 4,4V. The charging current is already reduced from this voltage and it starts the Voltage Regulation and Charge Termination Phase.

    to 2. Now, after the charge current is lower than the termination current the status do change to state Charge complete STAT1 OFF / STAT2 ON

    Please comment on this observation.

  • 0 in reply to Mario Kobelke
    Guru 13040 points
    Mario, were you able to successfully implement your charger for 3xNiMH?

    I created this thread to question about 4xNiMH, and should yourself or other posters be able to give me an input, it will be much appreciated.
    e2e.ti.com/.../569393

    Regards