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Original question:

BQ24105-Q1: How to use BQ24105-Q1 for NiMH charging without using an external MCU

BQ24105-Q1: About charge NiMH at <0.5C rate and terminate with only a safety timer

Koji Hayashi92
Mastermind 7030 points
Part Number: BQ24105-Q1
Other Parts Discussed in Thread: BQ2000,

Hi TI-team

My customer have question.

>It is generally acceptable to charge NiMH at <0.5C rate and terminate with only a safety timer.

Regarding the above answer.

Please tell me the reason for "charge NiMH at <0.5C rate ".

Does "terminate with only a safety timer" mean the following ?

1.This means that the charging is terminated by the flow of the red arrow in the figure below, which means that the charging is not determined by ITERM detection.

2.If the 1 is correct, it will be Fault Condition on the flow if it is terminated by Safety timer, but it is not a problem because it can charge for the time as designed.

3.If VOREG> = VBAT before the set Safety timer, charging will be terminated by ITERM detection.

 VOREG should be set according to the characteristics of the battery to be used so that VOREG> = VBAT does not come before the Safety timer.

 

Best Regards,

Koji Hayashi

  • 0
    TI__Guru**** 166006 points

    Hi Hayashi-san,

    NiMH battery manufacturers recommend terminating with either dV/dt or dT/dt where V is battery voltage and T is battery temperature when fast charging (typically >0.5C) NiMH.  dV/dt or dT/dt termination is difficult.  The only TI charger than can do ti without host software and ADC is the BQ2000 family.  For 0.5C or less charging, it is generally acceptable (check with NiMH manufacturer) to slow charge and terminate using a safety timer only.  The statements above regarding ITERM and VOREG not factoring into termination when using safety timer are correct.  BQ24105-Q1 is an automotive switching charger with external capacitor to set the safety timer.

    Regards,

    Jeff