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BQ25172: Regarding overcharge prevention in timer-based charging

Kyohei
Expert 1500 points
Part Number: BQ25172
Other Parts Discussed in Thread: BQ2002

Tool/software:

Hi team,

Since the BQ25172 uses a timer-based charging method, we believe there may be concerns about overcharging.
Given that the minimum safety timer duration is 4 hours, the maximum charge current that can be set would be around 0.25C.
Would it be correct to assume that at this level, the risk of overcharging is extremely low?
We understand that there is also a protection feature via VOUT_OVP, but during normal voltage rise, the voltage reaches 1.70V, which we believe already indicates an overcharged state.

Best regards,

Kyohei

  • 0
    TI__Guru** 105770 points

    Hello Kyohei,

    Our device expert is OOO this week and will return next week. I will let him comment on the OVP range for NiMH.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 1500 points

    Hi team,

    Would it be possible for someone to confirm this question?

  • 0 in reply to Kyohei
    TI__Guru* 76016 points

    Hello Kyohei

    To prevent overcharge the BQ25172 will check the battery voltage at start of charge cycle, if the battery voltage is above V-RECHG the battery is considered full, and no charge is started.  When the battery voltage falls below V-RECHG the device will begin charging.  V-REHG is 1.33 V / cell, this is also the voltage used for intermittent charging to replenish the cell form natural self-discharge.

    The BQ25172 is not a fast charge device similar to the BQ2002 the charge current, as you noted will be C/4 or lower.  At lower currents NiMH are very tolerant of additional charge current. 

    We collaborated with a major NiMH supplier in the design of the BQ25172 charging profile, it has been evaluated and approved by them.