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BQ24133: Fast charge timeout when DPM in operation

Ralph Hancock
Prodigy 40 points
Part Number: BQ24133

The fast charge timeout is set by the capacitance at the TTC pin (5.6 min/nF); this would normally be sized according to the attached battery capacity allowing some margin for temperature and ageing of cells.

If the bq24133 is used in a system with high system load current such that DPM throttles back the battery charging current, does the bq24133 adjust the fast charge timer accordingly?  One might account for this in the calculation of the TTC capacitance - however this might give an unduly high timeout in cases with little or no system current.

  • 0
    TI__Genius 14430 points
    Hi Ralph,

    BQ24133 separates system and battery path when Vin is both battery and system power source. When charger is in DPM loop, Fast charge timer period will be 2 times the original period. When there is in Fast charge period, the Fast charge timer period will be normal.

    Best regards,
    Ann Lien
  • 0 in reply to Ann_Lien
    Prodigy 40 points

    Hi Ann,

    Thank you for your reply.  This information does not appear to be in the datasheet.

    Does the increase in fast charge timer period also apply if the parts enters DPM mode but operates with an unremovable battery (as per Figure 22 in bq24133 datasheet)?

    If the battery started charge without DPM active and progressed to say 50% charge before DPM was active (for a short period of time), is the fast charge timer reset or does it carry on from the point it reached before DPM was active?

    If the fast timer period is reset each time the system enters/exits DPM mode the battery could in theory be charged for a prolonged time period; it would seem to be unwise to rely on it as a safety timer.

    Kind regards,

    Ralph

  • 0 in reply to Ralph Hancock
    TI__Genius 14430 points
    Hi Ralph,

    Your opinion is right. There is a prolonged period for the reset operation. For the normal operation, the timer won't be reset for exit or enter DPM loop. Time period would be carried on to next stage.

    Best regards,
    Ann Lien