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Battery recovery from deep discharge using BQ24055

James Holmes
Prodigy 40 points
Other Parts Discussed in Thread: DRV2605

Hi,

We've been using the BQ24055 with a number of cells and recently encountered an issue relating to deep discharge condition.

If the cell becomes deeply discharged, the PCM on the battery pack kicks in in undervoltage at around 2.5V. After this event, is is not possible to revive and re-charge the cell using BQ24055 - the pack must be removed from the assembly and revived (carefully) using a power supply by applying ~3V with limited current. After reviving the pack (PCM allows connection again), it can be charged with the BQ24055 as normal.

This does not appear to be an issue with all packs, and is presumably an interaction between the PCM and the BQ24055. Are there any suggested methods to revive a deeply discharged cell with the BQ24055 in circuit?

  • 0
    TI__Guru*** 148865 points

    Can you provide the OUT pin voltage and current (also the IN pin current) when a deeply discharged cell is attached?  This IC should provide a 10 mA trickle charge to close the protector. 

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff,

    Thanks for the response. The charger does pull 10mA from the charger IN supply, but the voltage at the battery terminals (connected to OUT) raises to only 245mV.

    D+ and D- are shorted  and TS is tied to ground via a 10k resistor in this configuration should this have any effect...

  • 0 in reply to James Holmes
    TI__Guru*** 148865 points

    Does your battery datasheet tell you how much current the protector requires to get VOUT > 1V since it appears to need more than 10mA?   Is there a host alive even though battery is depleted that could turn on extra current source, disconnect the protector via a switch, etc?

  • 0 in reply to Jeff F
    Prodigy 40 points

    Having investigated further, the pack will recover with 10mA, but there is another device run from the battery (DRV2605) which is drawing the lion's share of the 10mA and preventing the pack from recovering.

    Looking at the datasheet there is no way to adjust the 10mA level for the BQ24055 so I have modified the circuit to disconnect the DRV2605 when the cell voltage drops though this does increase BOM cost.