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Stand-alone charger with configurable "max charge", i.e. stop at 70%

Dav01
Expert 2300 points
Other Parts Discussed in Thread: BQ24172, BQ24650, BQ24040, BQ21040, BQ25071, BQ24105

Hi,

Since TI has hundreds of charger IC's. I need some help picking a suitable charger with the following specs:

Use-case:
- charging station for single-cell 4.2V Li-Po packs (<1000mAH size packs)

Requirements:
- Must work standalone, no need for i2c/cpu
- configurable charge current, in this application ~500mA for 1C
- configurable max-charge threshold, i.e. stop at 3.9V (related to shipping, the cells must not charge to 100%)
- led indication for charging vs done

Please advice!

  • 0
    TI__Guru**** 167066 points
    The only standalone switching charger ICs that have charge voltage configurable which external resistors are the bq24172 and bq24650 and other bq246xx family members.
  • 0 in reply to Jeff F
    TI__Guru* 75906 points
    TI also has a few linear chargers that may work in this power range, bq24040 and bq21040.
    But none will meet 3.9V charge requirement. An external circuit would be required to stop charge at 3.9V.

    If 3.7V is good enough the BQ25071 may be an option. This is a LiFePO4 charger, profile is similar to Li-Ion but when voltage reaches 3.7V it goes to charge complete, see figure 8 of data sheet. Need to look at this closer if you think it is an option.
  • 0 in reply to Bill Johns
    Expert 2300 points

    Hi Jeff / Bill,

    Thanks for input. I'll take a look at both parts. I believe my wanted stop voltage would be 4.0V
    One idea would be a comparator to simply pull EN low, but to properly measure the "open-circuit" voltage,
    I guess I'd first have to disable charging, or could I simply assume the charge voltage to be about ~200mV above?

    I also looked ad BQ24105 which has  a voltage-divider, Vbat-VFB-GND, I think this might also be an option,
    drawback might be that the charger will enter CV and charge slower at the end (even though it's not needed as my cell is 4.2)

    /d

  • 0 in reply to Dav01
    Expert 2300 points
    one more thing, bq24040 looks ok, but not sure how to configure the charge-voltage cut-off..!?
    it has a PRE_TERM – Pre-Charge and Termination Programmable Threshold, not sure how that would be used.
  • 0 in reply to Dav01
    TI__Guru* 75906 points
    To turn off IC pull the TS pin low.
    You would need an external circuit to limit charge voltage, could be based on TPS389X IC that would control the TS pin.