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BQ2000T or BQ2002T

Jeffrey Kleck
Prodigy 20 points
Other Parts Discussed in Thread: BQ2000T, BQ2002T, BQ2002

My design uses a 2-cell NiMH battery pack and a 5V input source for the battery charger.

I have a couple of quesions:

  1. Which would be a better charging IC choice (BQ2000T or BQ2002T)?
  2. Which would be the best choice to isolate the resistor divider on the BAT pin from the battery pack when the 5V input source is removed:
    1. Move input isolation diode from between 5V input source and switching transistor to between the BAT pin's resistor divider and the BAT+ connection?
    2. Add N-channel FET in series with lower resistor in BAT pin's resistor with gate connected to 5V input source?
  • 0
    TI__Guru*** 142750 points

    Either IC will work fine.  The bq2000T is a switching charger while the bq2002 is a linear charger.  It just depends on whether you want a simpler design (bq2002) with more power dissipation in the main transistor (less efficiency).  This would also depend on your fast charge current.

    Disconnecting the voltage divider would only be advantageous if the divider current is significant when compared to the self discharge of the pack.  I'm not sure this is the case.

    I'm not sure that I understand how option 1 would work.  With option 2, you may need to be careful when applying the 5V input source.  If the full battery voltage (not the divided down voltage) is already on the BAT pin when the input voltage is applied, then the IC may go straight to complete charge before the FET turns on.