BQ24450 Datasheet, PDF (11/20 Pages) Texas Instruments – INTEGRATED CHARGE CONTROLLER FOR LEAD-ACID BATTERIES

bq24450
www.ti.com ..................................................................................................................................................................................................... SLUS929 – APRIL 2009
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V_IN
I_MAX-CHG
I_CHG
I_TAPER
I_PRE
V_BOOST
V_BI
V_FLOAT
V_RCH
V_TH
V_BAT
Figure 6.
Further Improvements to the Circuit of Figure 5
In applications where the load current is very low, the current through the V_BAT voltage divider can be a
non-negligible proportion of the load current. Current flowing back thorough Q_EXT when the input power is
removed constitutes another drainage path. The modifications in Figure 7 fix both these issues.
The addition of D_EXT (see Figure 7) fixes the reverse current problem. Returning the voltage feedback divider
chain to the PGOOD pin instead of to GND ensures that the divider does not draw any current when the input
supply is not present. (When sinking 50µA, the saturation voltage of the PGOOD transistor is typically only
30mV).
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