AAT3680 Datasheet, PDF (14/18 Pages) Advanced Analogic Technologies – Lithium-Ion Linear Battery Charge Controller

AAT3680
Lithium-Ion Linear Battery Charge Controller
current rating must be for a given blocking diode.
The minimum power handling capacity must be cal-
culated based on the constant current amplitude
and the diode forward voltage (V_F):
Where:
P_D(MIN) = Minimum power rating for a diode selec-
tion
V_F = Diode forward voltage
I_CC = Constant current charge level for the system
P_D(MIN) = V_F / I_CC
Schottky Diodes
The reason for selecting a Schottky diode for this
application is because Schottky diodes have a low
forward voltage drop. The forward voltage (V_F) for
a Schottky diode is typically between 0.3V and
0.4V. A lower V_F permits a lower voltage drop at
the constant current charge level set by the sys-
tem, less power will be dissipated in this element of
the circuit. Schottky diode allow for lower power
dissipation, smaller component package sizes and
greater circuit layout densities.
Rectifier Diodes
Any general purpose rectifier diode can be used
with the AAT3680 application circuit in place of a
higher cost Schottky type diode. The design trade-
off is a rectifier diode has a high forward voltage
drop. V_F for a typical silicon rectifier diode is in the
range of 0.7V. A higher V_F will place a input supply
voltage requirement for the battery charger sys-
tem. This will also require a higher power rated
diode since the voltage drop at the constant current
charge amplitude will be greater. Refer to the pre-
viously stated equations to calculate the minimum
V_IN and diode P_D for a given application.
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3680.2003.4.0.91