QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 789
SINGLE CELL LI-ION BATTERY CHARGER WITH COMPARATOR
3
QUICK START PROCEDURE
The charger can be evaluated using an actual Lith-
ium Ion battery or a battery simulator. The battery
simulator is faster because all battery state-of-
charge conditions can be quickly simulated.
A battery simulator consists of an adjustable power
supply with a load resistor across the power supply
output. The resistor value is selected that will pro-
vide approximately 1A when the power supply is set
for 2.5V and the power supply must provide at least
1.7A when adjusted for 4.2V. For this battery simu-
lator, a 2.5 Ohm, 10 Watt power resistor connected
to the output of a 5V, 2A bench supply will work fine.
The power supply can now sink and source current,
similar to a battery, and by changing the power sup-
ply voltage, any battery state-of-charge condition
can be quickly simulated.
Begin evaluation by moving the jumpers to the fol-
lowing positions. Move the TERMINATION METHOD
jumper (JP1) to the ITERM (upper) position to select
minimum charge current termination. Move the IDET
jumper (JP4) to the 100mA (lower) position, the
ICHG-2 jumper (JP2) to the “C” (upper) position and
the ICHG-1 jumper (JP3) to the HIGH (upper) posi-
tion. For this evaluation place the COMP jumper
(JP5) in the BAT (lower) position. The charger is
now set to charge at 1A and use minimum charge
current (IDET = 100mA) for charge termination. The
comparator is set to monitor the battery voltage and
to indicate when the battery voltage drops below
2.910V.
With the input power supply and battery simulator
power supply adjusted to 0V, connect the input
power supply output to the VIN and GND, and the
battery simulator power supply output to the BAT
and GND terminals as shown in Figure 1. An amme-
ter or 100m current sense resistor can be placed
between the BAT terminal and the positive terminal
of the battery simulator to measure charge current.
Connect a 4½ digit DVM to the BAT and GND termi-
nals to measure battery voltage. Begin increasing
the input supply voltage, up to 5V. At approximately
3.8V (undervoltage lockout threshold), the CHRG
LED will turn on and the preconditioning trickle
charge of 100mA (10% of the programed current)
will begin flowing. The COMP LED will be off be-
cause the battery voltage is below 2.910V. Adjust the
battery simulator power supply to 3V. At approxi-
mately 2.9V, the charge current will abruptly in-
crease to the programmed constant current of 1A.
Continue slowly increasing the battery simulator
power supply, thus simulating the Li-Ion battery ac-
cepting charge. As the battery simulator approaches
the float voltage of 4.200V, the charge current will
begin to drop as the charger begins the constant
voltage portion of the charge cycle. It is important to
keep the DC resistance between the charger output
and the battery to a minimum, otherwise the charge
current will begin dropping much sooner. When the
charger is in the constant voltage portion of the
charge cycle, small changes in the simulator power
supply voltage will result in relatively large changes
in charge current. When the charge current drops
below the IDET threshold of 100mA, the charge cur-
rent will drop to 0, the CHRG LED will go off and the
charge cycle will end. When timer termination is se-
lected (using JP1), the CHRG LED will go off when
the charge current drops below 100mA, but the
charge cycle will continue until the 3 hour timer
ends.
After the charge cycle has ended, if the battery volt-
age drops approximately 100mV, a recharge cycle
will begin. A recharge cycle is 50% (1.5 hours) of
the programmed time (provided timer termination is
selected). Reducing the battery simulator down to
approx. 2.910V will result in the comparator to
change states (LED off). The micropower compara-
tor receives power from the battery allowing the
comparator to be active when input power is re-
moved. Other voltages can be monitored by placing
the COMP jumper (JP5) in the EXT (upper) position
and applying the voltage to be monitored to the
COMP IN pin. The internal comparator reference
voltage is 1.00V ± 1.2%, with 50mV of hysteresis.
