QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920
STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR
3
Figure 1. Demonstration Circuit Test Setup
The charger section can be evaluated using an
actual Lithium Ion battery or a battery simulator.
The battery simulator is faster because all bat-
tery state-of-charge conditions can be quickly
simulated.
Battery Simulator
A battery simulator consists of an adjustable
power supply with a load resistor across the
power supply output. The load resistor allows
the battery simulator to source and sink current,
similar to an actual battery. Any battery state-of-
charge condition can be quickly simulated by
simply changing the power supply output volt-
age. The load resistor value is selected that will
sink at least 500mA when the power supply is
set for 2.5V and the power supply must provide
at least 850mA when adjusted for 4.2V. For this
battery simulator, a 5 Ohm, 5 Watt power resis-
tor connected to the output of a 5V, 1A bench
supply will work fine.
Battery Charger
Begin circuit evaluation by moving the jumpers
to the appropriate positions. With the input
power supply and battery simulator power
supply adjusted to 0V, connect the demonstra-
tion circuit as shown in Figure 1.
Begin increasing the input supply voltage, up
to 5V. At approximately 3.6V (the undervoltage
lockout threshold), the Power and Charge
LEDs will turn ON and the preconditioning
trickle charge of 50mA will begin flowing into
the battery or battery simulator. The PROG pin
voltage (Voltmeter V1) will measure 100mV
indicating 10% of the programmed current. Ad-
just the battery simulator power supply to 3V
as measured by V2. At approximately 2.9V, the
charge current will abruptly increase to the
programmed constant current of 500mA. Volt-
meter V1 will measure 1 Volt and V3 will
measure 50mV indicating full charge current is
