QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 920
STAND ALONE LI-ION CHARGER WITH SYNCHRONOUS BUCK REGULATOR
2
Power and Charge LEDs indicate charger
status. The Power LED indicates that the input
voltage is greater than the undervoltage lock-
out threshold level.
The Charge LED has three states. With a bat-
tery connected, the LED is on when either
trickle current is flowing (VBAT < 2.9V) or
when charge current greater than 10% of the
programmed value is flowing (VBAT > 2.9V).
When the battery voltage approaches the float
voltage, the charge current will begin to drop.
When it drops below 10%, the Charge LED
goes out, indicating that the battery is near full
charge. Charging continues until the timer
ends the charge cycle. During a trickle charge,
if the battery voltage does not exceed 2.9V af-
ter ¼ of the total charge time, the battery is
considered defective, charging ends and the
Charge LED flashes at a 2Hz rate.
With no battery connected, there is a condition
where the Charge LED will be on with very lit-
tle or no charge current flowing. This occurs
with low input voltage. When the input voltage
exceeds approximately 3.5V, the Power and
Charge LEDs come on. Above 4.3V, the
Charge LED goes off.
The charger jumper (JP1) can be used to shut
down the charger and reset the timer. The
PROG terminal can be used to program differ-
ent charge current and also measure the
charge current anytime in the charge cycle.
The PROG pin voltage is directly proportional
to the charge current where one Volt is equal
to full programmed current.
After the charge cycle has ended, if the battery
voltage drops approximately 100mV, a new
2.25 hour recharge cycle will begin.
The 2.25MHz synchronous buck regulator has
jumper selected output voltages of 1.2V, 1.5V,
1.8V and 2.5V with output current up to
300mA. Jumpers are also provided for low
quiescent current shutdown and for either fixed
frequency or Burst mode operation. Burst
mode provides high efficiency at low load cur-
rent. The input power for the regulator comes
from the BAT pin. Normally, a Li-Ion battery
would be connected to the BAT pin, although
the buck regulator can be operated without a
battery. When no battery is present, some ad-
ditional capacitance on the BAT pin may be
needed. Also, when the termination timer ends,
the BAT voltage will begin to drop. When it
drops below the recharge threshold, the timer
is reset and the charger output voltage returns
to the float voltage of 4.2V.
