LTC4002_15 Datasheet, PDF (10/16 Pages) Linear Technology – Standalone Li-Ion Switch Mode Battery Charger

LTC4002
TEST CIRCUITS
Test Circuit 1
15V
–
1.5V
LT1006
+
0V
COMP
100µA
CA
SENSE
R_SENSE
BAT
10Ω
1mA
VA
LTC4002
4.2V
4002 TC02
Test Circuit 2
15V
–
1.5V
LT1006
+
0V
LTC4002
COMP
100µA
CA
SENSE
R_SENSE
BAT
10Ω
V_BAT
4002 TC01
U
OPERATIO
The LTC4002 is a constant current, constant voltage
Li-Ion battery charger controller that uses a current mode
PWM step-down (buck) switching architecture. The charge
current is set by an external sense resistor (R_SENSE)
across the SENSE and BAT pins. The final battery float
voltage is internally set to 4.2V per cell. For batteries like
lithium-ion that require accurate final float voltage, the
internal 2.465V reference, voltage amplifier and the resis-
tor divider provide regulation with ±1% accuracy.
A charge cycle begins when the voltage at the V_CC pin rises
above the UVLO level and is 250mV or more greater than
the battery voltage. At the beginning of the charge cycle,
if the battery voltage is less than the trickle charge thresh-
old, 2.9V for the 4.2 version and 5V for the 8.4 version, the
charger goes into trickle charge mode. The trickle charge
current is internally set to 10% of the full-scale current. If
the battery voltage stays low for 30 minutes, the battery
is considered faulty and the charge cycle is terminated.
When the battery voltage exceeds the trickle charge thresh-
old, the charger goes into the full-scale constant current
charge mode. In constant current mode, the charge cur-
rent is set by the external sense resistor R_SENSE and an
internal 100mV reference; I_BAT = 100mV/R_SENSE.
When the battery voltage approaches the programmed
float voltage, the charge current will start to decrease.
When the current drops to 25% (4.2 version) or 10% (8.4
version) of the full-scale charge current, an internal com-
parator turns off the internal pull-down N-channel MOSFET
at the CHRG pin, and connects a weak current source to
ground to indicate a near end-of-charge condition.
An internal 3 hour timer determines the total charge time.
After a time out occurs, the charge cycle is terminated
and the CHRG pin is forced high impedance. To restart
the charge cycle, remove and reapply the input voltage or
momentarily shut the charger down. Also, a new charge
cycle will begin if the battery voltage drops below the
recharge threshold voltage of 4.05V per cell.
When the input voltage is present, the charger can be shut
down (I_CC = 3mA) by pulling the COMP pin low. When the
input voltage is not present, the charger goes into sleep
4002f
10