MP2623 – 2A, 24V INPUT, 1.1MHz 1- OR 2-CELL SWITCHING LIFEPO
4
BATTERY CHARGER
MP2623 Rev. 1.0 www.MonolithicPower.com 10
12/26/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2013 MPS. All Rights Reserved.
OPERATION
The MP2623 is a peak-current–mode controlled
switching charger for use with LiFePO
4
batteries.
At the beginning of each cycle, M1 is off and the
COMP voltage exceeds the output of the current-
sense amplifier (A1). The PWM comparator’s
output is low, and the rising edge of the 1.1MHz
CLK signal sets the RS flip-flop that turns on M1;
this connects the SW pin and the inductor to the
input supply.
A1 senses and amplifies the inductor current:
The PWM comparator then compares the sum of
this signal and the ramp compensator signal
against the COMP signal. When the sum of the
A1 output and the ramp compensator exceeds
the COMP voltage, the RS flip-flop resets and
turns M1 off. The external switching diode (D2)
then conducts the inductor current. If the sum of
the A1 output and the ramp compensator does
not exceed the COMP voltage, then the falling
edge of the CLK resets the flip-flop.
The MP2623 uses COMP to select the smaller
value of GMI and GMV to implement either
current-loop control or voltage-loop control.
Current-loop control triggers when the battery
voltage goes low, which results in the GMV
output saturating. The GMI compares the charge
current (as a voltage sensed through RS1)
against the reference voltage to regulate the
charge current to a constant value. When the
battery voltage charges up to the reference
voltage, the output of GMV goes low and initiates
voltage loop control to control the duty cycle to
regulate the output voltage.
The MP2623 has an internal linear regulator—
VREF33—to power internal circuitry. It can also
power external circuitry as long as the load does
not exceed the maximum current (30mA).
Connect a 1F bypass capacitor from VREF33 to
GND to ensure stability.
Charge Cycle (Mode change: Trickle CC
CV)
At the start of a charging cycle, the MP2623
monitors V
BATT
. If V
BATT
is lower than the trickle-
charge threshold, V
TC
(typically 2.52V/cell), the
charging cycle will start in trickle-charge mode
(10% of the RS1-programmed constant-charge
current, I
CC
) until the battery voltage reaches V
TC
.
If the charge stays in the trickle-charge mode
until the time-out condition triggers, charging
terminates and will not resume until either the
input power or the EN signal refreshes.
Otherwise, GMI regulates the charge current to
the level set by RS1. The charger operates in
constant-current–charging mode. The COMPI
voltage—regulated by GMI—determines the
switching duty cycle.
When the battery voltage triggers constant-
voltage mode, GMV regulates the COMP pin and
the duty cycle. When the charge current drops to
the battery-full threshold, I
BF
(typically 10% I
CC
),
the battery is defined as fully-charged, the
charger stops charging, and CHGOK goes high
to indicate the charge-full condition. If the total
charge time exceeds the timer period, charging
terminates at once and will resume when either
the input power or EN signal can restart the
charger.
Figure 2 shows the typical charge profile of the
MP2623.
Trickle charge
CC charge
Threshold
CV charge
Threshold
CC charge CV charge
I
CHG
V
BATT
Charge Full
Trickle
Charge
Current
Constant
Charge
Current
I
BF
Figure 2: Li-Ion Battery Charging Profile
Automatic Recharge
After the battery completely recharges, the
charger removes all the blocks besides the
battery voltage monitor to reduce the leakage
current from the input or the battery. If the battery
voltage drops below 3.42V/Cell, the circuit will
automatically recharge the battery using soft-start.
The timer will then restart to avoid triggering a
false fault.
