MP2608- 28V, 1A DUAL INPUT LINEAR BATTERY CHARGER WITH TIMER
MP2608 Rev. 0.9 www.MonolithicPower.com 9
8/29/2008 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2008 MPS. All Rights Reserved.
OPERATION
Input Auto Selection and Voltage Range
The MP2608 is a dual-input charger, when both
input sources are present, MP2608 selects only
one power source to charge the battery. When
the adapter input voltage is higher than the
UVLO threshold, IN is selected as the power
source. Otherwise the USB input is selected. If
both the inputs is above UVLO but the adaptor
input voltage is below the battery voltage, while
the USB voltage is higher than the battery
voltage, then the USB input is used to charge the
battery.
In case there is no power source available or
both the two input are below the UVLO, the
MP2608 is in the sleep mode, in which the
current into the BATT pin is reduced to TBD µA.
The IC is also disabled to prevent the battery
from draining.
The MP2608 has built-in input voltage surge
protection as high as +28V. The charger IC will
be automatically disabled when the input voltage
is lower than 2.5V or higher than 6.0V.
Charge Cycle (Mode Change: Trickle -> CC-> CV)
Figure 2 below shows the typical charging profile
for the MP2608. For a fully depleted battery with
a terminal voltage lower than 2.6V, the MP2608
will start with the trickle charge (preconditioning)
at 10% of the programmed full charge current.
After the battery voltage reaches 2.6V, the
charger begins charging at the constant current
of the programmed value (I
CHG
) and the charge
timer starts counting down. This is referred to as
Constant Current (CC) mode. Once the battery
voltage reaches 4.2V, the charger will operate in
the constant voltage (CV) mode until the battery
is fully charged. The charge current drops during
CV mode, and the battery full indication is set
when the charge timer is time off. The charge
timer is to protect the system from charging a
dead battery for excessive long time.
POWER DISSIPATION
Timer
Charge
End
CV
Mode
CC
Mode
Trickle
Charging
Charge
Start
I
BATT
V
BATT
V
IN
V
CH
V
MIN
I
SET
10% of I
SET
Figure 2—MP2608 Typical Charging Profile
Charge Termination and Auto-Recharge
At any time when V
BATT
is 50mV higher than the
trimmed charge target, the MP2608 reduces its
charge current to 0µA. This ensures the safety of the
battery. Also, the CV control loop always monitors the
battery voltage such that it will automatically recharge
the battery when it is depleted below the target level.
Upon V
BATT
drops to 4.0V, the charger will
automatically restart the charge cycle until the end of
the timeout. When the input adapter is unplugged,
there is only 1µA leakage current from battery drawn
by the MP2608.
Programming of Charge Current and Battery
Full Current
The Charge Current (I
CHG
) of Adaptor input can
be programmed from 0.1A to 1A by a resistor
(R
CHG
) connecting from the ICHG pin to GND.
The relationship of the charge current and the
programming resistance is established by the
following table and graph.
The recommended resistance for programming
the charge current is TBD
.The battery full charge
current threshold (I
BF
)is programmed by
connecting a resistor R
BF
from the I
BF
pin to GND:
I
BF
=1AX1.7kΩ/R
BF
When the USB is selected as the power source, the
charge current is fixed at a pre-set value 450mA,
which is a typical value of USB current.
