MP2605 – 28V, 1A LINEAR BATTERY CHARGER WITH TRICKLE CHARGE AND TIMER
MP2605 Rev. 1.0 www.MonolithicPower.com 9
1/19/2017 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2017 MPS. All Rights Reserved.
OPERATION
Input Voltage Range
The MP2605 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 3.0V or higher than 7.0V.
The open-drain pin
ACOK is used to indicate
an input power good condition (i.e.
3.0V<V
IN
<7.0V). If the input voltage is lower
than the battery voltage, the IC is also disabled
to prevent the battery from draining.
Charge Cycle (Mode Change: Trickle -> CC->
CV)
Figure 2 shows the typical charging profile for
the MP2605. For a fully depleted battery with a
terminal voltage lower than 2.6V, the MP2605
will start with the trickle charge (preconditioning)
at 10% of the full charge current based on the
value of R
CHG
. If the charger stays in trickle
mode longer than 32768 cycles, the battery
fault condition will be indicated by flashing the
CHG LED. After the battery voltage reaches
2.6V, the charger begins charging using the
programmed charge current (I
CHG
).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
current is reduced to 20% of the programmed
constant current value (I
CHG
). The charge
process is then terminated. Recharge will start
after the battery voltage is reduced to 4.0V.
After 262144 cycles of continuous charging, if
the battery still has not reached 20% of the I
CHG
condition, the on-chip timer will terminate the
charger to prevent charging the dead battery
excessively and the fault condition will be
flagged by flashing the
CHG LED.
Charge Termination
The charge current will gradually decrease in
CV mode as the battery approaches full. The
battery full threshold is internally programmed
to be 20% of the I
CHG
. When the charge current
reaches this threshold, the charger IC will be
automatically turned off.
2.6V 4.2V
V
BATT
10% of I
CHG
20% of I
CHG
Trickle
Charging
CC
Charging
Charging
Complete
CV
Charging
I
CHG
I
BATT
Figure 2—MP2605 Typical Charging Profile
Automatic Recharge
When V
BATT
drops to 4.0V, the charger will
automatically restart the charge cycle until the
20% I
CHG
condition is met again. When the input
adapter is unplugged, or the charger is disabled
and/or terminated, the leakage current from the
battery to the MP2605 is less than 1uA.
Programming of Charge Current and Battery
Full Current
The charge current (I
CHG
) is set by a resistor
(R
CHG
) connected from the ISET pin to GND,
)mA(I/1700)k(R
CHGCHG
.
The relationship between the charge current
and the programming resistance is established
by the following table and graph.
Table 1—R
CHG
and I
CHG
Relationship
R
CHG
(kΩ) I
CHG
(mA)
1.65 1000
1.82 900
2.05 800
2.32 700
2.74 600
3.3 500
4.12 400
5.6 300
8.45 200
15 100
