MP2610 – 2A, 24V INPUT, 1.1MHz 1-2CELL SWITCHING LI-ION BATTERY CHARGER
MP2610 Rev. 0.91 www.MonolithicPower.com 9
7/13/2010 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
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OPERATION
The MP2610 is a peak current mode controlled
switching charger for use with Li-Ion batteries.
Figure 2 shows the block diagram. At the
beginning of a cycle, M1 is off. The COMP
voltage is higher than the current sense result
from amplifier A1’s output and the PWM
comparator’s output is low. The rising edge of the
1.1MHz CLK signal sets the RS Flip-Flop. Its
output turns on M1 thus connecting the SW pin
and inductor to the input supply.
The increasing inductor current is sensed and
amplified by the Current Sense Amplifier A1.
Ramp compensation is summed to the output of
A1 and compared to COMP by the PWM
comparator.
When the sum of A1’s output and the Slope
Compensation signal exceeds the COMP voltage,
the RS Flip-Flop is reset and M1 is turned off.
The external switching diode D2 then conducts
the inductor current.
If the sum of A1’s output and the Slope
Compensation signal does not exceed the COMP
voltage, then the falling edge of the CLK resets
the Flip-Flop.
The MP2610 have two internal linear regulators
power internal circuit, VREF33 and VREF25. The
output of 3.3V reference voltage can also power
external circuitry as long as the maximum current
(50mA) is not exceeded. A 1F bypass capacitor
is required from VREF33 to GND to ensure
stability.
The output of 2.5V reference voltage can not
carry any load, and it can only be a voltage
reference, like connecting it to the gate of a
MOSFET.
In typical application, VREF25 should be float
and no capacitor is required. It can only connect
to a capacitor which is smaller than 100pF.
Charge Cycle (Mode change: TrickleÆ CCÆ
CV)
The battery current is sensed via RS1 (Figure 2)
and amplified by A2. The charge will start in
“trickle charging mode” (10% of the RS1
programmed current I
CC
) until the battery voltage
reaches 2.8V/cell. If the charge stays in the
“trickle charging mode till “timer out” condition is
triggered, the charger is terminated. Otherwise,
the output of A2 is then regulated to the level set
by RS1. The charger is operating at “constant
current charging mode.” The duty cycle of the
switcher is determined by the COMPI voltage
that is regulated by the amplifier GMI.
When the battery voltage reaches the “constant
voltage mode” threshold, the amplifier GMV will
regulate the COMP pin, and then the duty cycle.
The charger will then operate in “constant voltage
mode.”
Automatic Recharge
1 minute after the battery charging current drops
below the termination threshold, the charger will
cease charging and the
CHGOK pin becomes an
open drain. If for some reason, the battery
voltage is lowered to 4.0V/Cell, recharge will
automatically kick in.
Charger Status Indication
MP2610 has two open-drain status outputs:
CHGOK and ACOK . The ACOK pin pulls low
when an input voltage is greater than battery
voltage 300mV and over the under voltage
lockout threshold.
CHGOK
is used to indicate the
status of the charge cycle. Table 1 describes the
status of the charge cycle based on the
CHGOK
and
ACOK outputs.
Table 1―Charging Status Indication
ACOK CHGOK
Charger status
low low In charging
low high End of charge
high high
Vin < UVLO, thermal
shutdown, timer out,
EN
disable
Timer Operation
MP2610 uses internal timer to terminate the
charge if the timer times out. The timer duration
is programmed by an external capacitor at the
TMR pin.
The trickle mode charge time is:
