MP2618 MPS, MP2618 Datasheet - Page 11

• Manufacturer Part Number: MP2618
• Description: 2a, 24v Input, 600khz 2-3 Cell Switching Li-ion Battery Charger With System Power Path Management
• Manufacturer: MPS

OPERATION
The MP2618 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
600 kHz 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
voltage, the RS Flip-Flop is reset and M1 turns
off. The external switching diode D1 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 MP2618 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 1µF bypass capacitor
is required from VREF33 to GND to ensure
stability.
Charge Cycle (Mode change: Trickle
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 R
programmed current I
reaches 3V/cell. If the charge stays in the “trickle
charging mode” till “timer out” condition triggered,
and the charge 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.
MP2618 Rev. 0.92
7/14/2010
MP2618 – 2A, 24V INPUT, 600kHz 2-3CELL SWITCHING LI-ION BATTERY CHARGER
signal
MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
CC
) until the battery voltage
exceeds
the
© 2010 MPS. All Rights Reserved.
www.MonolithicPower.com
COMP
CC
SEN
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
Once the battery charging current drops below
the termination threshold, the charger will cease
charging and the
drain. If for some reason, the battery voltage is
lowered to 4.0V/Cell, recharge will automatically
kick in.
Charger Status Indication
MP2618 has two open-drain status outputs:
when an input voltage is greater than battery
voltage 300mV and over the under voltage
lockout threshold.
status of the charge cycle. Table 1 describes the
status of the charge cycle based on the
Timer Operation
MP2618 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:
The total charge time is:
CHGOK
CHGOK
ACOK
high
low
low
Table 1―Charging Status Indication
and ACOK outputs.
and ACOK . The ACOK pin pulls low
T
T
TICKLE_TMR
TOTAL_TMR
CHGOK
high
high
low
CHGOK
CHGOK
=
=
Charger status
In charging
End of charge, NTC fault,
timer out, thermal
shutdown
V
V
30mins
3hours
IN
IN
<UVLO
–V
pin becomes an open
is used to indicate the
BAT
×
×
<0.3V.
0.1uF
0.1uF
C
EN
C
TMR
TMR
disable
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