MP26124

–24V INPUT, 2A, 600kHz, 4S SWITCHING LI-ION BATTERY CHARGER

MP26124 Rev. 1.0

www.MonolithicPower.com

12

10/10/2017

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© 2017 MPS. All Rights Reserved.

OPERATION

The

MP26124

is

a

peak-current

mode-

controlled switching charger for use with Li-ion

batteries.

At the beginning of a cycle, the MOSFET (M1)

is off, and the COMP voltage is higher than the

output of the current sense amplifier (A1). The

pulse-width modulation (PWM)

comparator’s

output is low, and the rising edge of the 600kHz

CLK signal sets the RS flip-flop, which turns on

M1, connecting SW and the inductor to the

input supply.

As the inductor current increases, the output of

A1 increases. When this signal exceeds the

COMP voltage, the RS flip-flop resets and turns

M1 off. The external switching diode (D2) then

conducts the inductor current.

The MP26124 uses COMP to select the smaller

value of GMI and GMV to implement either

current loop control or voltage loop control.

Current loop control occurs when the battery

voltage is low, which results in the saturation of

the GMV output. 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 MP26124 has an internal linear regulator

(VREF33)

to

power

the

internal

circuitry.

VREF33 can also power external circuitry as

long as the load does not exceed the maximum

current

(30mA).

Connect

a

1

μF bypass

capacitor from VREF33 to GND to ensure

stability.

Charge Cycle (Mode Change: Trickle  CC

 CV)

At the start of a charging cycle, the MP26124

charging cycle starts in trickle-charge mode

(10% of the RS1 programmed constant-charge

If the charge stays in trickle-charging mode until

the time-out condition is triggered, charging

terminates until the input power or EN signal

refreshes. Otherwise, GMI regulates the charge

current to the level set by RS1. The charger

operates at constant-current (CC) charging

mode. The duty cycle of the switcher is

determined by the COMPI voltage, which is

regulated by the amplifier GMI.

When the battery voltage reaches the constant-

voltage mode threshold, GMV regulates COMP

and the duty cycle for constant voltage (CV)

mode. When the charge current drops to 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, the

charging terminates immediately and resumes

when either the input power or EN signal can

restart the charger.

Figure 2 shows the typical charge profile of the

MP26124.

Trickle charge

CC charge

Threshold

CV charge

Threshold

CC charge

CV charge

Charge Full

Trickle

Charge

Current

Constant

Charge

Current

Figure 2: Li-Ion Battery Charge Profile

Automatic Recharge

After the battery has completely recharged, the

charger disables all blocks except for the

battery voltage monitor to limit the leakage

current. If the battery voltage falls below

4.0V/cell, the MP26124 begins recharging with

a soft start. The timer then resets to avoid

timer-related charging disruptions.

Charger Status Indication

The MP26124

has two

open-drain

status

when the IC supply voltage (VCC) exceeds the

under-voltage lockout (UVLO) threshold and the

regulated voltage (VIN) is 300mV higher than