Charger Enable Input

The MAX8844Z/MAX8844Y contain an active-low logic

input (EN) used to enable the chargers. Drive EN low,

leave unconnected, or connect to GND to enable the

charge-control circuitry. Drive EN high to disable the

charger-control circuitry. EN has an internal 200k

Ω pull-

down resistor.

Soft-Start

The soft-start algorithm activates when entering fast-

charge mode. When the prequalification state is com-

ramps up in 250µs to the full charging current. This

reduces the inrush current demand on the input supply.

Applications Information

Fast-Charge Current Setting

The maximum charging current is programmed by an

Use the following equation to determine the fast-charge

Top-Off Current Threshold Setting

The top-off current threshold is programmed by an

Use the following equation to determine the top-off cur-

2.2k

Ω.

Capacitor Selection

Connect a ceramic capacitor from BATT to GND for

proper stability. Use a 2.2µF ceramic capacitor for most

applications. Connect 1µF ceramic capacitors from IN

to GND and from USB to GND. A larger input capacitor

can be used for high charging current to reduce input

voltage ripple.

Connect 1µF ceramic capacitors from SAFEOUT to

GND and from SAFEUSB to GND. A larger bypass

capacitor for SAFEOUT and SAFEUSB can be used for

optimum noise immunity. Ceramic capacitors with X5R

or X7R dielectric are highly recommended due to their

small size, low ESR, and small temperature coefficients.

Thermal Considerations

The MAX8844Z/MAX8844Y are available in a thermally

enhanced TDFN package with an exposed pad.

Connect the exposed pad to a large copper ground

plane to provide a thermal contact between the device

and the circuit board for increased power dissipation.

The exposed pad transfers heat away from the device,

allowing the IC to charge the battery with maximum cur-

rent, while minimizing the increase in die temperature.

I

V

R

FAST CHARGE

SETI

-

=

1250

28V Dual Input Linear Li+ Battery Chargers with

Battery Detection and Overvoltage-Protected Output

______________________________________________________________________________________

11

IN

USB

CHARGER STATE

4.25V

4.25V

Enabled, selects IN power supply

4.25V

Not present

Enabled, selects IN power supply

Not present

4.25V

Enabled, selects USB power supply

≥ 7.5V

4.25V

Disabled

4.25V

≥ 7.5V

Enabled

Table 3. Input Power-Supply Selection