Linear Li+Battery Charger with Integrated Pass FET

and Thermal Regulation in 3mm x 3mm Thin DFN

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9

Application Circuits

Stand-Alone Li+ Charger

The MAX1507 provides a complete Li+ charging solu-

tion. The Typical Application Circuit on the front page

shows the MAX1507 as a stand-alone Li+ battery

charger. The 2.8kΩ resistor connected to ISET sets a

charging current of 520mA. The LED indicates when

either fast-charge or precharge qualification has

begun. When the battery is full, the LED turns off.

Microprocessor-Interfaced Charger

Figure 3 shows the MAX1507 as a µP-cooperated Li+

battery charger. The MAX1507 starts charging the bat-

tery when EN is low. The µP can drive EN high to dis-

able the charger. Use a logic-biased NPN transistor as

an inverter circuit to generate an AC_ON signal for the

system to detect the presence of an input supply. CHG

can be used to detect the charge status of a battery.

charge current.

USB-Powered Li+ Charger

The universal serial bus (USB) provides a high-speed

serial communication port as well as power for the

remote device. The MAX1507 can be configured to

charge its battery at the highest current possible from

the host port. Figure 4 shows the MAX1507 as a USB

battery charger. To make the circuit compatible with

either 100mA or 500mA USB ports, the circuit initializes

at 95mA charging current. The microprocessor then

interrogates the host to determine its current capability.

If the host port is capable, the charging current is

increased to 435mA. The 435mA current was chosen to

avoid exceeding the 500mA USB specification.

MAX1507

1µF

2.8kΩ

IN

CHG

1µF

4.2V Li+

BATT

EN

GND

SYSTEM

TEMP

VL

ISET

AC/DC

ADAPTER

VI/O

ROHM

DTC114EM

VI/O

AC_ON

CHARGE-CURRENT MONITOR

LOW: CHARGE, HIGH: FULL OR OFF

0.47µF

Figure 3. µP Interfaced Li+ Battery Charger