Linear Li+ Battery Charger with Integrated Pass FET

and Thermal Regulation in 3mm x 3mm Thin DFN

8

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EN

CHG

STATE

0

Hi-Z

Shutdown

Low

4.25V

< 2.5V

Low

Prequalification

Low

4.25V

≥ 2.5V

Low

Fast Charge

Low

4.25V

4.2V

Hi-Z

Full Charge

Low

>7V

X

0

Hi-Z

Overvoltage

High

X

X

0

Hi-Z

Disabled

X = Don’t care.

Table 1. CHG States

CHG Charge Indicator Output

CHG is an open-drain current source for indicating

charge status. Table 1 describes the state of

CHG dur-

ing different stages of operation.

CHG is a nominal 12mA current source suitable for dri-

ving a charge-indication LED. If the MAX1507 is used

in conjunction with a microprocessor, a pullup resistor

to the logic I/O voltage allows

CHG to indicate charge

status to the µP instead of driving an LED.

Soft-Start

An analog soft-start algorithm activates when entering

fast-charge mode. When the prequalification state is

ramps up in 3ms to the full charging current. This

reduces the inrush current on the input supply.

Applications Information

Charge-Current Selection

The maximum charging current is programmed by an

Ω

also be used to monitor the fast-charge current level.

The output current from the ISET pin is 0.958mA per

amp of charging current. The output voltage at ISET is

proportional to the charging current as follows:

The voltage at ISET is nominally 1.4V at the selected

fast-charge current, and falls with charging current as

the cell becomes fully charged.

Thermal-Regulation Selection

Set the regulated die temperature of the MAX1507 with

the TEMP three-level logic input. The MAX1507

reduces the charge current to limit the die temperature

to the value set by TEMP. The MAX1507 operates nor-

mally while the thermal loop is active. An active thermal

loop does not indicate a fault condition. TEMP allows

the MAX1507 to maximize the charge current while pro-

viding protection against excessive power dissipation.

Connect TEMP to GND to regulate the die temperature

at +90°C. Leave TEMP floating to regulate the die tem-

perature at +100°C. Connect TEMP to VL to regulate

the die temperature at +130°C.

Capacitor Selection

Connect a ceramic capacitor from BATT to GND for

proper stability. Use a 1µF X5R ceramic capacitor for

most applications.

Connect a 1µF ceramic capacitor from IN to GND. Use

a larger input bypass capacitor for high input voltages

or high charging currents to reduce supply noise.

Connect a 0.47µF ceramic capacitor from VL to GND.

Thermal Considerations

The MAX1507 is in a thermally enhanced thin DFN

package with exposed paddle. Connect the exposed

paddle of the MAX1507 to a large copper ground plane

to provide a thermal contact between the device and

the circuit board. The exposed paddle transfers heat

away from the device, allowing the MAX1507 to charge

the battery with maximum current, while minimizing the

increase in die temperature.

DC Input Sources

The MAX1507 operates from well-regulated DC

sources. The full-charging input-voltage range is 4.25V

to 7V. The device can stand up to 13V on the input

the MAX1507 stops charging.

An appropriate power supply must provide at least

4.25V when sourcing the desired peak charging cur-

rent. It also must stay below 6.5V when unloaded.