6

FN6435.0

February 25, 2008

Typical Application Circuit

Theory of Operation

When a valid input voltage is applied at VIN, the ISL9301

first regulates VOUT at 4.5V for system power need. In the

mean time, if the battery is attached, the ISL9301 also

charges the battery while supplying current to the system.

When the system exceeds the maximum available current,

either limited by the IC or by the input power supply, the

charger FET is operated in a reverse mode, i.e. it discharges

current to the system instead of charging.

The charger function is similar to other Li-ion battery

chargers, i.e. it charges the battery at a constant current

(CC) or a constant voltage (CV) depending on the battery

Circuit” on page 6. The constant voltage is fixed at 4.2V. If

the battery voltage is below a typical 2.8V trickle charge

threshold, the ISL9301 charges the battery with a trickle

current (~16% of the programmed constant current) until the

battery voltage rises above the trickle charge threshold.

When the battery voltage reaches the final voltage of 4.2V,

the charger enters the CV mode and regulates the battery

voltage at 4.2V to fully charge the battery without the risk of

overcharging. Upon reaching an end-of-charge (EOC)

current, the charger indicates the charge completion with the

CHG pin, but the charger continues to deliver 4.2V at the

VBAT pin until the timeout limit has reached. Figure 1 shows

the typical charge profile with the EOC/reset events.

The EOC current level IMIN is programmable with the

the trickle charge starts and rises to HIGH at an EOC event.

After the EOC is reached, the CHG status is latched at HI.

The CHG status will be reset to logic LO when the VBAT

voltage drops to below the recharge threshold (4.05V), as

shown in Figure 1.

A thermal foldback function reduces the charge current

anytime when the die temperature reaches typically +115°C.

This function guarantees safe operation when the

printed-circuit board (PCB) is not capable of dissipating the

heat generated by the linear charger.

ISL9301

VIN

VBAT

VOUT

IREF

IMIN

CHG

TIME

TO SYS

INPUT

PPR

GND

BATON

TO

μP

PRESS AND HOLD 2s TO TURN ON

BATT

PART

DESCRIPTION

10µF X5R ceramic cap

1µF X5R ceramic cap

C3

4.7µF X5R ceramic cap

1

Ω, 5% resistor

26.7k

Ω, 1%, for 150mA charge current

137k

Ω, 1%, for 23mA EOC current

1M

Ω, 1% resistor for 75µs clock period

470

Ω, 5% resistor

LEDs for indication

ISL9301