7

FN6489.0

May 21, 2007

Theory of Operation

The ISL9209C is an integrated circuit (IC) optimized to

provide a redundant safety protection to a Li-ion battery from

charging system failures. The IC monitors the input voltage,

the battery voltage, and the charge current. When any of the

above three parameters exceeds its limit, the IC turns off an

internal P-Channel MOSFET to remove the power from the

charging system. In addition to the above protected

parameters, the IC also monitors its own internal

temperature and turns off the P-Channel MOSFET when the

temperature exceeds +140°C. Together with the battery

charger IC and the protection module in a battery pack, the

charging system has triple-level protection from

overcharging the Li-ion battery and is two-fault tolerant. The

ISL9209C protects up to 30V input voltage.

Power-up

The ISL9209C has a power-on reset (POR) threshold of

2.6V with a built-in hysteresis of 125mV. Before the input

voltage reaches the POR threshold, the internal power PFET

is off. Approximately 10ms after the input voltage exceeds

the POR threshold, the IC resets itself and begins the soft-

start. The 10ms delay allows any transients at the input

during a hot insertion of the power supply to settle down

before the IC starts to operate. The soft-start slowly turns on

the power PFET to reduce the in-rush current as well as the

input voltage drop during the transition. The power-up

behavior is illustrated in Figure 2.

Input Overvoltage Protection (OVP)

The input voltage is monitored by the comparator CP1 in the

“Block Diagram” on page 3 (Figure 1). CP1 has an accurate

reference of 1.2V from the bandgap reference. The OVP

FIGURE 20. EN INPUT THRESHOLD vs TEMPERATURE

FIGURE 21. EN PIN INTERNAL PULL-DOWN RESISTANCE

FIGURE 22. ON-RESISTANCE vs TEMPERATURE AT DIFFERENT INPUT VOLTAGES

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-50

-20

10

40

70

100

130

TEMPERATURE (°C)

150

160

170

180

190

200

210

220

230

240

250

-50

-20

10

40

70

100

130

TEMPERATURE (°C)

0

0.1

0.2

0.3

0.4

0.5

-50

-20

10

40

70

100

130

TEMPERATURE (°C)

3V

4.3V

5V

5.5V

ISL9209C