7

FN9241.0

October 4, 2005

Theory of Operation

The ISL9200 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 over-

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

ISL9200 protects up to 30V input voltage.

Power-Up

The ISL9200 has a power-on reset (POR) threshold of 2.6V

with a built-in hysteresis of 100mV. 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 inrush 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 (Figure 1). CP1 has an accurate reference of

1.2V from the bandgap reference. The OVP threshold is set

by the resistive divider consisting of R1 and R2. The

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

3V

4.3V

5V

6.5V

TEMPERATURE (°C)

ISL9200