ISL9219

FN6606 Rev 2.00

Page 9 of 12

April 7, 2010

Charge Current Thermal Foldback

Overheating is always a major concern in a linear charger.

The maximum power dissipation usually occurs at the

beginning of a charge cycle when the battery voltage is at its

minimum but the charge current is at its maximum. The

charge current thermal foldback function in the ISL9219

eliminates the overheating problem.

The thermal foldback function has no impact on the charge

current until the internal temperature reaches approximately

+125°C; then charge current is reduced at a rate of

100mA/°C. For a charger with the constant charge current

set at 1A, the charge current is reduced to zero when the

internal temperature rises to +135°C.

OVP Protection

The ISL9219 is capable for up to 28V at the input pin.

However, reliability reason, the charger will stop charging

should the input voltage exceed 6V. This feature prevents

excessive heating generated by the high input voltages. If an

OVP condition is encountered, the PG pin will turn to high

impedance to indicate the OVP condition, the changer

enters the suspend state and the ACFLT turns to high

impedance. If VIN is within the power good range, the PG

pin is connected to VIN pin internally to provide a 20mA

supply current to the down stream circuit.

NTC Thermistor

The ISL9219 provides a TS pin to monitor the battery

temperature to ensure a safe charging temperature range.

The temperature range is programmable with an external

negative temperature coefficient (NTC) thermistor. The

TEMP pin is also used to detect the removal of the battery.

The ISL9219 uses two comparators (CP2 and CP3) to form a

window comparator, as shown in Figure 2. When the TS pin

condition. When the temperature returns to the set range, the

charger re-starts a charge cycle. The two MOSFETs, Q1 and

Q2, produce hysteresis for both upper and lower thresholds.

The temperature window is shown in Figure 1 for a 0°C to

+50°C typical application using a Mitsubishi type

TH11-4H104F thermistor.

Battery Removal Detection

The ISL9219 assumes that the thermistor is co-packed with

the battery and is removed together with the battery. When

the charger senses a TS pin voltage that is 2.25V or higher,

it assumes that the battery is removed. The battery removal

detection circuit is also shown in Figure 2. When a battery is

removed, the ISL9219 enters the suspend state and the

charging is halted. When a battery is inserted again, a new

charge cycle starts.

Shutdown and Suspend State

The ISL9219 can be orderly shutdown by one of these

conditions:

1. EN pin is pulled to logic HI

2. The battery has been removed from the charger. The

battery removal condition can be detected by the TS pin

(see “Battery Removal Detection” on page 9).

When shut down, the charger stays in the suspend state and

draws typically less than 300µA current from the input

power.

Under an OVP condition, the charger also enters the

suspend state.

0V

UNDER

TEMP

OVER

TEMP

TS PIN

VOLTAGE

FIGURE 1. THRESHOLD VOLTAGES FOR 0°C to +50°C

WINDOW

+

-

+

-

TS

GND

2.8V

R2

R3

R4

R5

Q1

Q2

CP2

CP3

UNDER

TEMP

OVER

TEMP

TS FUNCTION

TO TS PIN

+

-

R1

BATTERY

REMOVAL

CP1

5

A

FIGURE 2. INTERNAL CIRCUIT FOR NTC INTERFACE