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FN9139 .1

April 19, 2005

create a hysteresis for each comparator respectively. The

DT pin is shorted to GND via the internal Q3 MOSFET when

the charger is not charging, resulting in the equivalent circuit

shown in Figure 7 (A). The on-resistance of Q3 is typically

50

Ω and is negligible compared to the external resistors.

When the charger starts to charge, Q3 is turned off to set a

higher temperature range determined by the external

The DT pin allows the user to set up a higher shut down

ambient temperature after the charger starts up.

follows the following equation:

shows the temperature windows before, during, and after

charging. Before and after charging, the temperature window

is -5°C to 45°C with 5°C hysteresis. During charging, the

high temperature limit changes to 45°C +

∆T. If this limit is

exceeded, the charger is stopped and the temperature has

to come back to below 40°C for the charging to be allowed

again. The low temperature limit is also increased. However,

at low temperature, therefore, the influence on the

temperature threshold is not as much as at high

temperature. Typically, the low temperature threshold is

raised by less than 2°C, as shown in Figure 8.

Charge Current Thermal Foldback

The thermal foldback function monitors the die temperature

and reduces the charge current when the die temperature

rises above 100°C to prevent further temperature rise. The

charge current reduces at a rate of 100mA/°C after

exceeding 100°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 110°C. The actual charge

current settles between 100°C to 110°C.

because of the thermal foldback. For some extreme cases if

that does happen, the charger does not indicate end-of-

charge unless the battery voltage is already above the

recharge threshold.

2.9V Bias Voltage

The ISL6292B provides a 2.9V voltage for biasing the

internal control and logic circuit. This voltage is also

available for external circuits such as the NTC thermistor

circuit. The maximum allowed external load is 2mA.

EN Pin

The EN pin allows direct interface to the battery ID pin of a

battery pack. The battery ID pin is connected with a resistor

of a value less than 27k

Ω to ground inside the battery pack.

When the battery is not attached, the EN pin is pulled up by

an internal source to the V2P9 pin to disable the charger.

The 2.9V internal regulator is on as long as the input power

is applied, independent of the EN input. Table 2 summarizes

the status of each pin when the IC is disabled.

FIGURE 7. EQUIVALENT CIRCUITS FOR THE NTC DIVIDER

(A) BEFORE CHARGING STARTS

(B) DURING CHARGING.

V2P9

TEMP

DT

R

U

R

T

R

Q3

GND

V2P9

TEMP

R

U

R

T

R

D

GND

(A)

(B)

TABLE 2. SUMMARY OF PIN BEHAVIOR WHEN THE IC IS

DISABLED BY THE EN PIN

PIN

BEHAVIOR

V2P9

Outputs 2.9V.

RED

High impedance

GRN

High impedance

DT

Low impedance

IREF

Outputs 0.8V

IMIN

Outputs 0.8V

TEMP

The temperature monitoring circuit remains functioning.

FIGURE 8. BOARD TEMPERATURE MONITORING WHEN

THE CHARGE IS NOT CHARGING, THE

TEMPERATURE WINDOW IS -5°C AND 45°C.

ONCE THE CHARGER STARTS, THE

TEMPERATURE WINDOW IS 1.X°C TO 45°C+

∆T.

∆T

CHARGE

NOTCHARGE

NOTCHARGE

ISL6292B