10

FN9252.1

May 16, 2007

During the constant voltage phase, the charge current

reduces gradually as the cell voltage rises.

Charge Termination and Recharge

As the charge current reaches the EOC (end-of-charge)

current threshold during the constant voltage phase, the

STATUS pin open-drain FET is turned off to indicate an EOC

condition. The EOC current is programmable for the

ISL9205 by connecting a resistor from the IMIN pin to GND.

For others, the EOC current is fixed at 10% of the

programmed constant charge current. If the timeout function

is available and enabled, the charger will be terminated

when the user programmed charge time limit has been

reached. If the timeout function is disabled by the TOEN pin

(ISL9205), or not available (ISL9205A), the charger will

continue to charge until the EN pin is pulled to logic LOW or

the input power has been removed. Should the charge be

terminated by the timeout function, recharge will occur when

the battery voltage falls to 150mV below the constant voltage

value. The STATUS open-drain FET is turned on when a

recharge condition is met, whether the charger is previously

terminated or not. An internal delay is implemented at the

STATUS pin for both EOC and recharge conditions to

prevent nuisance trips due to noise and fast load current

transitions. The delay time is approximately one clock cycle

(varies between 0.5 and 1.5 clock) of the internal oscillator,

which is programmed by the timer capacitor. The typical

charge waveforms in Figure 13 show the complete cycle

operation.

Temperature Monitoring and Thermal Foldback

In the event where the die temperature reaches the thermal

foldback threshold (+110°C typical), the charge current is

reduced accordingly to prevent further temperature rise. In

the ISL9205 and ISL9205D versions, there is an external

temperature monitoring function. A negative temperature

coefficient (NTC) thermistor can be connected between the

TEMP pin and GND to monitor the battery temperature or

ambient temperature. The hysteresis comparators internal to

the ISL9205 provide a valid temperature window centered at

the voltage of the TEMP pin, which is programmed by the

NTC and the pull-up resistor connected to the pin. When the

measured temperature is outside this window, the charger is

paused (both the charger and the timer are stopped) and a

fault indication is issued. If the thermistor is attached to the

battery, the TEMP function can be used to discover a battery

removal condition when the TEMP pin voltage is much

higher than the reference threshold.

POR

The power-on reset (POR) function monitors the supply

voltage. The POR has a rising edge threshold of 3.6V typical

and 2.5V typical for falling edge. The charger is expected to

operate when the input voltage is above the POR threshold.

After POR the charger will continue to operate for supply

voltage down to 2.5V typical. It is also required that the

supply voltage be higher than the VBAT pin voltage by a

typical 80mV for the charger to function.

Oscillator, TIMEOUT, and Charge Cycle

The ISL9205 incorporates with an oscillation circuit using an

external timing capacitor connected to the TIME pin. The

oscillator sets the limit for the maximum charge time during

the trickle mode and the fast mode (CC and CV). The

maximum charge time (TIMEOUT) for the fast mode is set

by:

for the trickle charge is 1/8 of the fast mode time limit. In the

ISL9205, the time-out function can be disabled by pulling the

TOEN pin to logic LOW. When TIMEOUT is disabled, the

charger will never be turned off after the EOC but will

indicate the EOC condition through the STATUS pin. For the

ISL9205B and the ISL9105D, the timeout function is always

enforced. For the ISL9105A, there is not timeout function.

A charge cycle is the time interval between the time when

the charger is enabled to the moment it is disabled. If the

battery voltage is lower than the trickle charge threshold at

the time the charger is enabled, the charger enters the trickle

mode and the timer is reset and its limit is set to 1/8 of

TIMEOUT. If the timeout function is enabled, the charger will

stop and indicate a TIMEOUT fault if the charge time is

longer than the limit. If the trickle mode completes

successfully before the time limit, the charger moves to CC

mode and the timer is reset and the time limit is set to

TIMEOUT. The charger needs to reach the EOC conditions

before the TIMEOUT interval elapsed, otherwise, a

TIMEOUT fault will be issued. The charger indicates the

EOC with the STATUS pin but does not terminate until the

TIMEOUT interval elapsed.

Disabling TIMEOUT with TOEN

In the ISL9205, the time-out function in fast charge state

(CC/CV) can be disabled by pulling the TOEN pin to logic

IREF

TRICKLE

CC

CV

4.2V

TIME

2.8V

CHG

CHARGE

CURRENT

CHARGE

VOLTAGE

STATUS

INDICATION

10%

TIMEOUT

1/8 OF

TIMEOUT

IREF

FIGURE 13. TYPICAL CHARGE CYCLE WITH TIMEOUT

ISL9205