11

FN9173.4

March 9, 2006

the charger stays in the trickle mode is 15 cycles. Usually for

in Figure 20). If the battery voltage falls below the trickle

charge threshold during the 15 cycles, the 15-cycle counter

is reset (not the total-trickle-charge-time counter) and the

charger remains in the trickle mode.

Disabling TIMEOUT Limit

The TOEN pin allows the user to disable the fast charge

TIMEOUT limit by pulling the TOEN pin to LOW or shorting it

to GND. When this happens, the charger never terminates.

The STATUS pin still issues the EOC indication when the

EOC condition is reached. The EOC indication is latched

and does not change until a new charge cycle starts,

initiated by the events listed in Table 1. Leaving the TOEN

pin floating is recommended to enable the TIMEOUT. Driving

the TOEN pin above 3.0V is not recommended. The trickle

charge time limit can never be disabled. For the 3x3 DFN

package option, the TOEN pin is left floating internally and,

therefore, the TIMEOUT cannot be disabled.

CC Mode Current Programming

The charge current is programmed by the IREF pin. There

are three ways to program the charge current:

1. driving the IREF pin above 1.3V

2. driving the IREF pin below 0.4V,

The voltage of IREF is regulated to a 0.8V reference voltage

when not driven by any external source. The charging

current during the CC mode is 25,000 times that of the

IREF pin is used, the charge current is,

The internal reference voltage at the IREF pin is capable of

sourcing less than 100

µA current. When pulling down the

IREF pin with a logic circuit, the logic circuit needs to be able

to sink at least 100

µA current.

The actual charge current may be affected by the thermal

foldback function. See the Thermal Foldback section for

more details.

Trickle Mode Current

The charge current in the trickle mode is 20% of the

programmed CC mode charge current, that is:

End-of-Charge (EOC) Current

starts to indicate the end of the charge with the STATUS pin,

1. By connecting a resistor between the IMIN pin and

ground,

2. Or by connecting the IMIN pin to the V2P8 pin.

equation below:

and the ground, as shown in the Typical Application Circuit.

ISL6298 in the 3x3 DFN package, the IMIN pin is connected

internally to the V2P8 pin.

EOC Conditions

The EOC indication is asserted when the following

conditions are satisfied simultaneously:

1. The battery voltage is above the recharge threshold, and

2. The charge current is lower than the EOC current.

The two conditions can prevent prematurely indicating EOC

due to thermal foldback or other transient events.

Recharge

After a charge cycle is completed, charging is prohibited until

(see Electrical Specifications). Then a new charge cycle

2.8V Voltage Regulator

The V2P8 pin is the output of an internal 2.8V linear regulator.

The 2.8V is the voltage supply for the internal control circuit

and can also be used by external circuits, such as the NTC

thermistor circuit. The external load is not recommended to

exceed 2mA. The V2P8 pin is recommended to be decoupled

with a 1

µF ceramic capacitor.

NTC Thermistor Interface

The TEMP pin offers an interface to an external NTC

thermistor. This pin has two functions: to monitor the battery

ambient temperature or to monitor the insertion of the battery.

The ISL6298 assumes that the NTC thermistor is inside the

battery pack. The battery and the NTC thermistor are inserted

or removed together. Removing the NTC thermistor disables

the charger.

Figure 21 shows the implementation of the TEMP pin. The

comparator CP1 monitors the existence of the NTC thermistor.

When the thermistor is removed, the TEMP pin voltage is

255mA

0.8V

----------------- 25000

×

A

()

100mA















=

>

<

(EQ. 3)

⋅

=

(EQ. 4)

2500

----------------

2500

0.8V

---------------- A

()

⋅

=

⋅

=

(EQ. 5)

ISL6298