9

FN9215.1

March 20, 2007

threshold is reached, all counters are reset to zero, the

charge state machine is reset, the V2P9 pin outputs 2.9V,

the open-drain MOSFET on the DT pin is turned on, and the

ambient temperature monitoring circuit starts to function.

EN Pin

If all other charge conditions are met, pulling the EN pin low

starts the ISL6297 charge operation. In a typical application,

EN connects to the ID pin of a battery pack. Inside the

battery pack the ID pin connects to ground through a

resistance of less than 27k

Ω. When the battery is not

attached to the charger, the ISL6297 internally pulls the EN

pin high to disable the charger. An RC filter on the ISL6297

EN input improves the charger ESD protection.

Table 1 summarizes the status of each pin when the EN pin

disables the IC.

Plug-in Indication

POR threshold, the LEDs provide a Plug-in Indication

sequence. First the RED LED turns on for 500ms, then the

GREEN LED turns on for 500ms, then both turn on for

500ms (giving a YELLOW indication), and finally all the

LEDs turn off.

The ISL6297 turns on an LED by pulling the output line LOW

with a constant current of 10mA (typical). A typical bi-color

LED needs no series resistor for the LED connection,

however, current can be minimized by adding a serial

resistor in each LED path.

Idle Condition and Battery Connection

temperature is within the allowed range the ISL6297 is ready

to start the charge operation. Charging is initiated by

plugging in the battery, which pulls the EN pin low.

Connection Verification

The EN pin going low starts a 500ms delay. After the delay,

the ISL6297 turns on the charger for 70ms with a trickle

connected, the VSEN voltage will go up to approximately

VIN. If no battery is detected after the 70ms period, the

ISL6297 terminates the charge operation, turns off the

output voltage, and sets the LEDs off. The device remains in

this state until the EN pin is toggled or the device goes

through a power cycle. (See Figure 5.)

If the battery is connected within the 70ms open battery

detect period, the voltage on VSEN pin needs to drop below

the (falling) threshold of about 4.3V before the end of the

70ms period. If not, then the battery has not been properly

connected and an open battery connection fault condition

exists, requiring a power cycle or a toggle of EN.

After the 500ms delay, if a battery is connected, the VSEN

voltage will remain below the 4.4V threshold and the

ISL6297 assumes that the battery is connected. The device

turns on the Red LED to indicate a charge operation and

starts a short circuit detection. (See Figure 4.)

If the battery positive terminal comes loose and reconnects

after this time, the charge operation sequence continues, but

the LED indicates an end of charge condition, regardless of

the state of charge.

Short Circuit Detection

To detect a short circuit condition the ISL6297 forces the

trickle charge current to the battery. If, after 384 cycles, the

battery voltage is below 1V, the ISL6297 considers the

battery or connection to be short-circuited. In this condition,

the charger turns off and a flashing yellow indicator displays

the occurance of this “non-temperture” fault.

To clear a short circuit fault condition requires that the enable

pin be toggled, by removing the battery pack, or by cycling

the power on the charger.

Trickle Charge

If there is no short circuit the voltage is higher than 1V and

the charge operation continues with a trickle charge. In the

trickle charge, the ISL6297 applies 10% of the programmed

current to the battery. If the voltage on the cell is greater than

2.8V after 15 clock cycles, then the ISL6297 applies the full

constant current charge to the cell. However, if the voltage

on the cell does not rise above 2.8V in one eighth (1/8) of the

TIMEOUT period, then a non-temperature fault occurs and

the charger is turned off. A flashing yellow indicator

announces this condition.

TABLE 1. 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.

ISL6297