10

FN9173.4

March 9, 2006

Theory of Operation

The ISL6298 is an integrated charger optimized for low-

capacity single-cell Li-ion or Li-polymer batteries. It charges

a battery with the constant current (CC) and constant voltage

(CV) profile. The charge current is trimmed to have better

than 10% accuracy at 250mA and is programmable up to

450mA. The charge voltage has 1% accuracy.

Figure 20 shows the typical operating waveforms after

pin starts to output a 2.8V supply. This supply also powers

the internal control circuit. The POR initiates a charge cycle.

Six different ways can initiate a charge cycle, as listed in

Table 1.

battery for an excessively long time. At the end of the fast

must reach an end-of-charge (EOC) condition before the

termination; otherwise, the charger issues a fault indication

through the FAULT pin. The charger issues a logic low signal

at the STATUS pin at the beginning of a charge cycle. When

the EOC condition is reached, the STATUS rises to high, as

After termination, if the battery voltage drops below a

take place. The total time for the recharge cycle is the total

negligible in a recharge cycle. More detailed description for

the operation is given below.

Power on Reset (POR)

The ISL6298 resets itself as the input voltage rises above

the POR rising threshold. The V2P8 pin outputs a 2.8V

voltage, the internal oscillator starts to oscillate, the internal

timer is reset, and the charger begins to charge the battery.

The two indication pins, STATUS and FAULT, indicate a

LOW and a HIGH logic signal respectively. Figure 20

The ISL6298 has a typical rising POR threshold of 3.4V and

a falling POR threshold of 2.4V. The 2.4V falling threshold

guarantees charger operation with a current-limited adapter

to minimize the thermal dissipation. See more details on

using a current-limited adapter in the ISL6292 datasheet,

available at http://www.intersil.com.

Internal Oscillator

The internal oscillator (see the Block Diagram) establishes a

timing reference. The oscillation period is programmable

Applications. The oscillator charges the timing capacitor to

1.5V and then discharges it to 0.5V in one period, both with

10

(EQ. 1)

A 1nF capacitor results in a 0.2ms oscillation period.

Total Fast Charge Time

The total fast charge time TIMEOUT is also programmed by

oscillation period to set the TIMEOUT, thus,

(EQ. 2)

A 1nF capacitor leads to 14 minutes of TIMEOUT. If a user

needs to set the TIMEOUT to 3.5 hours, a 15nF capacitor is

required. The charger must reach EOC before the charger

terminates, otherwise, a TIMEOUT fault will be issued.

Trickle Charge Time

The trickle charge time is limited to 1/8 of TIMEOUT. If the

fault will be issued. The end of trickle charger is determined

by the battery voltage staying above the trickle charge

threshold (given in the Electrical Specification) for 15

TABLE 1. EVENTS THAT LEADS TO A NEW CHARGE CYCLE

#

EVENT

1

Power on Reset

2

The VIN pin voltage drops below the VBAT pin voltage and

then rises back above the VBAT pin voltage

3

A new battery being inserted (detected by TEMP pin)

4

The battery voltage drops below a recharge threshold after

completing a charge cycle

5

recovery from a battery over-temperature fault

6

the EN pin is toggled from GND to floating

FIGURE 20. TYPICAL OPERATING WAVEFORMS

VIN

V2P8

STATUS

FAULT

VBAT

I

CHARGE

15 Cycles to

1/8 TIMEOUT

15 Cycles

POR Threshold

2.8V V

MIN

V

RECHRG

t

0

t

t

3

t

4

t

5

t

t

8

Charge Cycle

Charge Cycle

I

MIN

0.2 10

TIME

⋅

⋅

=

onds

sec

()

TIMEOUT

2

OSC

14

1nF

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

⋅

=

⋅

=

minutes

()

ISL6298