8

FN9139 .1

April 19, 2005

Applications Information

Power-On Reset (POR)

The ISL6292B has a 3.4V rising POR threshold. Before the

input voltage reaches the POR threshold, the 2.9V V2P9 pin

outputs 0V and the charger is disabled. Once the POR

threshold is reached, 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. After a

delay and after the input voltage rises above the battery

voltage, the charger control circuit starts to work and the DT

pin impedance becomes high. Figure 3 shows the sequence

of the events at power on. The POR has a falling threshold

of 2.4V typically. At power on, all counters are reset to zero.

When the ISL6292B is used as a traditional linear charger,

with a current-limited supply, the CC current is determined

following equation:

(EQ. 1)

The trickle charge current is 10% of IREF, that is,

(EQ. 2)

The ISL6292B has a comparator with 100mV offset voltage

to ensure the input voltage is higher than the battery voltage

before charging starts (see the Block Diagram). This

The EOC current is programmed by the IMIN pin and can be

calculated by the following equation:

(EQ. 3)

The EOC current has a programming range up to 400mA.

To qualify as an EOC condition, the charge current needs to

more than three to four cycles of the internal oscillator;

additionally, the battery voltage rises above the recharge

threshold given in the Electrical Specification table.

Internal Oscillator

The internal oscillator establishes a timing reference. The

oscillation period is programmable with an external timing

oscillator charges the timing capacitor to 1.5V and then

discharges it to 0.5V in one period, both with 10

µA current.

(EQ. 4)

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

accuracy of the period is mainly dependent on the accuracy

of the capacitance and the internal current source.

The total charge time for the CC mode and CV mode is

limited to a length of TIMEOUT, which can be found by:

(EQ. 5)

FIGURE 3. EVENT SEQUENCE AT POWER UP

VIN

V2P9

DT

Imped

Charger

Start

POR

0.8V

----------------- 10

5

×

A

()

=

0.8V

----------------- 10

4

×

A

()

=

0.8V

---------------- 10

4

×

A

()

=

0.2 10

TIME

⋅

⋅

=

onds

sec

()

FIGURE 4. OPERATION WAVEFORMS

VIN

V2P9

RED

GRN

VBAT

I CHG

15 Cycle s to

1/8 TIM EOUT

15

Cycle s

POR

Thre shold

t0 t1 t2 t3

t4

t5

t6 t7

t8

Charge

Cycle

Charge

Cycle

IMIN

DT

Impe d.

MIN

MIN

MIN

RECHRG

V

2.8V V MIN

TIMEOUT

14

1nF

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

⋅

=

minutes

()

ISL6292B