9

FN9133.2

July 22, 2005

ISL6292C, the EOC current is internally set to 1/10 of the CC

charge current, that is,

(EQ. 6)

At the EOC, the STATUS signal rises to HIGH and is latched.

The latch is not reset until a recharge cycle or a new charge

cycle starts.

Charge Current Thermal Foldback

Over-heating is always a concern in a linear charger. The

maximum power dissipation usually occurs at the beginning

of a charge cycle when the battery voltage is at its minimum

but the charge current is at its maximum. The charge current

thermal foldback function in the ISL6292C frees users from

the over-heating concern.

Figure 7 shows the current signals at the summing node of

rises at a rate of 1

rate. As a mirrored current, the charge current is 100,000

times that of the sensed current and reduces at a rate of

100mA/°C. For a charger with the constant charge current

set at 1A, the charge current is reduced to zero when the

internal temperature rises to 110°C. The actual charge

current settles between 100°C to 110°C.

because of the thermal foldback. For some extreme cases if

that does happen, the charger does not indicate end-of-

charge unless the battery voltage is already above the

recharge threshold.

2.8V Bias Voltage

The ISL6292C provides a 2.8V voltage for biasing the

internal control and logic circuit. This voltage is also

available for external circuits such as the NTC thermistor

circuit. The maximum allowed external load is 2mA.

Indications

The ISL6292C has three indications: the input presence, the

charge status, and the fault indication. The input presence is

indicated by the V2P8 pin while the other two indications are

presented by the STATUS pin and FAULT pin respectively.

Figure 8 shows the V2P8 pin voltage vs. the input voltage.

Table 2 summarizes the other two pins.

Shutdown

The ISL6292C can be shutdown by pulling the EN pin to

ground. When shut down, the charger draws typically less

than 30

µA current from the input power and the 2.8V output

at the V2P8 pin is also turned off. The EN pin needs be

driven with an open-drain or open-collector logic output, so

that the EN pin is floating when the charger is enabled. If the

EN pin is driven by an external source, the POR threshold

voltage will be affected.

Input and Output Capacitor Selection

Typically any type of capacitors can be used for the input

and the output. Use of a 0.47

µF or higher value ceramic

capacitor for the input is recommended. When the battery is

attached to the charger, the output capacitor can be any

ceramic type with the value higher than 0.1

µF. However, if

there is a chance the charger will be used as an LDO linear

regulator, a 10

µF tantalum capacitor is recommended.

1

10

⋅

=

FIGURE 7. CURRENT SIGNALS AT THE AMPLIFIER CA INPUT.

TEMPERATURE

I

R

I

T

I

SEN

TABLE 2. STATUS INDICATIONS

FAULT STATUS

INDICATION

High

High

Charge completed with no fault (Inhibit) or

Standby

High

Low

Charging in one of the three modes

Low

High

Fault

NOTE: Both outputs are pulled up with external resistors.

FIGURE 8. THE V2P8 PIN OUTPUT vs THE INPUT VOLTAGE

AT THE VIN PIN. VERTICAL: 1V/DIV,

HORIZONTAL: 100ms/DIV

3.4V

2.4V

2.8V

V

IN

V2P8

ISL6292C