SC802AEVB datasheet(10/18 Pages) SEMTECH

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SC802/SC802A

Applications Information (continued)

on the IPRGM pin. The fast-charge current is given by the

following equations.

1000

IPRGM

(SC802)

TERM

IPRGM

1000

(SC802A)

Note that for a given program resistor the current through

the battery in CV regulation can be determined by replac-

ing 1.5 with the actual voltage on the IPRGM pin in the

equations. In the case of the SC802A, the I

TERM

term

applies only prior to termination (while CHRGB is low),

and should be excluded following termination. The CC

current can also be modified by applying an analog

voltage to the AFC pin as described in the next section.

Analog Fast-Charge

Many applications require more than one current setting

for fast-charge. This feature is included in the SC802/A by

using the AFC function. When the AFC pin is connected

to VCC the SC802/A operates as described in the previous

section. When the AFC pin is driven by an analog voltage

between 0 and 1.5V the SC802/A automatically uses this

pin voltage to set the maximum fast-charge current

setting according to the following equation.

1000

IPRGM

AFC

AFQ

(SC802)

TERM

IPRGM

AFC

AFQ

1000

(SC802A)

Monitor State

When a charge cycle is completed, the SC802/A output

turns off and the device enters monitor state. If the

voltage of the battery falls below the re-charge voltage of

− VT

ReQ

, nominally 100mV below V

, the charger will

clear the charge timer and re-initiate a charge cycle. The

maximum current drain from the battery during monitor

state is less than 1μA over temperature. The status of the

charger output as a function of BIPB, timer status, and

VOUT

in the following table.

Output

State

BIPB

Timer

VOUT

High

N/A

Low

t < T

QCOMP

N/A

Off

Low

t > T

QCOMP

N/A

Off

Low

Disabled

< I

TERM

Charge Timer

The timer in the SC802/A provides protection in the event

of a faulty battery, and maximizes charging capacity.

Connect the RTIME pin to VCC to select the internally

programmed timer, and to GND to disable the timer.

Connecting a resistor between the RTIME pin and GND

will program the total charge complete time T

QCOMP

according to the following equation.

RTIME

(kΩ) = T

QCOMP

(hours) x 12.5 (kΩ/hour)

The timer is programmable over the range of two to six

hours. The internal timer selection provides a charge time

of three hours. The SC802/A automatically turns off the

output when the charge timer times out, and then enters

the Monitor State. A re-charge cycle resets and restarts

the timer.

Note that the CHRGB fault indication blink rate is a func-

tion of the timer setting, whether externally programmed

or set internally. When the timer is disabled, the blink rate

is the same as if the timer were internally set.

EN_NTC Interface

The EN_NTC pin is the interface to a battery pack temper-

ature sensing Negative Temperature Coefficient (NTC)

thermistor. It can be used to suspend charging if the

battery pack temperature is outside of a safe-to-charge

range. The EN_NTC interface also serves as a charger

disable or NTC–unconditional enable input.

The recommended EN_NTC network is a fixed-value

pullup resistor (designated R

NPU

) from the EN_NTC pin to

the VCC pins, and the battery pack NTC thermistor (desig-

nated R

NTC

) from the EN_NTC pin to ground. In this con-

figuration, shown in the Typical Application Circuit on

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