SC802AEVB datasheet(9/18 Pages) SEMTECH

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SC802/SC802A

General Operation

The SC802 and SC802A can be configured independently

with respect to fast-charge and termination current,

output voltage, timing, and operation with and without a

battery (LDO mode). A typical charging cycle is described

in this section. Details on alternate applications and

output programmability are covered in subsequent sec-

tions. Wherever the SC802 and SC802A descriptions are

the same, the part will be referred to as the SC802/A.

The charging cycle begins when the adapter is plugged in.

The SC802/A performs glitch filtering on the VCC input

and initiates a charge cycle when V

VCC

> VT

UVLOR

. The CPB

and CHRGB signals turn on the charger LED’s. If the battery

voltage is less than 2.8V, the SC802/A will charge the

output with the pre-charge current. When the battery

voltage exceeds 2.8V, the SC802/A enters fast-charge or

Constant Current (CC) regulation. When the battery

voltage reaches its final value, the charger enters Constant

Voltage (CV) regulation. The CV regulation output voltage,

), can be programmed to fixed values V

CV-HI

= 4.2V,

CV-LO

= 4.1V, or programmed to any voltage V

CV-ADJ

using

the available Adjust Mode. In CV regulation the battery

accepts decreasing current until the output current (I

VOUT

)

reaches the programmed termination current, designated

TERM

When I

VOUT

< I

TERM

, an event known as charge termination,

the CHRGB status indicator turns off, but the SC802/A

continues to hold the battery in CV regulation until the

timer cycle is completed. At this point the charger enters

the monitor state where the output remains off until V

VOUT

drops by VT

ReQ

, nominally 100mV, and a new charge cycle

is initiated.

Termination Current

When the battery reaches the CV voltage (V

), the charger

transitions from a constant current source to a constant

voltage source. The current through the battery begins to

decrease while the voltage remains constant until the

current decreases below the programmed termination

current set by the ITERM pin resistance to ground. Upon

termination, the SC802/A will turn off the CHRGB status

indicator. If the timer is enabled, the output will remain in

CV regulation until the timer cycle is complete. If the timer

is disabled, then the output will turn off as soon as the

termination current level is reached. The termination

current is programmed according to the following

equations.

ITERM

TERM

(SC802)

ITERM

TERM

(SC802A)

The termination current is programmable up to 67mA for

the SC802, and up to 150mA for the SC802A.

Pre-Charge

Pre-charge regulation is automatically enabled when the

battery voltage is below the pre-charge threshold, VT

PreQ

nominally 2.8V. Pre-charge is required to precondition

the battery for fast-charging, and to limit the power dis-

sipation in the charger. The pre-charge current value, I

is determined by the ITERM pin resistance to ground. The

pre-charge current is programmable from 10mA to

125mA with the SC802, and up to 150mA with the

SC802A. The pre-charge current is given by the following

equations.

ITERM

(SC802)

ITERM

(SC802A)

If the charge timer is enabled, a pre-charge timer is also

enabled. If the pre-charge time exceeds 1/4 of the pro-

grammed total charge time, the charger will turn off and

a pre-charge fault will be indicated by blinking the CHRGB

status indicator. This fault is cleared when the charger is

disabled (by grounding the EN_NTC pin), or the VCC input

voltage is cycled, or the output voltage rises above 2.8V.

Fast-Charge

Fast-charge or CC regulation is active when the battery

voltage is above VT

PreQ

and less than V

, the final float

charge voltage of the battery. The fast-charge current

can be set to a maximum of 1.5A and is selected by the

program resistor on the IPRGM pin. The voltage on this

pin represents the current through the battery. It enables

a microprocessor via an Analog-to-Digital Converter

(ADC) to monitor battery current by sensing the voltage

Applications Information

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