SC802 datasheet(7/16 Pages) SEMTECH

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SC802/SC802A

POWER MANAGEMENT

PRELIMINARY

ceeds 1/4 of the total charge cycle the charger will turn

off due to a pre-charge fault. This fault is cleared when

EN or VCC is toggled or the output voltage rises above

2.8V.

Fast-Charge Mode (CC)

The fast-charge or CC mode is active when the battery

voltage is above 2.8V and less than the CV or final float

charge voltage of the battery. The fast-charge current

can be set to a maximum of 1.0A and is selected by the

program resistor on the IPRGM pin. The voltage on this

pin will represent the current through the battery enabling

a microprocessor via an analog-to-digital converter (ADC)

to monitor battery current by sensing the voltage on the

IPRGM pin. The equation to set the fast-charge current

is given by:

Note that for a given program resistor the current through

the battery in CV mode can be determined by replacing

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

equation. The CC current can also be modified by apply-

ing an analog voltage to the AFC pin as described below.

Analog Fast Charge (AFC Pin)

Many applications require more than one current setting

for Fast Charge. This feature is included in the SC802

by using the AFC function. When the AFC pin is con-

nected to VCC the device behaves as described in the

previous section. When the AFC pin is driven by and

analog voltage between 0 and 1.5V the SC802 auto-

matically uses this pin voltage to set the maximum fast-

charge current setting according to the following equa-

tion.

General Operation

The SC802 is configured based on the application for

Fast Charge and Termination current, output voltage, tim-

ing requirements, and operation with and without a bat-

tery (ldo mode). A typical charging cycle is described be-

low. Details on alternate applications and output pro-

grammability are covered in the individual sections.

The charging cycle begins when the adapter is plugged

in. The SC802 performs glitch filtering on the VCC input

and initiates a charge cycle when VCC > UVLO. At this

time, the CPB and CHRGB signals are active turning on

the charger LED’s. If the battery voltage is less than

2.8V, the SC802 will charge the output with the pre-

charge current. When the battery voltage exceeds 2.8V,

the SC802 enters fast-charge or constant current (CC)

mode. When the battery voltage reaches its final value,

the charger enters the constant voltage (CV) mode. In

this mode the output current decreases as the battery

continues to charge until the termination current level is

reached.

The CHRGB led turns off when Iout is less than

Itermination but the SC802 continues to hold the bat-

tery in CV charge mode until the timer expires. At this

point the charger enters the monitor mode where the

output remains off until Vout drops by 100mV and a new

charge cycle is initiated.

Pre-Charge Mode

Pre-charge mode is automatically enabled whenever the

battery voltage is below 2.8V. It is used to limit the power

dissipation and precondition the battery for fast charg-

ing. The pre-charge current value is selected by the re-

sistor on the ITERM pin. The pre-charge current is pro-

grammable from 10mA to 125mA on the SC802 and up

to 150mA on the SC802A. The equation to select the

pre-charge current is different for the two part types and

given by:

If the charge timer is in use there is also a maximum

allowed pre-charge duration. If the pre-charge time ex-

Applications Information

1000

1.5

FCI

SC802

PRGM

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

Iterm

0.3

1000

1.5

FCI

SC802A

PRGM

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

2.8

PCI

SC802

TERM

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

1.5

PCI

SC802A

TERM

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

1000

AFCI

SC802

PROG

AFC

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

Iterm

0.3

1000

AFCI

SC802A

PROG

AFC

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

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