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 2004 Semtech Corp.

www.semtech.com

SC806

POWER MANAGEMENT

General Operation

The SC806 is configured based on the application for

Fast Charge and Termination current. A typical charging

cycle is described below. Details on alternate applica-

tions and output programmability are covered in the indi-

vidual sections.

The charging cycle begins when the adapter is plugged

in. The SC806 performs glitch filtering on the VCC input

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

time, the CHRGB and CPB signals are active low turning

on the LEDs. If the battery voltage is less than 2.8V, the

SC806 will charge the output with the pre-charge cur-

rent. When the battery voltage exceeds 2.8V, the SC806

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 voltage is held constant and the current de-

creases until the termination current level is reached.

At this point the charger enters monitor mode and the

CHRGB output is high impedance. The charger output

remains off in monitor mode 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. The equation to se-

lect the pre-charge current is given by:

100

R

1.5

PCI

TERM

•













=

Fast-Charge Mode (CC)

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

voltage is above 2.8V and less than the 4.2V CV voltage

of the battery. The fast-charge current can be set to a

maximum of 1.0A and is selected by the program resis-

tor on the IPRGM pin. The voltage on this pin will repre-

sent the current through the battery enabling a micro-

processor to monitor battery current by sensing the volt-

age on the IPRGM pin. The equation to set the fast-

charge current is given by:

1000

PRGM

R

1.5

FCI

•

















=

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.

Termination Current

Once the battery reaches the program voltage of 4.2V

the device will transition from a constant current source

to a constant voltage source and the current through

the battery begins to decrease while the voltage remains

constant. When the current falls below the programmed

termination current set by the termination resistor on

the ITERM pin, the SC806 will transition the CHRGB pin

from low to high. The equation to set the termination

current is given by:

100

R

1.5

ITERM

TERM

•













=

Monitor Mode

When a charge cycle is completed, the SC806 output

turns off and the device enters monitor mode. If the

voltage of the battery falls below the recharge threshold

of 4.1V the charger will re-initiate a charge cycle. The

maximum current drain of the battery during monitor

mode will be no more than 1µA over temperature

NTC Input/NOBAT output

The SC806 detects the absence of the battery by moni-

toring the voltage on the NTC pin. When the NTC pin

voltage exceeds 90% of VCC the NOBAT output is driven

high. This function utilizes the standard NTC configura-

tion with the NTC component residing in the battery pack.

When the battery is removed the NTC element in the

resistor divider is missing and the NTC voltage is pulled

up to VCC.

The NOBAT output can be used to signal the system that

the battery has been removed or drive an external LED.

DIS Device Disable Interface

The DIS pin on the SC806 is used to shutdown the SC806

charger. This pin must be pulled low to enable the charger,

high will disable the charger (do not leave floating). The

CPB output indicating the adapter input status is active

regardless of the state of DIS.