8

© 2005 Semtech Corp.

www.semtech.com

SC802/SC802A

POWER MANAGEMENT

Prelimi-

nary

Charge Timer

The timer on the SC802 is used as protection in the case

of a faulty battery and to maximize charging capacity. Tie

the RTIM pin to VCC to select the internal timer, GND to

disable the timer. Connecting a resistor between RTIM

and GND will program the total charge time according to

the following equation with the charge time expressed in

hours.

Ω

×

=

12.5k

Time

Q

Total

RTIM

The timer is programmable over the range of 2 to 6hrs.

The internal timer selection results in a charge time of

3hrs. The CHRGB blink rate in fault condtions is a func-

tion of the timer setting when an external RTIM is used.

The SC802 will automatically turn off the output when

the charge timer times out.

LDO Mode

The SC802 is designed to work with or without a battery.

If the battery is not in place the device can enter the

LDO mode. In this mode the SC802 will act like a low

dropout regulator. The output voltage is set to 4.1V, 4.2V

or externally set by a resistor divider. See the section

titled “Configuring the output voltage to the battery” for

setting an output voltage. The input pin BIPB (Battery In

Place Bar) is used to switch the SC802 from charger

mode to LDO mode. If this pin is logic high the device will

be in LDO mode, if it is logic low it will be in the charger

mode. During LDO mode the device will regulate the out-

put voltage with a current limit set by the resistor tied to

the IPRGM pin. The BIPB pin should never be left float-

ing. It should be tied through pull-up/pull-down resistors

when connected to a high impedance control pin or it

can be connected directly to the VCC pin or GND.

EN-NTC Interface

The Enable pin on the SC802 provides two functions. It

can be used to turn on/off the device by driving it to

VCC/Ground. It can also be connected to an external

resistor divider consisting of a resistor and an NTC Ther-

mistor to disable the charge cycle when the temperature

is out of range. This configuration is shown in the typical

application schematic on page 1 of the datasheet. When

the NTC voltage from the divider is above or below the

hot and cold temperature threshold values the SC802

will suspend the charge cycle by turning off the output,

freezing the charge timer, and indicating a fault on the

CHRGB LED. Hysteresis is included for both thresholds

to avoid chatter at the NTC trip points. When the tem-

Applications Information Cont.

Termination Current

Once the battery reaches the program voltage of 4.1V,

4.2V or externally set voltage, the device will transition

from a constant current source to a constant voltage

source. The current through the battery begins to de-

crease while the voltage remains constan until it falls

below the programmed termination current set by the

termination resistor on the ITERM pin. The SC802 will

turn off the CHRGB Led. If the timer is enabled the out-

put will continue to float charge in CV mode until the

timer expires. If the timer is disabled than the output will

turn off as soon as the termination current level is

reached. The equation for setting the the termination

current

The termination current is programmable up to 67mA

for the SC802. The termination current is programmable

up to 150mA with VCC=5V on the SC802A.

Monitor Mode

When a charge cycle is completed, the SC802 output

turns off and the device enters monitor mode. If the

voltage of the battery falls below the recharge threshold

of CV-100mV the charger will clear the charge timer and

re-initiate a charge cycle. The maximum current drain of

the battery during monitor mode will be no more than

1uA over temperature. The status of the charger output

as a function of BIPB, Timer, and IOUT is shown below.

t

u

p

t

u

O

e

t

a

t

S

B

P

I

Br

e

m

i

Tt

u

o

I

n

O

h

g

i

HA

/

NA

/

N

n

O

w

o

Lr

e

m

i

T

<

TA

/

N

f

f

O

w

o

Lr

e

m

i

T

>

TA

/

N

f

f

O

w

o

Ld

e

l

b

a

s

i

Dn

o

it

a

n

i

m

r

e

tI

<

88

R

1.5

ITERM

:

SC802

TERM

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=

97

R

1.5

ITERM

:

SC802A

TERM

×

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

=