© 2008 Semtech Corporation

SC802/SC802A

13

the VPRGM pin with the divider tap connected to the BSEN

pin to utilize this feature. The Adjust Mode CV regulation

voltage is set by the following equation.

0

.

3

R

R

1

V

LO

ADJ

HI

ADJ

ADJ

CV

To ensure detection of V

CV

Adjust Mode, R

ADJ–HI

should be

at least 130kΩ. The capacitor across R

ADJ–HI

in the feedback

network provides zero-pole frequency compensation for

stability. Place the zero according to the following equa-

tion to ensure stability.

kHz

100

2

1

C

R

ADJ

HI

ADJ

In V

CV

Adjust Mode, V

CV–ADJ

must satisfy V

VCC

> V

CV–ADJ

+

150mV to ensure regulation. If V

VCC

approaches V

CV–ADJ

,

V

CV–ADJ

will drop out such that V

CV–ADJ

will be approximately

V

VCC

– 150mV.

LDO Mode

The SC802/A can operate with or without a battery. If the

battery is not in place the device can enter LDO Mode.

The input pin BIPB is used to switch the SC802/A from

charger mode to LDO mode. If this pin is driven logic high

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

the charger mode. The BIPB pin should never be left float-

ing. It should be tied through pull-up or pull-down resis-

tors when connected to a high impedance control pin or

it can be connected directly to the VCC pin or GND.

In LDO Mode the SC802/A will function as a low dropout

voltage regulator. The EN_NTC pin functions remain

active, and the status indicators are active, including the

CHRGB indicator. The timer is inactive. The output remains

enabled even when I

VOUT

< I

TERM

. The output voltage can be

set to 4.1V, 4.2V or externally set by a resistor divider, with

a current limit equal to I

FQ

. The pre-charge threshold is

ignored.

Remote Kelvin Sensing at the Battery

Kelvin sensing of both the positive and negative terminals

of the battery is available on the SC802/A. The BSEN pin

provides the positive sensing voltage feedback to the CV

amplifier and should be connected as close to the battery

positive terminal as possible. The REFGND pin should be

Kelvin connected to the negative terminal of the battery.

This provides maximum flexibility in PCB layout. This also

results in a greater accuracy in sensing the battery voltage

at the battery terminals. When laying out the PCB the

designer should route the BSEN pin directly to the battery

terminal connections. (For Adjust Mode, the high-side

resistor should be connected directly to the battery termi-

nal connections.) In LDO mode, as in Charging mode, the

BSEN pin must sense the output voltage, so BSEN should

never be left unconnected.

Over-Current and Max Temperature Protection

Over-current protection is inherent in all modes of opera-

tion. When the device is in charge-mode (BIPB=low) the

output is current limited to either the pre-charge current

limit value or the fast-charge current limit value depend-

ing on V

VOUT

. When the device is in LDO mode (BIPB =

high) the output current is limited to the fast-charge

current limit. Maximum die temperature protection is

provided on the SC802/A. This feature allows the SC802/A

to operate with maximum power dissipation by disabling

the output current when the die temperature reaches the

over temperature limit. The device will then operate as a

pulse charger in extreme power dissipation applications,

delivering the maximum allowable output current while

regulating the internal die temperature to a safe level.

Capacitor Selection

Low cost, low ESR ceramic capacitors such as the X5R and

X7R dielectric material types are recommended. The

VOUT pin capacitance range is typically 1μF to 4.7μF, but

C

VOUT

can be as large as desired to accommodate the

required input capacitors of regulators connected directly

to the battery terminal. The VCC pin input capacitor C

VCC

is typically between 0.1μF to 1μF, but larger values will not

degrade performance. Capacitance must be evaluated at

the expected bias voltage (V

CV

for C

VOUT

, the expected VCC

supply regulation voltage for C

VCC

), rather than the zero-

volt capacitance rating.

Applications Information (continued)