6

LT1769

1769fa

GND (Pins 1 to 3, 7, 8, 14, 15, 22, 26 to 28/Pins 4, 5, 14,

20): Ground Pins. Must be connected to expanded PC

lands for proper heat sinking. See Applications Informa-

tion section for details.

SW (Pin 4/Pin 1): Switch Output. The Schottky catch

diode must be placed with very short lead length in close

proximity to SW pin and GND.

BOOST (Pin 5/Pin 2): This pin is used to bootstrap and

drive the switch power NPN transistor to a low on-voltage

when switch is on. For lowest IC power dissipation,

connect boost diode D1 to a 3V to 6V at 30mA voltage

source (see Figure 10).

UV (Pin 6/Pin 3): Undervoltage Lockout Input. The rising

threshold is at 6.7V with a hysteresis of 0.5V. Switching

stops in undervoltage lockout. When the input supply

(normally the wall adapter output) to the IC is removed, the

UV pin must be pulled down to below 0.7V (a 5k resistor

from adapter output to GND is required) otherwise the

reverse battery current drained by the IC will be approxi-

mately 200

µA instead of 3µA. Do not leave the UV pin

the built-in 6.7V undervoltage lockout will be effective.

OVP (Pin 9/Pin 6): This is the input to amplifier VA with a

threshold of 2.465V. Typical bias current is about 3nA out

of this pin. For charging lithium-ion batteries, VA monitors

the battery voltage and reduces charging when battery

voltage reaches the preset value. If it is not used, the OVP

pin should be grounded.

CLP (Pin 10/Pin 8): This is the positive input to the input

current limit amplifier CL1. The threshold is set at 100mV.

When used to limit supply current, a filter is needed to filter

out the 200kHz switching noise.

CLN (Pin 11/Pin 7): This is the negative input to the input

current limit amplifier CL1.

COMP1 (Pin 12/Pin 9): This is the compensation node for

the input current limit amplifier CL1. At input adapter

current limit, this node rises to 1V. By forcing COMP1 low

with an external transistor, amplifier CL1 will be defeated

(no adapter current limit). COMP1 can source 200

µA. If

this function is not used, the resistor and capacitor on

COMP1 pin, shown on the Figure 1 circuit, are not needed.

SENSE (Pin 13/Pin 10): Current Amplifier CA1 Input.

Sensing can be at either terminal of the battery.

SPIN (Pin 16/Pin 11): This pin is for the current amplifier

Lithium Battery Charger (Figure 1).

BAT (Pin 17/Pin 12): Current Amplifier CA1 Input.

COMP2 (Pin 18): This is also a compensation node for

amplifier CL1. Voltage on this pin rises to 2.8V at input

adapter current limit and/or at constant-voltage charging.

undervoltage lockout status. It stays low in undervoltage

state. With an external pull-up resistor, it goes high at valid

higher than 2V. Pull-up current should be kept under 100

µA.

the current mode PWM. Switching starts at 0.7V. In

charge current. A capacitor of at least 0.33

µF to GND

filters out noise and controls the rate of soft start. To stop

switching, pull this pin low. Typical output current is 30

µA.

PROG (Pin 21/Pin 16): This pin is for programming the

charge current and for system loop compensation. During

shorted to GND switching will stop. When a microproces-

sor controlled DAC is used to program charge current, it

must be capable of sinking current at a compliance up to

2.465V.

Supply. For good bypass, a low ESR capacitor of 15

µF or

higher is required, with the lead length kept to a minimum.

close to the pins.