LT1769IGN datasheet(6/16 Pages) LINER

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LT1769

GND (Pins 1 to 3, 7, 8, 14, 15, 22, 26 to 28): Ground Pins.

Must be connected to expanded PC lands for proper heat

sinking. See Applications Information section for details.

SW (Pin 4): 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): This pin is used to bootstrap and drive the

switch power NPN transistor to a low on-voltage for low

power dissipation. In Figure 1, VBOOST = VCC + VBAT 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): Undervoltage Lockout Input. The rising thresh-

old 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 approximately

200

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

When connected to VIN with no resistor divider, the built-

in 6.7V undervoltage lockout will be effective.

OVP (Pin 9): 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): 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): This is the negative input to the input current

limit amplifier CL1.

COMP1 (Pin 12): 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): Current Amplifier CA1 Input. Sensing can

be at either terminal of the battery.

SPIN (Pin 16): This pin is for the current amplifier CA1

bias. It must be connected to RS1 as shown in the 2A

Lithium Battery Charger (Figure 1).

BAT (Pin 17): 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.

UVOUT (Pin 19): This is an open-collector output for

undervoltage lockout status. It stays low in undervoltage

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

VCC. Note that the base drive of the open-collector NPN

comes from CLN pin. UVOUT stays low only when CLN is

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

100

µA.

VC (Pin 20): This is the inner loop control signal for the

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

operation, a higher VC corresponds to higher 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): This pin is for programming the charge

current and for system loop compensation. During normal

operation, VPROG stays close to 2.465V. If it is shorted to

GND switching will stop. When a microprocessor con-

trolled DAC is used to program charge current, it must be

capable of sinking current at a compliance up to 2.465V.

VCC1, VCC2, VCC3 (Pins 23 to 25): Input Supply. For good

bypass, a low ESR capacitor of 15

µF or higher is required,

with the lead length kept to a minimum. VCC should be

between 8V and 28V and at least 3V higher than VBAT.

Undervoltage lockout starts and switching stops when

VCC goes below 7V typical. Note that there is an internal

parasitic diode from SW pin to VCC pin. Do not force VCC

below SW by more than 0.7V with battery present. All three

VCC pins should be shorted together close to the pins.

PIN FUNCTIONS

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