LTC1730-4/LTC1730-4.2

5

1730f

PI FU CTIO S

LTC1730ES8-4.2

SENSE (Pin 1): Maximum Overcurrent Sense Input. A

exceeds 100mV, the pass transistor immediately turns off

= 0.1

µF). The on-off cycle will continue, as long as the

overcurrent condition persists or until the timer runs out.

If overcurrent protection is not needed, short SENSE to

13.2V). Bypass this pin with a 1

µF capacitor in series with

a 4.7

GATE pin is also required. The capacitor controls the slew

current when the input voltage is first applied. When the

manner, with a slope equal to 10

µA/C. When the pass

CHRG (Pin 3): Open-Drain Charge Status Output. When a

depleted battery is being charged, the CHRG pin is pulled

to ground by an N-MOSFET capable of driving an LED.

Once the duty cycle at the GATE pin drops below 10%, the

N-MOSFET turns off and a weak 40

µA current source to

ground turns on to indicate a near end-of-charge (C/10)

condition. When a time-out occurs or the input supply is

removed, the CHRG pin goes high impedance.

GND (Pin 4): Electrical Ground Connection and provides

a thermal path from the IC to the PC board copper. Use

large copper pads and traces for maximum heat transfer.

TIMER (Pin 5): Timer Set Pin. The timer period is set by a

OFF time and the overcurrent time-out period are all set by

the same timer period.

NTC/SHDN (Pin 6): Input to the NTC (Negative Tempera-

ture Coefficient) Thermistor Monitoring and Shutdown

Circuitry. With an external 10k

ΩNTCthermistortoground

ture of the battery pack and stop charging when the

temperature is out of range. When the voltage at this pin

charge cycle is suspended and the internal timer is frozen.

The CHRG pin output status is not affected in this hold

state.

When this pin is pulled below 50mV, the IC goes into the

shutdown mode. The charging stops (the GATE pin is

pulled to ground) the timer is reset and the CHRG pin goes

into a high impedance state.

GATE (Pin 7): Gate Drive Output Pin for Internal and

External Pass Transistors. An external N-MOSFET transis-

tor can be connected in parallel with the internal transistor

to reduce the on-resistance for higher charge current. In

this case, an external blocking diode is required to prevent

current source pulls this pin up to the charge pump

potential when turned on and a 40

µA current source pulls

it down to ground to turn it off. If an overcurrent condition

is detected, the GATE pin is immediately pulled to ground.

switch is turned on or off. The slew rate control prevents

excessive current from the capacitor located in the wall

adapter from flowing into the battery when the pass

transistor is turned on. The voltage at this pin is internally

clamped to 12V above the BAT pin.

BAT (Pin 8): Battery Sense Input Pin. This pin is clamped

to 4.7V if the battery is disconnected while charging. An

internal resistor divider presets the final float voltage to

4.2V.

If the voltage at the BAT pin drops 150mV below final float

voltage after the charge cycle has ended, the timer resets

and a new charge cycle begins.

LTC1730EGN-4

GND (Pins 1, 8, 9, 16): Refer to LTC1730ES8-4.2

SENSE (Pin 2): Refer to LTC1730ES8-4.2

ACPR (Pin 4): Wall Adapter Present Open-Drain Output.

When the input voltage (wall adapter) is applied to the

LTC1730, this pin is pulled to ground by an internal