5

LTC4050

4050f

BAT (Pin 1): Battery Sense Input. A precision internal

resistor divider on this pin sets the final float voltage. The

resistor divider is disconnected in sleep mode to reduce

the current drain on the battery. A bypass capacitor of

10

µF or more is required to keep the loop stable when the

battery is not connected.

NTC (Pin 2): Thermistor Interface Input. A 10k

Ω Dale

Curve 2 NTC thermistor (or other 10k

Ω NTC thermistor

with a room temperature beta of around 3400) is con-

nected from this pin to ground. The charge cycle will be

disabled and the timer will be placed on hold if the

thermistor temperature is above 50

°C or below 0°C.

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

the battery is charging, the CHRG pin is pulled low by an

internal N-channel MOSFET. When the charge current

drops to 10% of the full-scale current for more than 15ms,

the N-channel MOSFET turns off and a 32

µA current

source is connected from the CHRG pin to GND. When the

timer runs out or the input supply is removed, the current

source is disconnected and the CHRG pin becomes high

impedance.

TIMER (Pin 4): Timer Capacitor and Constant-Voltage

Mode Disable Input Pin. The timer period is set by placing

GND will disable the internal timer function and the C/10

function.

GND (Pin 5): Ground.

PROG (Pin 6): Charge Current Program and Shutdown

Input Pin. The charge current is programmed by connect-

into shutdown by floating the PROG pin and allowing the

internal 2.3

µAcurrentsourcetopullthepinabovethe3.6V

shutdown threshold voltage.

DRV (Pin 7): Drive Output Pin for the P-Channel MOSFET

or PNP Transistor. The impedance is high at this pin,

therefore, if a PNP pass transistor is used, it must have

high gain.

from 4.5V to 10V. Bypass this pin with a 1

µF capacitor.

SENSE (Pin 9): Current Sense Input. A sense resistor,

Select a resistor value that will develop approximately

100mV at the programmed full-scale charge current.

This resistor is chosen using the following equation:

ACPR (Pin 10): Wall Adapter Present Output. When the

input voltage (wall adaptor) is applied to the LTC4050, this

pin is pulled to ground by an internal N-channel MOSFET

that is capable of sinking 5mA suitable for driving an

external LED.