LTC1732-4.2 Ver la hoja de datos (PDF) - Linear Technology

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LTC1732-4.2

Lithium-Ion Linear Battery Charger Controller

Linear Technology 

LTC1732-4/LTC1732-4.2

PIN FUNCTIONS

BAT (Pin 1): Battery Sense Input. A bypass capacitor of

10µF or more is required to keep the loop stable when the

battery is not connected. A precision internal resistor

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

divider is disconnected in sleep mode to reduce the

current drain on the battery.

SEL (Pin 2): 4.1V/4.2V Battery Selection Input Pin. Ground-

ing this pin will set the output float voltage to 4.1V per cell,

while connecting to VCC will set the voltage to 4.2V per cell.

For the LTC1732-4.2, the SEL pin must be connected to

VCC.

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

the battery is being charged, 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 35µA current

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

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

source will be disconnected and the CHRG pin is forced

into a high impedance state.

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

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

a capacitor, CTIMER, to GND. The timer period is tTIMER

(hours) = (CTIMER • 3 hours)/(0.1µF). When the TIMER pin

is connected to VCC, the timer is disabled, the constant-

voltage mode is disabled and the chip will operate in

constant-current mode only. Shorting the TIMER pin to

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-

ing a resistor, RPROG to ground. The charge current is IBAT

= (VPROG • 800Ω)/(RPROG • RSENSE). The IC can be forced

into shutdown by floating the PROG pin and allowing the

internal 2.5µA current source to pull the pin above the

2.457V shutdown threshold voltage.

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

or PNP Transistor. If a PNP pass transistor is used, select

a high beta transistor to minimize the charge current error

due to the base current.

VCC (Pin 8): Positive Input Supply Voltage. When VBAT is

within 54mV of VCC, the LTC1732 is forced into sleep

mode, dropping ICC to 7µA. VCC ranges from 4.5V to 12V.

Bypass this pin with a 1µF capacitor.

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

RSENSE, must be connected from VCC to the SENSE pin.

This resistor is chosen using the following equation:

RSENSE = (VPROG • 800Ω)/(RPROG • IBAT)

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

input voltage (wall adapter) greater than the undervoltage

lockout threshold is applied to the LTC1732, this pin is

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

capable of sinking 5mA to drive an external LED.

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