LTC1731-84 Просмотр технического описания (PDF) - Linear Technology

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LTC1731-84

Lithium-Ion Linear Battery Charger Controller

Linear Technology 

LTC1731-8.2/LTC1731-8.4

PIN FUNCTIONS

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

least 10µF is required to keep the loop stable when the

battery is not connected. A precision internal resistive

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

divider is disconnected in sleep mode.

CHRG (Pin 2): 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 at least 0.32

seconds, the N-channel MOSFET turns off and a 100µA

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 3): Timer Capacitor and Constant-Voltage

Mode Disable Input Pin. A capacitor CTIMER connected

from this pin to ground sets a 30 hour/µF time period for

charge termination. When the TIMER pin is connected to

VCC, the constant-voltage mode and the timer is disabled

and the IC will operate in constant-current mode only.

Short the TIMER pin to GND to disable the internal timer

and the C/10 functions.

GND (Pin 4): Ground.

PROG (Pin 5): 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 6): Drive Output Pin for the P-Channel MOSFET

or PNP Transistor. If a PNP transistor is used, it must have

high gain (see Applications Information section). The DRV

pin is internally clamped to 6.5V below VCC.

VCC (Pin 7): Input Supply Voltage. VCC ranges from 8.8V

to 12V when charging. If VCC drops below VBAT + 54mV,

for example when the input supply is disconnected, then

the IC enters sleep mode with ICC < 30µA. Bypass this pin

with a 1µF capacitor.

SENSE (Pin 8): Current Sense Input. Connect this pin to

the sense resistor. Choose the resistor value using the

following equation:

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

sn1731 17318fs

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