LTC1325CSW datasheet(6/24 Pages) LINER

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LTC1325

REG (Pin 1): Internal Regulator Output. The regulator

provides a steady 3.072V to the internal analog circuitry

and provides a temperature stable reference voltage for

generating MCV, HTF, LTF and thermistor bias voltages

with external resistors. Requires a 4.7

µF or greater bypass

capacitor to ground.

DOUT (Pin 2): TTL Data Output Signal for the Serial

Interface. DOUT and DIN may be tied together to form a

3-wire interface, or remain separated to form a 4-wire

interface. Data is transmitted on the falling edge of CLK

(Pin 5).

DIN (Pin 3): TTL Data Input Signal for the Serial Interface.

The data is latched into the chip on the rising edge of the

CLK (Pin 5).

CS (Pin 4): TTL Chip Select Signal for the Serial Interface.

CLK (Pin 5): TTL Clock for the Serial Interface.

LTF (Pin 6): Minimum Allowable Battery Temperature

Analog Input. LTF may be generated by a resistive divider

between REG (Pin 1) and ground.

MCV (Pin 7): Maximum Allowable Cell Voltage Analog

Input. MCV may be generated by a resistive divider be-

tween REG (Pin 1) and ground.

HTF (Pin 8): Maximum Allowable Battery Temperature

Analog Input. HTF may be generated by a resistive divider

between REG (Pin 1) and ground.

GND (Pin 9): Ground.

FILTER (Pin 10): The external filter capacitor CF is con-

nected to this pin. The filter capacitor is connected to the

output of the internal resistive divider across the battery to

reduce the switching noise while charging. In the gas

gauge mode, CF along with an internal RF = 1k form a

lowpass filter to average the voltage across the sense

resistor.

PIN FUNCTIONS

SENSE (Pin 11): The Sense pin controls the switching of

the 111kHz PWM constant current source in the charging

mode. The Sense pin is connected to an external sense

resistor RSENSE and the negative side of the battery. The

charging loop forces the average voltage at the Sense pin

to equal a programmable internal reference voltage VDAC.

The battery charging current is equal to VDAC/RSENSE.

In the gas gauge mode the voltage across the Sense pin

is filtered by an RC network (RF and CF), amplified by

an inverting gain of four, then multiplexed to the ADC so

the average discharge current through the battery may

be measured and the total charge leaving the battery

calculated.

VIN (Pin 12): General Purpose ADC Input.

TAMB (Pin 13): Ambient Temperature Input. Connect to an

external thermistor network. Tie to REG if not used. May

be used as another general purpose ADC input.

TBAT (Pin 14): Battery Temperature Input. Connect to an

external NTC thermistor network. Tie to REG if not used.

VBAT (Pin 15): Battery Input. An internal voltage divider is

connected between the VBAT and Sense pins to normalize

all battery measurements to one cell voltage. The divider

is programmable to the following ratios: 1/1, 1/2, 1/3 . . .

1/15, 1/16. In shutdown and gas gauge modes the divider

is disconnected.

DIS (Pin 16): Active High Discharge Control Pin. Used

to turn on an external transistor which discharges the

battery.

PGATE (Pin 17): FET Driver Output. Swings from GND

to VDD.

VDD (Pin 18): Positive Supply Voltage. 4.5V < VDD < 16V.

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