6
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 4.7µF or greater bypass
capacitor to ground.
D
OUT
(Pin 2): TTL Data Output Signal for the Serial
Interface. D
OUT
and D
IN
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).
D
IN
(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 C
F
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, C
F
along with an internal R
F
= 1k form a
lowpass filter to average the voltage across the sense
resistor.
PIN FUNCTIONS
UUU
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 R
SENSE
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 V
DAC
.
The battery charging current is equal to V
DAC
/R
SENSE
.
In the gas gauge mode the voltage across the Sense pin
is filtered by an RC network (R
F
and C
F
), 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.
V
IN
(Pin 12): General Purpose ADC Input.
T
AMB
(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.
T
BAT
(Pin 14): Battery Temperature Input. Connect to an
external NTC thermistor network. Tie to REG if not used.
V
BAT
(Pin 15): Battery Input. An internal voltage divider is
connected between the V
BAT
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 V
DD
.
V
DD
(Pin 18): Positive Supply Voltage. 4.5V < V
DD
< 16V.
