LTC4080
9
4080fc
For more information www.linear.com/LTC4080
PIN FUNCTIONS
BAT (Pin 1): Charge Current Output and Buck Regulator
Input. Provides charge current to the battery and regu-
lates the final float voltage to 4.2V. An internal precision
resistor divider from this pin sets the float voltage and is
disconnected in charger shutdown mode. This pin should
be decoupled with a low ESR capacitor for low noise buck
operation.
V
CC
(Pin 2): Positive Input Supply Voltage. This pin pro-
vides power to the battery charger. V
CC
can range from
3.75V to 5.5V. This pin should be bypassed with at least a
1µF capacitor. When V
CC
is less than 32mV above the B
AT
pin voltage, the battery charger enters shutdown mode.
EN_CHRG (Pin 3): Enable Input Pin for the Battery Char-
ger. Pulling this pin above the manual shutdown threshold
(V
IH
) puts the LTC4080 charger in shutdown mode, thus
stopping the charge cycle. In battery charger shutdown
mode, the LTC4080 has less than 10µA supply current
and less than 5µA battery drain current if the regulator is
not running. Enable is the default state, but the pin should
be tied to GND if unused.
PROG (Pin 4): Charge Current Program and Charge Cur-
rent Monitor Pin. Connecting a 1% resistor, RPROG, to
ground programs the charge current. When charging in
constant-current mode, this pin servos to 1V. In all modes,
the voltage on this pin can be used to measure the charge
current using the following formula:
I
BAT
=
PROG
R
•400
ACPR (Pin 5): Open-Drain Power Supply Status Output.
When V
CC
is greater than the undervoltage lockout thresh-
old (3.6V) and greater than V
BAT
+ 80mV, the ACPR pin will
be pulled to ground; otherwise the pin is high impedance.
CHRG (Pin 6): Open-Drain Charge Status Output. The
charge status indicator pin has three states: pull-down,
high impedance state, and pulse at 2Hz. This output can
be used as a logic interface or as an LED driver. 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, the CHRG pin is
forced to a high impedance state. When the battery volt-
age remains below 2.9V for one quarter of the full charge
time, the battery is considered defective, and the CHRG
pin pulses at a frequency of 2Hz with 75% duty cycle.
FB (Pin 7): Feedback Pin for the Buck Regulator. A resistor
divider from the regulator’s output to the FB pin programs
the output voltage. Servo value for this pin is 0.8V.
MODE (Pin 8): Burst Mode Enable Pin. Tie this pin high
to force the LTC4080 regulator into Burst Mode operation
for all load conditions. Tie this pin low to force constant-
frequency mode operation for all load conditions. Do not
float this pin.
EN_BUCK (Pin 9): Enable Input Pin for the Switching
Regulator.
Pull this pin high to enable the regulator, pull
low to shut down. Do not float this pin.
SW (Pin 10): Switch Pin for the Buck Regulator. Minimize
the length of the metal trace connected to this pin. Place
the inductor as close to this pin as possible.
GND (Pin 11): Ground. This pin is the back of the Exposed
Pad package and must be soldered to the PCB for electrical
connection and rated thermal performance.
