LTC4079
7
4079f
For more information www.linear.com/LTC4079
pin FuncTions
IN (Pin 1): Input Supply Pin. This input provides power
to the battery charger. Bypass this pin with a ceramic
capacitor of at least 1µF.
EN (Pin 2): Enable Input. Charge current starts flowing
when this input rises above 1.190V, its regulation threshold.
When using a current limited power source, connect this
input to an external resistor divider from IN to GND to avoid
UVLO oscillations. This configuration can also be used
to maintain the source voltage (IN pin) at the maximum
power threshold (e.g., for solar panel). Pulling this pin
below 0.750V shuts down the device. This pin should
not be left floating.
PROG (Pin 3): Charge Current Program Pin. The current
out of this pin is 1/250th of the current out of the BAT
pin. A resistor connected from PROG to ground sets the
charge current in constant-current mode. This pin servos
to 1.190V during constant-current charging. Do not leave
this pin open. Limit parasitic capacitance on this node to
less than 50pF.
NTCBIAS (Pin 4): NTC Thermistor Bias Output. Connect
a low drift bias resistor from NTCBIAS to NTC pin, and
a thermistor from NTC pin to GND. The value of the bias
resistor is
typically equal to the nominal resistance of
the
thermistor at 25°C. Minimize parasitic capacitance
on this pin.
NTC (Pin 5): Input to the Battery Temperature Sense
Circuit. Connect the NTC pin to a negative temperature
coefficient (NTC) thermistor, which is typically co-packaged
with the battery, to signal the charger if the battery is too
hot or too cold to charge. The room temperature value
of the thermistor should be at least 2kΩ. If the battery’s
temperature is out of range, charging is paused until the
battery temperature re-enters the valid range. Connect a
1%, low drift bias resistor from NTCBIAS to NTC and a
thermistor from NTC to ground. Minimize parasitic ca
-
pacitance on this pin. Ti
e the NTC pin to GND to disable
battery temperature sensing.
TIMER (Pin 6): Timer Capacitor Input. A capacitor on this
pin sets the maximum duration for battery charging from
charger enable or from the beginning of a recharge cycle.
For maximum charge duration of t
TIMER
(in Hours), the
required capacitance value can be determined as follows:
C
TIMER
= (t
TIMER
• 18.2nF/Hr)
A typical value of C
TIMER
is 100nF which terminates the
charge cycle after 5½ hours. Minimize leakage on this pin
to maintain timer accuracy.
The
timer is disabled when this pin is tied to GND. In this
case charging terminates when the charge current falls
below 1/10th of the programmed charge current I
CHG
.
CHRG (Pin 7): Open-Drain Charge Status Output. Typically
pulled up to a voltage source through a resistor or a low
power LED and a resistor. This pin is pulled low by an
internal NMOS when LTC4079 is charging the battery.
The pin goes to high impedance when the charge current
drops below 1/10th of the programmed current, or the
charge cycle is timer terminated.
FBG (Pin 8): Ground Reference for Battery Voltage Divider.
This pin is connected to ground internally through an NMOS
switch when the battery is charging and disconnects the
battery voltage divider from GND when it is not needed.
When sensing the battery voltage the NMOS switch
presents a low resistance (R
FBG
=160Ω) to GND.
FB (Pin 9): Sense Pin for Divided Battery Voltage. This pin
servos to 1.170V (V
FB(CHG)
) during the constant-voltage
phase of the battery charge algorithm. The battery charge
voltage is set by using an appropriate resistor divider
from BAT to FB to FBG. Minimize leakage and
parasitic
capacitance on this pin.
BAT (Pin 10): Battery Charger Output. This pin provides
charge current to the battery.
GND (Exposed Pad Pin 11): Ground. The exposed pad
must be soldered to a continuous ground plane of the
printed circuit board for electrical connection and the rated
thermal performance.
