LTC4069-4.4
6
406944fa
PIN FUNCTIONS
GND (Pin 1): Ground.
CHRG (Pin 2): Open-Drain Charge Status Output. The
charge status indicator pin has three states: pull-down,
pulse at 2Hz and high impedance state. 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. The pin becomes high
impedance when any of the following conditions occur:
the charge current drops below 10% of full-scale current,
the timer ends, or the charger is shut down. If the battery
voltage remains below 2.9V for one quarter of the charge
time, the battery is considered defective and the CHRG
pin pulses at a frequency of 2Hz (75% duty cycle). When
the NTC pin voltage rises above 0.76 • V
CC
or drops below
0.35 • V
CC
, the CHRG pin pulses at a frequency of 2Hz
(25% duty cycle).
BAT (Pin 3): Charge Current Output. Provides charge
current to the battery and regulates the fi nal fl oat voltage
to 4.4V. An internal precision resistor divider on this pin
sets the fl oat voltage and is disconnected in shutdown
mode.
VCC (Pin 4): Positive Input Supply Voltage. This pin
provides power to the 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 within 30mV of the BAT pin voltage,
the LTC4069-4.4 enters shutdown mode, dropping I
BAT
to about 1μA.
NTC (Pin 5): Input to the NTC (Negative Temperature
Coeffi cient) Thermistor Temperature Monitoring Circuit.
Under normal operation, connect a thermistor from the
NTC pin to ground and a resistor of equal value from the
NTC pin to V
CC
. When the voltage at this pin drops below
0.35 • V
CC
at hot temperatures or rises above 0.76 • V
CC
at cold, charging is suspended, the internal timer is frozen
and the CHRG pin output will start to pulse at 2Hz. Pulling
this pin below 0.016 • V
CC
disables the NTC feature. There
is approximately 3°C of temperature hysteresis associated
with each of the input comparator’s thresholds.
PROG (Pin 6): Charge Current Program and Charge
Current Monitor Pin. Connecting a 1% resistor, R
PROG
,
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
V
R
BAT
PROG
PROG
= • 1000
Floating the PROG pin puts the charger in shutdown mode.
In shutdown mode, the LTC4069-4.4 has less than 20μA
supply current and about 1μA battery drain current.
Exposed Pad (Pin 7): Ground. The Exposed Pad must
be soldered to the PCB ground to provide both electrical
contact and rated thermal performance.
