LTC1733
6
sn1733 1733fs
UU
U
PI FU CTIO S
CHRG: Open-Drain Charge Status Output. 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 N-channel
MOSFET latches off and a 25µA current source is con-
nected from the CHRG pin to ground. The C/10 latch can
be cleared by momentarily pulling the PROG pin above the
2.15V shutdown threshold, or by toggling V
CC
. When the
timer runs out or the input supply is removed, the current
source is disconnected and the CHRG pin is forced to a
high impedance state.
V
CC
: Positive Input Supply Voltage. When V
CC
is within
30mV of V
BAT
or less than the undervoltage lockout
threshold, the LTC1733 enters sleep mode, dropping I
BAT
to less than 5µA. V
CC
can range from 4.5V to 6.5V. Bypass
this pin with at least a 4.7µF ceramic capacitor to ground.
FAULT: Open-Drain Fault Status Output. The FAULT open-
drain logic signal indicates that the charger has timed out
under trickle charge conditions (1/4 of total time period) or
the NTC comparator is indicating an out-of-range battery
temperature condition. When V
BAT
is less that 2.48V,
trickle charging activates whereby the charge current
drops to one tenth of its programmed value and the timer
period is reduced by a factor of four. When one fourth of
the timing period has elapsed, if V
BAT
is still less than
2.48V, trickle charging stops and the FAULT pin latches to
ground. The fault can be cleared by toggling V
CC
, momen-
tarily pulling the PROG pin above the 2.15V shutdown
threshold, or pulling the BAT pin above 2.48V. If the NTC
comparator is indicating an out-of-range battery tempera-
ture condition, then the FAULT pin will pull to ground until
the temperature returns to the acceptable range.
TIMER: Timer Capacitor. The timer period is set by placing
a capacitor, C
TIMER
, to ground. The timer period is:
Time (Hours) = (C
TIMER
• 3 hr)/(0.1µF)
Short the TIMER pin to ground to disable the internal timer
function.
GND: Ground. Connect exposed back package to ground.
NTC: Input to the NTC (Negative Temperature Coefficient)
Thermistor Temperature Monitoring Circuit. With an ex-
ternal 10kΩ NTC thermistor to ground and a 1% resistor
to V
CC
, this pin can sense the temperature of the battery
pack and stop charging when it is out of range. When the
voltage at this pin drops below (0.5)•(V
CC
) at hot tempera-
tures or rises above (0.875)•(V
CC
) at cold, charging is
suspended and the internal timer is frozen. The CHRG pin
output status is not affected in this hold state. The FAULT
pin is pulled to ground, but not latched. When the tempera-
ture returns to an acceptable range, charging will resume
and the FAULT pin is released. The NTC feature can be
disabled by grounding the NTC pin.
PROG: Charge Current Program, Shutdown Input and
Charge Current Monitor Pin. The charge current is pro-
grammed by connecting a resistor, R
PROG
to ground.
When in constant-current mode, the LTC1733 servos the
PROG pin voltage to 1.5V. In all modes the voltage on the
PROG pin can be used to measure the charge current as
follows:
I
CHG
= (V
PROG
/R
PROG
) • 1000.
The IC can be forced into shutdown by pulling the PROG
pin above the 2.15V shutdown threshold voltage (note: it
will not be pulled up when allowed to float).
SEL: 4.1V/4.2V Battery Selection Input. Grounding this
pin sets the battery float voltage to 4.1V, while connecting
to V
CC
sets the voltage to 4.2V.
BAT: Charge Current Output. A bypass capacitor of at least
1µF with a 1Ω series resistor is required to minimize ripple
voltage when the battery is not present. A precision
internal resistor divider sets the final float potential on this
pin. The internal resistor divider is disconnected in sleep
and shutdown modes.
ACPR: Open-Drain Power Supply Status Output. When
V
CC
is greater than the undervoltage lockout threshold
and at least 30mV above V
BAT
, the ACPR pin will pull to
ground. Otherwise, the pin is forced to a high impedance
state.
