LTC4053-4.2
6
4053fa
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 30µA current source is con-
nected from the CHRG pin to ground. The C/10 latch can
be cleared by grounding the SHDN pin, momentarily, or
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 high impedance.
V
CC
: Positive Input Supply Voltage. When V
CC
is within
35mV of V
BAT
or less than the undervoltage lockout
threshold, the LTC4053 enters sleep mode, dropping I
BAT
to less than 3µA. V
CC
can range from 4.25V 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 or the NTC comparator is
indicating an out-of-range battery temperature condition.
If V
BAT
is less that 2.48V, trickle charging begins 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
, momentarily grounding the SHDN pin or
pulling the BAT pin above 2.48V. If the NTC comparator is
indicating an out-of-range battery temperature condition,
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. The exposed backside of the package is also
ground and must be soldered to the PC board for maxi-
mum heat transfer.
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 will be pulled to ground, but not latched. When the
temperature returns to an acceptable range, charging will
resume and the FAULT pin will be released. The NTC
feature can be disabled by grounding the NTC pin.
PROG: Charge Current Program and Charge Current Moni-
tor Pin. The charge current is programmed by connecting
a resistor, R
PROG
to ground. When in constant-current
mode, the LTC4053 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
BAT
= (V
PROG
/R
PROG
) • 1000.
SHDN: Shutdown Input Pin. Pulling the SHDN pin to
ground will put the LTC4053 into standby mode where the
BAT drain current is reduced to less than 3µA, and the
supply current is reduced to less than 25µA. For normal
operation, pull the SHDN pin up to V
CC
.
BAT: Charge Current Output. A bypass capacitor of at least
1µF with a 1Ω series resistor is required to keep the loop
stable 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 mode.
ACPR: Open-Drain Power Supply Status Output. When
V
CC
is greater than the undervoltage lockout threshold
and at least 35mV above V
BAT
, the ACPR pin will pull to
ground. Otherwise, the pin is high impedance.
