LTC1730-4/LTC1730-4.2
5
sn1730 1730fs
PI FU CTIO S
UUU
LTC1730ES8-4.2
SENSE (Pin 1): Maximum Overcurrent Sense Input. A
sense resistor (R
SENSE
) should be connected from V
CC
to
the SENSE pin. When the voltage drop across R
SENSE
exceeds 100mV, the pass transistor immediately turns off
and turns back on after a 400ms time-out period (C
TIMER
= 0.1µF). The on-off cycle will continue, as long as the
overcurrent condition persists or until the timer runs out.
If overcurrent protection is not needed, short SENSE to
V
CC
.
V
CC
(Pin 2): Positive Input Supply Voltage (4.5V ≤ V
CC
≤
13.2V). Bypass this pin with a 1µF capacitor in series with
a 4.7Ω resistor. An RC network from the V
CC
pin to the
GATE pin is also required. The capacitor controls the slew
rate at the V
CC
pin, while the resistor limits the inrush
current when the input voltage is first applied. When the
pass transistor turns on, V
CC
ramps down in a controlled
manner, with a slope equal to 10µA/C. When the pass
transistor turns off, V
CC
ramps up with a slope of 40µA/C.
CHRG (Pin 3): Open-Drain Charge Status Output. When a
depleted battery is being charged, the CHRG pin is pulled
to ground by an N-MOSFET capable of driving an LED.
Once the duty cycle at the GATE pin drops below 10%, the
N-MOSFET turns off and a weak 40µA current source to
ground turns on to indicate a near end-of-charge (C/10)
condition. When a time-out occurs or the input supply is
removed, the CHRG pin goes high impedance.
GND (Pin 4): Electrical Ground Connection and provides
a thermal path from the IC to the PC board copper. Use
large copper pads and traces for maximum heat transfer.
TIMER (Pin 5): Timer Set Pin. The timer period is set by a
capacitor (C
TIMER
) to ground. The timer period is:
t
TIMER
= (C
TIMER
• 3Hr)/(0.1µF). The minimum ON time,
OFF time and the overcurrent time-out period are all set by
the same timer period.
NTC/SHDN (Pin 6): Input to the NTC (Negative Tempera-
ture Coefficient) Thermistor Monitoring and Shutdown
Circuitry. With an external 10kΩ NTC thermistor to ground
and a 1% resistor to V
CC
, this pin can sense the tempera-
ture of the battery pack and stop charging when the
temperature is out of range. When the voltage at this pin
drops below 0.5 • V
CC
, or 2V at hot temperature or rises
above 0.875 • V
CC
, or 3.5V at cold (with V
CC
= 4V), the
charge cycle is suspended and the internal timer is frozen.
The CHRG pin output status is not affected in this hold
state.
When this pin is pulled below 50mV, the IC goes into the
shutdown mode. The charging stops (the GATE pin is
pulled to ground) the timer is reset and the CHRG pin goes
into a high impedance state.
GATE (Pin 7): Gate Drive Output Pin for Internal and
External Pass Transistors. An external N-MOSFET transis-
tor can be connected in parallel with the internal transistor
to reduce the on-resistance for higher charge current. In
this case, an external blocking diode is required to prevent
damage to the battery if V
CC
is shorted to ground. A 10µA
current source pulls this pin up to the charge pump
potential when turned on and a 40µA current source pulls
it down to ground to turn it off. If an overcurrent condition
is detected, the GATE pin is immediately pulled to ground.
A series RC network from the GATE to the V
CC
pin is
required to control the slew rate at the V
CC
pin when the
switch is turned on or off. The slew rate control prevents
excessive current from the capacitor located in the wall
adapter from flowing into the battery when the pass
transistor is turned on. The voltage at this pin is internally
clamped to 12V above the BAT pin.
BAT (Pin 8): Battery Sense Input Pin. This pin is clamped
to 4.7V if the battery is disconnected while charging. An
internal resistor divider presets the final float voltage to
4.2V.
If the voltage at the BAT pin drops 150mV below final float
voltage after the charge cycle has ended, the timer resets
and a new charge cycle begins.
LTC1730EGN-4
GND (Pins 1, 8, 9, 16): Refer to LTC1730ES8-4.2
SENSE (Pin 2): Refer to LTC1730ES8-4.2
V
CC
(Pin 3): Refer to LTC1730ES8-4.2
ACPR (Pin 4): Wall Adapter Present Open-Drain Output.
When the input voltage (wall adapter) is applied to the
LTC1730, this pin is pulled to ground by an internal
