LTC4097
8
4097f
PIN FUNCTIONS
DCIN (Pin 1): Wall Adapter Input Supply Pin. Provides
power to the battery charger. The maximum supply
current is 1.2A. This pin should be bypassed with a 1µF
capacitor.
USBIN (Pin 2): USB Input Supply Pin. Provides power to
the battery charger. The maximum supply current is 1A.
This pin should be bypassed with a 1µF capacitor.
VNTC (Pin 3): Output Bias Voltage for NTC. A resistor
from this pin to the NTC pin sets up the bias for an NTC
thermistor. When the DCIN or USBIN pin voltage is suffi cient
to begin charging (i.e. when the DCIN or USBIN supply
is greater than the undervoltage lockout thresholds and
at least 100mV or 150mV, respectively, above the battery
terminal), the VNTC pin is connected to the appropriate
input through an internal P-channel MOSFET. If suffi cient
voltage to charge is not present on DCIN or USBIN the
VNTC pin is high impedance. This output can source up
to 120mA.
⎯
C
⎯
H
⎯
R
⎯
G (Pin 4): Open-Drain Charge Status Output. When
the LTC4097 is charging, the
⎯
C
⎯
H
⎯
R
⎯
G pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is com-
pleted,
⎯
C
⎯
H
⎯
R
⎯
G becomes high impedance. This output can
sink up to 10mA, making it suitable for driving a LED.
SUSP (Pin 5): Charge Enable Input. A logic low on this
pin enables the charger. If left fl oating, an internal 3.4MΩ
pull-down resistor defaults the LTC4097 to charge mode.
Pull this pin high for shutdown.
NTC (Pin 6): Input to the NTC (Negative Temperature
Coeffi cient) Thermistor Temperature Monitoring Circuit.
For normal operation, connect a thermistor from the NTC
pin to ground and a resistor of equal value from the NTC
pin to VNTC. When the voltage at this pin drops below
0.349 • VNTC at hot temperatures or rises above
0.765 • VNTC at cold, charging is suspended and the
⎯
C
⎯
H
⎯
R
⎯
G pin output will keep the state in which it was be-
fore the event (low-Z or high-Z). Pulling this pin below
0.017 • VNTC disables the NTC feature. There is approxi-
mately 2°C of temperature hysteresis associated with each
of the input comparator’s thresholds.
HPWR (Pin 7): HPWR Enable Input. Used to control the
amount of current drawn from the USB port. A logic high
on the HPWR pin sets the charge current to 100% of the
current programmed by the IUSB pin. A logic low on the
HPWR pin sets the charge current to 20% of the current
programmed by the IUSB pin. An internal 3.4MΩ pull-down
resistor defaults the HPWR pin to its low current state.
ITERM (Pin 8): Charge Termination Current Threshold
Program. The termination current threshold, I
TERMINATE
, is
set by connecting a resistor, R
ITERM
, to ground. I
TERMINATE
is set by the following formula:
I
V
R
TERMINATE
ITERM
=
100
When the battery current, I
BAT
, falls below the termination
threshold, charging stops and the
⎯
C
⎯
H
⎯
R
⎯
G output becomes
high impedance.
