LTC4078/LTC4078X
7
4078xfb
PIN FUNCTIONS
USBIN (Pin 1): USB Input Supply Pin. This input provides
power to the battery charger assuming a voltage greater
than V
UVUSB
and less than V
OVUSB
is present (typically
3.95V to 6V respectively). However, the DCIN input will
take priority if a voltage greater than V
UVDC
is present at
DCIN (typically 4.15V). The USBIN input allows charge
currents up to 850mA. This pin should be bypassed with
a 1μF capacitor.
IUSB (Pin 2): Charge Current Program for USB Power.
The charge current is set by connecting a resistor, R
IUSB
,
to ground. When charging in constant-current mode, this
pin servos to 1V. The voltage on this pin can be used to
measure the battery current delivered from the USB input
using the following formula:
I
BAT
=
V
IUSB
R
IUSB
• 1000
ITERM (Pin 3): 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
TER MINATE
=
100V
R
ITERM
When the battery current, I
BAT
, falls below the termination
threshold, charging stops and the CHRG output becomes
high impedance. This pin is internally clamped to approxi-
mately 1.5V. Driving this pin to voltages beyond the clamp
voltage should be avoided.
PWR (Pin 4): Open-Drain Power Supply Status Output.
When the DCIN or USBIN pin voltage is valid to begin charg-
ing (i.e. when the supply is greater than the undervoltage
lockout threshold, less than the overvoltage lockout thresh-
old and at least 120mV above the battery terminal), the
PWR pin is pulled low by an internal N-channel MOSFET.
Otherwise PWR is high impedance. This output is capable
of driving an LED.
CHRG (Pin 5): Open-Drain Charge Status Output. When the
LTC4078/LTC4078X are charging, the CHRG pin is pulled
low by an internal N-channel MOSFET. When the charge
cycle is completed, CHRG becomes high impedance. This
output is capable of driving an LED.
ENABLE (Pin 6): Enable Input. When the LTC4078/LTC4078X
are charging from the DCIN source, a logic low on this
pin enables the charger. When the LTC4078/LTC4078X are
charging from the USBIN source, a logic high on this pin
enables the charger. If this input is left fl oating, an internal
2MΩ pulldown resistor defaults the LTC4078/LTC4078X
to charge when a wall adapter is applied and to shut down
if only the USB source is applied.
BATDET (Pin 7): Battery Detection Input. When the volt-
age on this pin falls below V
BDET
(typically 1.75V), the
charger is on and ready for charging a battery. If this
input is left fl oating, an internal pull-up resistor will dis-
able charging.
IDC (Pin 8): Charge Current Program for Wall Adapter
Power. The charge current is set by connecting a resis-
tor, R
IDC
, to ground. When charging in constant-current
mode, this pin servos to 1V. The voltage on this pin can
be used to measure the battery current delivered from the
DC input using the following formula:
I
BAT
=
V
IDC
R
IDC
• 1000
BAT (Pin 9): Battery Charger Output. This pin provides
charge current to the battery and regulates the fi nal fl oat
voltage to 4.2V.
DCIN (Pin 10): Wall Adapter Input Supply Pin. This input
provides power to the battery charger assuming a voltage
greater than V
UVDC
and less than V
OVDC
is present (typi-
cally 4.15V to 6V respectively). A valid voltage on the DCIN
input will always take priority over the USBIN input. The
DCIN input allows charge currents up to 950mA. This pin
should be bypassed with a 1μF capacitor.
Exposed Pad (Pin 11): GND. The exposed backside of the
package is ground and must be soldered to PC board ground
for electrical connection and maximum heat transfer.
