LTC4077
7
4077fa
USBIN (Pin 1): USB Input Supply Pin. Provides power to
the battery charger. The maximum supply current is 650mA.
This pin should be bypassed with a 1µF capacitor.
IUSB (Pin 2): Charge Current Program for High 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
V
R
BAT
IUSB
IUSB
= • 1000
IUSBL (Pin 3): Charge Current Program for Low USB Power.
The charge current is set by connecting a resistor, R
IUSBL
,
to ground. When charging in constant current mode, this
pin servos to 0.2V. The voltage on this pin can be used to
measure the battery current delivered from the USB input
using the following formula:
I
V
R
BAT
IUSBL
IUSBL
= •200
P
W
R (Pin 4): Open-Drain Power Supply Status Output.
When the DCIN or USBIN pin voltage is sufficient to begin
charging (i.e. when the supply is greater than the under-
voltage lockout threshold and at least 180mV above the
battery terminal), the
P
W
R pin is pulled low by an internal
N-channel MOSFET. Otherwise
P
W
R is high impedance.
This output is capable of sinking up to 10mA, making it
suitable for driving an LED.
C
H
R
G (Pin 5): Open-Drain Charge Status Output. When
the LTC4077 is charging, the
C
H
R
G pin is pulled low by
an internal N-channel MOSFET. When the charge cycle is
completed,
C
H
R
G becomes high impedance. This output
is capable of sinking up to 10mA, making it suitable for
driving an LED.
E
N (Pin 6): Charge Enable Input. A logic low on this pin
enables the charger. If left floating, an internal 2MΩ pull-
down resistor defaults the LTC4077 to charge mode. Pull
this pin high for shutdown.
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 current limit at the current
programmed by the IUSB pin. A logic low on the HPWR
pin sets the current limit at the current programmed by the
IUSBL pin. An internal 2MΩ pull-down resistor defaults
the HPWR pin to its low current state.
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
V
R
BAT
IDC
IDC
= • 1000
BAT (Pin 9): Charger Output. This pin provides charge
current to the battery and regulates the final float voltage
to 4.2V.
DCIN (Pin 10): Wall Adapter Input Supply Pin. Provides
power to the battery charger. The maximum supply
current is 950mA. This 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.
