6
LTC4054-4.2/LTC4054X-4.2
405442xf
UU
U
PI FU CTIO S
CHRG (Pin 1): Open-Drain Charge Status Output. When
the battery is charging, the CHRG pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is
completed, a weak pull-down of approximately 20µA is
connected to the CHRG pin, indicating an “AC present”
condition. When the LTC4054 detects an undervoltage
lockout condition, CHRG is forced high impedance.
GND (Pin 2): Ground.
BAT (Pin 3): Charge Current Output. Provides charge
current to the battery and regulates the final float voltage
to 4.2V. An internal precision resistor divider from this pin
sets the float voltage which is disconnected in shutdown
mode.
V
CC
(Pin 4): Positive Input Supply Voltage. Provides
power to the charger. V
CC
can range from 4.25V to 6.5V
and should be bypassed with at least a 1µF capacitor.
When V
CC
drops to within 30mV of the BAT pin voltage, the
LTC4054 enters shutdown mode, dropping I
BAT
to less
than 2µA.
PROG (Pin 5): Charge Current Program, Charge Current
Monitor and Shutdown Pin. The charge current is pro-
grammed by connecting a 1% resistor, R
PROG
, to ground.
When charging in constant-current mode, this pin servos
to 1V. In all modes, the voltage on this pin can be used to
measure the charge current using the following formula:
I
BAT
= (V
PROG
/R
PROG
) • 1000
The PROG pin can also be used to shut down the charger.
Disconnecting the program resistor from ground allows
a 3µA current to pull the PROG pin high. When it reaches
the 1.21V shutdown threshold voltage, the charger enters
shutdown mode, charging stops and the input supply
current drops to 25µA. This pin is also clamped to
approximately 2.4V. Driving this pin to voltages beyond
the clamp voltage will draw currents as high as 1.5mA.
Reconnecting R
PROG
to ground will return the charger to
normal operation.
