LTC1731-4.1 Datasheet, PDF (5/12 Pages) Linear Technology – Single Cell Lithium-Ion Linear Battery Charger Controllers

LTC1731-4.1/LTC1731-4.2
PIN FUNCTIONS
BAT (Pin 1): Battery Sense Input. A bypass capacitor of at
least 10µF is required to keep the loop stable when the
battery is not connected. A precision internal resistor
divider sets the final float potential on this pin. The resistor
divider is disconnected in sleep mode.
CHRG (Pin 2): Open-Drain Charge Status Output. When
the battery is being charged, the CHRG pin is pulled low by
an internal N-channel MOSFET. When the charge current
drops to 10% of the full-scale current for at least 0.32
seconds, the N-channel MOSFET turns off and a 100µA
current source is connected from the CHRG pin to GND.
When the timer runs out or the input supply is removed,
the current source will be disconnected and the CHRG pin
is forced into a high impedance state.
TIMER (Pin 3): Timer Capacitor and Constant-Voltage
Mode Disable Input Pin. The timer period is set by placing
a capacitor, C_TIMER, to GND. The timer period is t_TIMER =
(C_TIMER • 3 hours)/(0.1µF). When the TIMER pin is
connected to V_CC, the constant-voltage mode and the
timer are disabled, the chip will operate in constant-
current mode only. Short the TIMER pin to GND to disable
the internal timer function and the C/10 function.
GND (Pin 4): Ground Connection.
PROG (Pin 5): Charge Current Program and Shutdown
Input Pin. The charge current is programmed by connect-
ing a resistor, R_PROG to ground. The charge current is I_BAT
= (V_PROG • 800Ω)/(R_PROG • R_SENSE). The IC can be forced
into shutdown by floating the PROG pin. An internal 2.5µA
current source will pull the pin above the shutdown
threshold voltage when the program resistor (R_PROG) is
disconnected.
DRV (Pin 6): Drive Output Pin for the P-Channel MOSFET
or PNP Transistor. The impedance is high at this pin,
therefore, a high beta PNP pass transistor should be used.
The DRV pin is internally clamped to 6.5V below V_CC.
V_CC (Pin 7): Positive Input Supply Voltage. When V_BAT is
within 54mV of V_CC, the LTC1731 is forced into sleep
mode, dropping I_CC to 7µA. V_CC ranges from 4.5V to 12V.
Bypass this pin with a 1µF capacitor.
SENSE (Pin 8): Current Sense Input. A sense resistor,
R_SENSE, must be connected from V_CC to the SENSE pin.
This resistor is chosen using the following equation:
R_SENSE = (V_PROG • 800Ω)/(R_PROG • I_BAT)
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