LTC3405 datasheet(7/18 Pages) LINEAR

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LTC4065L/

LTC4065LX/LTC4065L-4.1

4065lfb

PIN FUNCTIONS

GND (Pin 1, Exposed Pad Pin 7): Ground. The Exposed

Pad must be soldered to the PCB ground to provide both

electrical contact and rated thermal performance.

CHRG (Pin 2): Open-Drain Charge Status Output. The

charge status indicator pin has three states: pull-down,

pulse at 2Hz and high impedance state. This output can

be used as a logic interface or as an LED driver. 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, the CHRG pin is

forced to a high impedance state. If the battery voltage

remains below 2.9V for one quarter of the charge time, the

battery is considered defective and the CHRG pin pulses

at a frequency of 2Hz.

BAT (Pin 3): Charge Current Output. Provides charge cur-

rent to the battery and regulates the final float voltage (4.2V

for LTC4065L/LTC4065LX and 4.1V for LTC4065L-4.1).

An internal precision resistor divider on this pin sets the

float voltage and is disconnected in shutdown mode.

VCC (Pin 4): Positive Input Supply Voltage. This pin pro-

vides power to the charger. VCC can range from 3.75V

to 5.5V. This pin should be bypassed with at least a 1μF

capacitor. When VCC is within 32mV of the BAT pin volt-

age, the LTC4065L enters shutdown mode, dropping IBAT

to about 1μA.

EN (Pin 5): Enable Input Pin. Pulling this pin above the

manual shutdown threshold (VMS is typically 0.82V) puts

the LTC4065L in shutdown mode. In shutdown mode, the

LTC4065L has less than 20μA supply current and less than

1μA battery drain current. Enable is the default state, but

the pin should be tied to GND if unused.

PROG (Pin 6): Charge Current Program and Charge Cur-

rent Monitor Pin. Connecting a 1% resistor, RPROG, to

ground programs the charge current. 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:

IBAT =

VPROG

RPROG

• 205

Floating the PROG pin sets the charge current to zero.

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