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LTC4069

Standalone 750mA Li-Ion Battery Charger in 2 × 2 DFN with NTC Thermistor Input

Linear Technology 

LTC4069

Pin Functions

GND (Pin 1): Ground.

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 cur-

rent drops to 10% of 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 (75% duty cycle). When the NTC

pin voltage rises above 0.76 • VCC or drops below 0.35

• VCC, the CHRG pin pulses at a frequency of 2Hz (25%

duty cycle).

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

rent to the battery and regulates the final float voltage to

4.2V. 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

provides 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 LTC4069 enters shutdown mode, dropping IBAT

to about 1µA.

NTC (Pin 5): Input to the NTC (Negative Temperature

Coefficient) Thermistor Temperature Monitoring Circuit.

Under normal operation, connect a thermistor from the

NTC pin to ground and a resistor of equal value from the

NTC pin to VCC. When the voltage at this pin drops below

0.35 • VCC at hot temperatures or rises above 0.76 • VCC

at cold, charging is suspended, the internal timer is frozen

and the CHRG pin output will start to pulse at 2Hz. Pulling

this pin below 0.016 • VCC disables the NTC feature. There

is approximately 3°C of temperature hysteresis associated

with each of the input comparator’s thresholds.

PROG (Pin 6): Charge Current Program and Charge

Current 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

•

1000

Floating the PROG pin puts the charger in shutdown mode.

In shutdown mode, the LTC4069 has less than 20µA supply

current and about 1µA battery drain current.

Exposed Pad (Pin 7): Ground. The Exposed Pad must

be soldered to the PCB ground to provide both electrical

contact and rated thermal performance.

4069fc

6

For more information www.linear.com/LTC4069

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