Datasheet

2

Rev. 1.0, 2007-03-20

TLE4309

Circuit Description

An external shunt resistor in the ground path of the connected LEDs senses the LED

current. A regulation loop maintains the voltage drop across the shunt resistor at a

constant level. Selecting the shunt resistance permits to adjust the appropriate constant

current . The output current calculates

(1)

where

V

equation applies in a range of 0.39

shown as a function of the reference resistance.

Figure 1

Block Diagram and Typical Application Circuit

During operation, the LED brightness is modifiable by adjusting the duty cycle at the

PWM/EN input. This allows to dim the LEDs during operation or adapt the output current

to different LED luminosity classes.

A low signal at the PWM/EN input sets the IC into sleep mode consuming less than 1 µA.

Due to its high input impedance, the PWM/EN pin can be used as an enable input.

Connect the pin directly to the supply line, if its function is not needed.

The minimum supply voltage calculates as the sum of the LED forward voltages, the

TLE4309 dropout voltage and the maximum voltage drop across the reference resistor

R

,

V

REF

R

REF

------------

=

T L E 430 9_B LOCKDIA GRA M+ AP PCIRCUIT .V SD

Bandgap

Reference

4

GND

5REF

7

Q

I

1

PWM

/ EN

2

Temp.

Shutdown

Bias Supply

R

RE F

+12V

Logic

100nF

TLE 4309