Data Sheet

2

Rev. 1.0, 2004-01-01

TLE 4242 G

Circuit Description

Figure 1

Block Diagram

An external shunt resistor in the ground path of the connected LEDs is used to sense the

LED current. A regulation loop helds the voltage drop at the shunt resistor on a constant

level of typ. 177 mV. Selecting the shunt resistance permits to adjust the appropriate

constant current level. The typ. output current calculates

(1)

where

V

equation applies in a range of 0.39

The output current is shown as a function of the reference resistance on Page 10. With

the PWM input the LED brightness can be regulated via duty cycle. Also PWM = L sets

the TLE 4242 in sleep mode resulting in a very low current consumption of << 1

µA typ.

Due to the high impedance of the PWM input (see “PWM Pin Input Current versus

PWM Voltage” on Page 11) the PWM pin can thus also be used as an enable input.

AEB03500.VSD

Bandgap

Reference

Bias Supply

Comparator

Status

Delay

4

GND

D

6

3

ST

5

REF

7

Q

I

1

PWM

2

I

Qtyp

,

V

REF

R

REF

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=