SD42524

5.

Thermal compensation and linear dimming function

SD42524 has linear dimming and thermal compensation functions.

Linear dimming function: Set the output current by adjust the ratio of R1 and R2. The relation between voltage

on pin ADJ and output current Iout is shown below:

1.22V

V

DJ

A

≥

,

Rs

0.088

Iout

=

HANGZHOU SILAN MICROELECTRONICS CO.,LTD

REV:1.1

2009.06.26

Http://www.silan.com.cn

Page 5 of 11

1.22V

V

0.1V

DJ

A

<

<

,

1.22

V

Rs

0.088

DJ

A

×

=

Iout

Thermal compensation function: the application circuit is shown above, use NTC resistor to take place of R2 for

thermal compensation. In normal temperature, the voltage on R2 is higher than 1.22V, and 100% current is

delivered to output; when LED temperature detected by R2 is higher than the setting value Tth, the voltage on

R2 is lower than 1.22V, and output current will decrease following the rising temperature. Connect NTC R2 with

other resistor in series to get different LED falling curves under different current.

The relation between LED output current and temperature