ZXLD1360

Issue 1 - March 2007

22

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© Zetex Semiconductors plc 2007

Note that the device power dissipation will most often be a maximum at minimum supply

voltage. It will also increase if the efficiency of the circuit is low. This may result from the use of

unsuitable coils, or excessive parasitic output capacitance on the switch output.

Thermal compensation of output current

High luminance LEDs often need to be supplied with a temperature compensated current in order

to maintain stable and reliable operation at all drive levels. The LEDs are usually mounted

remotely from the device so, for this reason, the temperature coefficients of the internal circuits

for the ZXLD1360 have been optimized to minimize the change in output current when no

compensation is employed. If output current compensation is required, it is possible to use an

external temperature sensing network - normally using Negative Temperature Coefficient (NTC)

thermistors and/or diodes, mounted very close to the LED(s). The output of the sensing network

can be used to drive the ADJ pin in order to reduce output current with increasing temperature.

Maximum Power Dissipation

0

100

200

300

400

500

600

700

800

900

1000

1100

-50

-30

-10

10

30

50

70

90

110

130

150

Ambient Temperature (Deg C)