ZXLD1356

ZXLD1356

Document number: DS33470 Rev. 3 - 2

24 of 29

www.diodes.com

December 2010

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Thermal considerations

When operating the device at high ambient temperatures, or when driving maximum load current, care must be taken to avoid

exceeding the package power dissipation limits. The graph below gives details for power derating. This assumes the device to be

mounted on a (25mm)

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 ZXLD1356 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.

TSOT23-5

DFN3030-6

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-40

-25

-10

5

20

35

50

65

80

95

110

125

Ambient Temperature (°C)

140

Maximum Power Dissipation