ZXLD1350

Issue 6 - April 2007

18

www.zetex.com

© Zetex Semiconductors plc 2007

Reducing output ripple

across the LED(s) as shown below:

A value of 1 F will reduce nominal ripple current by a factor three (approx.). Proportionally lower

ripple can be achieved with higher capacitor values. Note that the capacitor will not affect

operating frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of

LED voltage.

Operation at low supply voltage

The internal regulator disables the drive to the switch until the supply has risen above the start-

supply voltage below the specified minimum value, the switch duty cycle will be high and the

device power dissipation will be at a maximum. Care should be taken to avoid operating the

device under such conditions in the application, in order to minimize the risk of exceeding the

maximum allowed die temperature. (See next section on thermal considerations).

Note that when driving loads of two or more LEDs, the forward drop will normally be sufficient

to prevent the device from switching below approximately 6V. This will minimize the risk of

damage to the device.

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

with 1oz copper standing in still air.

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