zxld1352 Zetex Semiconductors plc., zxld1352 Datasheet - Page 18

• Manufacturer Part Number: zxld1352
• Description: 350ma Led Driver With Internal Switch And Enhanced Pwm Dimming Range
• Manufacturer: Zetex Semiconductors plc.

Reducing output ripple
Peak to peak ripple current in the LED can be reduced, if required, by shunting a capacitor C
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-
up threshold (V
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
below gives details for power derating. This assumes the device to be mounted on a 25mm
with 1oz copper standing in still air.
Issue 1 - August 2008
© Diodes Incorporated 2008
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18
ZXLD1352
www.diodes.com
www.zetex.com
2
PCB
led