ZXLD1362

Document number: DS33472 Rev. 6 - 2

21 of 25

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March 2014

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ZXLD1362

Reducing Output Ripple

Peak to peak ripple current in the LED(s) can be reduced, if required, by shunting a capacitor Cled across the LED(s) as shown below:

 

LX

ZXLD1362

Rs

L1

Cled

LED

D1

A value of 1

μF will reduce the supply 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.

By adding this capacitor the current waveform through the LED(s) changes from a triangular ramp to a more sinusoidal version without altering

the mean current value.

Operation at Low Supply Voltage

Below the under-voltage lockout threshold (VSD) the drive to the output transistor is turned off to prevent device operation with excessive on-

resistance of the output transistor. The output transistor is not full enhanced until the supply voltage exceeds approximately 17V. At supply

If the supply voltage is always less than 30V continuous an alternative device is available, the ZXLD1360 or the AL8805.

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.