Diodes ZXLD1360 - Manual (Page 19)

ZXLD1360
ZXLD1360
Document number: DS33471 Rev. 4 - 2
19 of 25
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March 2011
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Application Information (cont.)
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:
A value of 1µF 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
The internal regulator disables the drive to the switch until the supply has risen above the start-up threshold (V
SU
). Above this
threshold, the device will start to operate. However, with the 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). The drive to the switch is turned off when the supply voltage falls
below the under-voltage threshold (V
SD
). This prevents the switch working with excessive 'on' resistance under conditions
where the duty cycle is high.
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.
V
IN
V
IN
I
SENSE
LX
ZXLD1360
Rs
L1
Cled LED
D1