ZXLD1366_10 DIODES [Diodes Incorporated], ZXLD1366_10 Datasheet - Page 24

• Manufacturer Part Number: ZXLD1366_10
• Description: HIGH ACCURACY 1A, 60V LED DRIVER WITH INTERNAL SWITCH
• Manufacturer: DIODES [Diodes Incorporated]

A Product Line of
Diodes Incorporated
ZXLD1366
Diode Selection
For maximum efficiency and performance, the rectifier (D1) should be a fast low capacitance Schottky diode* with low
reverse leakage at the maximum operating voltage and temperature.
They also provide better efficiency than silicon diodes, due to a combination of lower forward voltage and reduced recovery
time.
It is important to select parts with a peak current rating above the peak coil current and a continuous current rating higher
than the maximum output load current. It is very important to consider the reverse leakage of the diode when operating
above 85°C. Excess leakage will increase the power dissipation in the device and if close to the load may create a thermal
runaway condition.
The higher forward voltage and overshoot due to reverse recovery time in silicon diodes will increase the peak voltage on
the LX output. If a silicon diode is used, care should be taken to ensure that the total voltage appearing on the LX pin
including supply ripple, does not exceed the specified maximum value.
*A suitable Schottky diode would be B3100 (Diodes Inc).
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:
D1
V
IN
Rs
LED
Cled
L1
V
I
LX
IN
SENSE
ZXLD1366
Figure 6 Reduce Output Ripple
A value of 1mF 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.
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ZXLD1366
June 2010
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© Diodes Incorporated
Document number: DS31992 Rev. 5 - 2