A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
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.
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 1uF 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 and reduce the frequency of dimming, 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 startup threshold
(VUVLO). 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
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 15 -
AITSEMI [ AiT Semiconductor ]
