A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
forward current is always constant, therefore the LED color does not vary with brightness as it does with
analog dimming. Pulsing the current provides precise brightness control while preserving the color purity.
The dimming frequency of A8180 can be as high as 20 kHz.
Shutdown Mode
Taking the ADJ pin to a voltage below 0.2V will turn off the output and the supply current will fall to a low
standby level of 50μA nominal.
Soft-start
An external capacitor from the ADJ pin to ground will provide soft-start delay, by increasing the time taken for
the voltage on this pin to rise to the turn-on threshold. Adding capacitance increases this delay by
approximately 0.06ms/nF.
Inherent Open-Circuit LED Protection
If the connection to the LED(s) is open circuited, the coil is isolated from the LX pin of the chip, so the device
will not be damaged.
Capacitor Selection
A low ESR capacitor should be used for input decoupling, as the ESR of this capacitor appears in series with
the supply source impedance and lowers overall efficiency. This capacitor has to supply the relatively high
peak current to the coil and smooth the current ripple on the input supply. A minimum value of 4.7uF is
acceptable if the input source is close to the device, but higher values will improve performance at lower input
voltages, especially when the source impedance is high. The input capacitor should be placed as close as
possible to the IC.
For maximum stability over temperature and voltage, capacitors with X7R, X5R, or better dielectric are
recommended. Capacitors with Y5V dielectric are not suitable for decoupling in this application and should
not be used.
Inductor Selection
Recommended inductor values for the A8180 are in the range 27uH to 100uH. Higher values of inductance
are recommended at lower output current in order to minimize errors due to switching delays, which result in
increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output
current over the supply voltage range. The inductor should be mounted as close to the device as possible with
low resistance connections to the LX and VIN pins. The chosen coil should have a saturation current higher
than the peak output current and a continuous current rating above the required mean output current. Suitable
coils for use with the A8180 are listed in the table below:
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 13 -
AITSEMI [ AiT Semiconductor ]
