A8180
AiT Semiconductor Inc.
www.ait-ic.com
LED LIGHTING DRIVER
HIGH BRIGHTNESS LED DRIVER WITH INTERNAL SWITCH
L (uH)
33
47
68
100
DCR (Ω)
ISAT (A)
2.3
2
1.6
0.093
0.128
0.213
0.304
1.3
The inductor value should be chosen to maintain operating duty cycle and switch 'on'/'off' times within the
specified limits over the supply voltage and load current range.
The following equations can be used as a guide.
LX Switch 'On' time
L x ΔI
IN - VLED -IAVG x (R
tON
=
V
S
+ R +RLX)
L
LX Switch 'Off' time
L x ΔI
+ IAVG x (R
tOFF
=
V
LED + V
D
S
+ R )
L
Where:
L is the coil inductance (H)
RL is the coil resistance (Ω)
RS is the current sense resistance (Ω)
I
AVG is the required LED current (A)
ΔI is the coil peak-peak ripple current (A)
(Internally set to 0.3 x IAVG
VIN is the supply voltage (V)
)
VLED is the total LED forward voltage (V)
R
LX is the switch resistance (Ω) (=0.35Ω nominal)
VD is the diode forward voltage at the required load current (V)
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
REV3.0
- APR 2010 RELEASED, JAN 2017 UPDATED -
- 14 -
AITSEMI [ AiT Semiconductor ]
