NUD4001, NSVD4001
http://onsemi.com
4
APPLICATION INFORMATION
Design Guide
1. Define LED’s current:
a. I
LED
= 350 mA
2. Calculate Resistor Value for R
ext
:
a. R
ext
= V
sense
(see Figure 2) / I
LED
b. R
ext
= 0.7 (T
J
= 25 °C)/ 0.350 = 2.0 W
3. Define V
in
:
a. Per example in Figure 6, V
in
= 12 V
4. Define V
LED
@ I
LED
per LED supplier’s data
sheet:
a. Per example in Figure 6,
V
LED
= 3.5 V + 3.5 V + 3.5 V = 10.5 V
Figure 6. 12 V Application
(Series LED’s Array)
R
ext
GND
V
in
I
out
Current
Set Point
NUD4001
Boost
I
out
12 V
I
out
I
out
1
2
3
4
8
7
6
5
5. Calculate V
drop
across the NUD4001 device:
a. V
drop
= V
in
– V
sense
– V
LED
b. V
drop
= 12 V – 0.7 V (T
J
= 25 °C) – 10.5 V
c. V
drop
= 0.8 V
6. Calculate Power Dissipation on the NUD4001
device’s driver:
a. P
D_driver
= V
drop
* I
out
b. P
D_driver
= 0.8 V x 0.350 A
c. P
D_driver
= 0.280 Watts
7. Establish Power Dissipation on the NUD4001
device’s control circuit per Figure 4:
a. P
D_control
= Figure 4, for 12 V input voltage
b. P
D_control
= 0.055 W
8. Calculate Total Power Dissipation on the device:
a. P
D_total
= P
D_driver
+ P
D_control
b. P
D_total
= 0.280 W + 0.055 W = 0.335 W
9. If P
D_total
> 1.13 W (or derated value per
Figure 3), then select the most appropriate
recourse and repeat steps 1 through 8:
a. Reduce V
in
b. Reconfigure LED array to reduce V
drop
c. Reduce I
out
by increasing R
ext
d. Use external resistors or parallel device’s
configuration (see application note AND8156)
10. Calculate the junction temperaure using the
thermal information on Page 7 and refer to Figure
5 to check the output current drop due to the
calculated junction temperature. If desired,
compensate it by adjusting the value of R
ext
.
