
NUD4001, NSVD4001
APPLICATION INFORMATION
Design Guide
NUD4001
1. Define LED’s current:
a. I LED = 350 mA
V in
Boost
1
2
8
7
I out
I out
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
R ext
GND
3
4
Current
Set Point
6
5
I out
I out
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
12 V
Figure 6. 12 V Application
(Series LED’s Array)
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 .
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