NSVD4001DR2G Datasheet, PDF (4/8 Pages) ON Semiconductor – High Current LED Driver

NUD4001, NSVD4001
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
V_{in 1}
Boost 2
R_{ext 3}
GND
4
NUD4001
Current
Set Point
8 ^Iout
7 ^Iout
6 ^Iout
5 ^Iout
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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