NUD4001 Просмотр технического описания (PDF) - ON Semiconductor

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NUD4001

High Current LED Driver

ON Semiconductor 

NUD4001

APPLICATION INFORMATION

Design Guide

1. Define LED’s current:

a. ILED = 350 mA

2. Calculate Resistor Value for Rext:

a. Rext = Vsense (see Figure 2) / ILED

b. Rext = 0.7 (TJ = 25 °C)/ 0.350 = 2.0 W

3. Define Vin:

a. Per example in Figure 6, Vin = 12 V

4. Define VLED @ ILED per LED supplier’s data

sheet:

a. Per example in Figure 6,

VLED = 3.5 V + 3.5 V + 3.5 V = 10.5 V

5. Calculate Vdrop across the NUD4001 device:

a. Vdrop = Vin – Vsense – VLED

b. Vdrop = 12 V – 0.7 V (TJ = 25 °C) – 10.5 V

c. Vdrop = 0.8 V

Vin 1

Boost 2

Rext 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)

6. Calculate Power Dissipation on the NUD4001

device’s driver:

a. PD_driver = Vdrop * Iout

b. PD_driver = 0.8 V x 0.350 A

c. PD_driver = 0.280 Watts

7. Establish Power Dissipation on the NUD4001

device’s control circuit per Figure 4:

a. PD_control = Figure 4, for 12 V input voltage

b. PD_control = 0.055 W

8. Calculate Total Power Dissipation on the device:

a. PD_total = PD_driver + PD_control

b. PD_total = 0.280 W + 0.055 W = 0.335 W

9. If PD_total > 1.13 W (or derated value per

Figure 3), then select the most appropriate

recourse and repeat steps 1 through 8:

a. Reduce Vin

b. Reconfigure LED array to reduce Vdrop

c. Reduce Iout by increasing Rext

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 Rext.

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