Diodes AP8802 Manuel d'utilisateur télécharger pdf (Page 7)

AP8802

1A LED STEP-DOWN CONVERTER

AP8802

Document number: DS31766 Rev. 9 - 2

7 of 19

www.diodes.com

May 2012

Application Information

LED Current Control

The LED current is controlled by the resistor R

SET

in Figure 14 connected between V

and SET. The nominal average output current in the

LED(s) with the CTRL pin open circuit is defined as:

SET

THD

LED

I = where V

THD

is the voltage between the V

and SET pins and is nominally 200mV.

Figure. 14 Typical Application Circuit for I

LED

= 1A

Inductor Selection

This section highlights how to select the inductor suitable for the application requirements in terms of switching frequency, LED current

accuracy and temperature.

0 50 100 150 200 250 300 350 400 450 500

INDUCTOR VALUE (µH)

Figure. 15 Switching Frequency vs. Inductor Value

100

150

220

470

100

150

220

470

150

220

470

Switching Frequency @ I = 700mA

LED

12V - 3 LEDs

24V - 5 LEDs

48V - 10 LEDs

FREQUENCY (kHz)

500

450

400

350

300

250

200

150

100

The inductor influences the LED current accuracy that the system is able to provide. The following section highlights how to select the

inductor in relation to the device packages and the LED current, while maintaining the chip temperature below 70°C.

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Diodes AP8802 Manuel d'utilisateur Page 7

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