AIC1648 データシートの表示（PDF） - Analog Intergrations

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AIC1648

Built-in OVP White LED Step-Up Converter

Analog Intergrations 

AIC1648

Dimming Control

There are three different ways of dimming control

circuits as follows:

1. Using a PWM signal

PWM brightness control provides the widest

dimming range by pulsing the LEDs on and off at

full and zero current, respectively. The change of

average LED current depends on the duty cycle of

the PWM signal. Typically, a 0.1kHz to 1kHz

PWM signal is used. Two applications of PWM

dimming with AIC1648 are shown in Figure 16

and Figure 17. One, as Figure 16, uses PWM

signal to drive SHDN pin directly for dimming

control. The other, as Figure 17, employs PWM

signal going through a resistor to drive FB pin. If

the SHDN pin is used, the increase of duty cycle

results in LED brightness enhancement. If the FB

pin is used, on the contrary, the increase of duty

cycle will decrease its brightness. In this

application, LEDs are dimmed by FB pin and

turned off completely by SHDN .

2. Using a DC Voltage

For some applications, the preferred method of a

dimming control uses a variable DC voltage to

adjust LED current. The dimming control using a

DC voltage is shown in Figure 18. With a VDC

ranging from 0V to 5V, the selection of resistors in

Figure 18 results in dimming control of LED

current from 20mA to 0mA, respectively.

3. Using a Filtered PWM Signal

Filtered PWM signal can be considered as an

adjustable DC voltage. It can be used to replace

the variable DC voltage source in dimming

control. The circuit is shown in Figure 19.

VIN

C1

1µF

PWM

L

10µH

VIN SW

SHDN OVP

GND FB

AIC1648

D1

RB521S-30

C2

1µF

RFB

4.7Ω

Fig. 16 Dimming Control with a PWM Signal

VIN

C1

1µF

L

D1

10µH

VIN SW

RB521S-30

C2

1µF

SHDN OVP

GND FB

R2

AIC1648

PWM 51K

R1

1K

RFB

4.7Ω

Fig. 17 Dimming Control Using a PWM Signal

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