SM8120AH Ver la hoja de datos (PDF) - Nippon Precision Circuits

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Fabricante

SM8120AH

White LED Driver IC

Nippon Precision Circuits  

SM8120A

BRIGHTNESS ADJUSTMENT

Brightness Adjustment using FB Pin

The LED brightness can be adjusted using an input DC control voltage connected through resistor R3 to the FB

pin. Alternatively, the brightness can be controlled by a PWM signal by adding a low-pass filter comprising

resistor R4 and capacitor C1. The PWM signal frequency range is determined by the low-pass filter coeffi-

cients. For example, the recommended values for resistor R4 (50kΩ) and capacitor C1 (0.1µF) provide a PWM

signal frequency range of 1kHz to 1MHz.

Brightness adjustment using FB pin (DC voltage input)

VIN

3.6V

L

22µH

CIN

4.7µF

DC Voltage

0 to 3V

SBD

SW

VDD

VSS

FB

CE

R3

100kΩ

COUT

1.0µF

LED

R2

20kΩ

R1

30Ω

Brightness adjustment circuit using FB pin

(DC voltage input)

20

15

10

5

0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

DC voltage [V]

DC voltage vs. LED current

When the brightness is controlled by DC voltage (VDC) connected to resistor R3, the LED current (ILED) is

given by equation 1.

VFB − R2 × (VDC − VFB)

R3

ILED =

R1

... (1)

If the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V, and VDC = 0V are inserted in equation 1, the

LED current ILED = 20mA, as shown in equation 2.

0.5 − 20,000 × (0 − 0.5)

ILED =

100,000

= 0.6 = 20mA

30

30

... (2)

If the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V, and VDC = 3V are inserted in equation 1, the

LED current ILED = 0mA, as shown in equation 3.

0.5 − 20,000 × (3 − 0.5)

ILED =

100,000

= 0 = 0mA

30

30

... (3)

Taking the above diagram as an example, inserting the values R1 = 30Ω, R2 = 20kΩ, R3 = 100kΩ, VFB = 0.5V,

and VDC = 0 to 3V into equation 1 gives the maximum LED current ILED of 20mA when VDC = 0V (equation

2) and the minimum LED current ILED of 0mA when VDC = 3V (equation 3).

NIPPON PRECISION CIRCUITS INC.—7

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