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SM8121AD Datasheet(PDF) 10 Page - Nippon Precision Circuits Inc

No. de pieza SM8121AD
Descripción Electrónicos  White LED Driver IC
Download  19 Pages
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Fabricante Electrónico  NPC [Nippon Precision Circuits Inc]
Página de inicio  http://www.npc.co.jp/en
Logo NPC - Nippon Precision Circuits Inc

SM8121AD Datasheet(HTML) 10 Page - Nippon Precision Circuits Inc

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SM8121A
NIPPON PRECISION CIRCUITS INC.—10
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 (50k
Ω) and capacitor C1 (0.1µF) provide a PWM
signal frequency range of 1kHz to 1MHz.
Brightness adjustment using FB pin (DC voltage input)
When the brightness is controlled by DC voltage (VDC) connected to resistor R3, the LED current (ILED) is
given by equation 1.
If the values R1 = 30
Ω, 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.
If the values R1 = 30
Ω, 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.
Taking the above diagram as an example, inserting the values R1 = 30
Ω, 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).
Brightness adjustment circuit using FB pin
(DC voltage input)
SW
VSS
FB
SM8121
R1
30
SBD
DC Voltage
0 to 3V
R3
100k
R2
20k
VDD
CE
COUT
1.0
µF
L
10
µH
CIN
4.7
µF
VIN
3.6V
LED
DC voltage vs. LED current
0
5
10
15
20
0.0
0.5
1.0
1.5
2.0
2.5
3.0
DC voltage [V]
R1
R2
× (VDC − VFB)
R3
ILED =
VFB
... (1)
20,000
× (0 − 0.5)
100,000
30
30
ILED ==
=
0.5
0.6
20mA
... (2)
20,000
× (3 − 0.5)
100,000
30
30
ILED ==
=
0.5
0
0mA
... (3)


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