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參數(shù)資料
| 型號(hào)： | SM8120AH |
| 廠商： | Seiko NPC Corporation |
| 元件分類： | LED驅(qū)動(dòng)器 |
| 英文描述： | White LED Driver IC |
| 中文描述： | 白光LED驅(qū)動(dòng)IC |
| 文件頁(yè)數(shù)： | 9/14頁(yè) |
| 文件大?。?/td> | 201K |
| 代理商： | SM8120AH |
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SM8120A
NIPPON PRECISION CIRCUITS INC.—9
Brightness Adjustment using CE Pin
The LED average current can be adjusted by controlling the duty of a PWM signal input on the CE pin. When
CE goes from LOW to HIGH, the soft start function operates (with 500μs constant soft start time) and, there-
fore, the LED average current ratio for a given PWM signal duty falls with increasing PWM signal frequency.
Taking this into consideration, the recommended PWM control signal has a frequency range of 100 to 400Hz
with duty cycle range of 10 to 90%.
When adjusting the brightness using the CE pin, a ripple voltage synchronized to the PWM signal is generated
across the output capacitor C
OUT
. The amplitude of the ripple voltage is determined by the number of LEDs
and their forward-bias voltage drop characteristics. If a ceramic capacitor is used for the output capacitor
C
OUT
, an audible noise may be generated due to the ceramic capacitor
’
s piezoelectric effect. The audible noise
level depends on the ceramic capacitor (capacitance, bias dependency, withstand voltage etc.), LEDs (number,
forward-bias voltage drop etc.), and mounting board (thickness, mounting conditions etc.), and thus should be
veri
fi
ed under actual conditions.
Brightness adjustment circuit using CE pin
VSS
R1
25
SBD
PWM signal
VDD
SW
CE
FB
OUT
C
μ
F
C
4.7
μ
F
3.6V
C
IN
V
IN
L
22
μ
H
LED
PWM signal duty vs. LED average current
PWM signal duty [%]
50
60
70
80
90
100
0.0
5.0
10.0
15.0
20.0
0
10
20
30
40
100Hz
400Hz
1000Hz
1400Hz
A
Alternatively, a tantalum capacitor or
fi
lm capacitor with low piezoelectric effect can be used as the output
capacitor C
OUT
to minimize the noise level, or the brightness can be adjusted using the FB pin as described
earlier. The audible noise generated when using the CE pin is not an inherent phenomena of the SM8120A
device, but of the brightness adjustment method employed.
Output voltage with LEDs ON
Output voltage with LEDs
OFF
CE input signal and output ripple voltage
20mA
C
OUT
3.5V
3.5V
3.5V
0.5V
11.0V
0mA
C
OUT
2.7V
2.7V
2.7V
0V
8.1V
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SM8121A | 制造商:NPC 制造商全稱:Nippon Precision Circuits Inc 功能描述:White LED Driver IC |
| SM8121AD | 制造商:NPC 制造商全稱:Nippon Precision Circuits Inc 功能描述:White LED Driver IC |
| SM8121AH | 制造商:NPC 制造商全稱:Nippon Precision Circuits Inc 功能描述:White LED Driver IC |
| SM8122A | 制造商:NPC 制造商全稱:Nippon Precision Circuits Inc 功能描述:White LED Driver IC |
| SM8122AD | 制造商:NPC 制造商全稱:Nippon Precision Circuits Inc 功能描述:White LED Driver IC |
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