参数资料
型号: NCS2561SQT1G
厂商: ON Semiconductor
文件页数: 9/11页
文件大小: 0K
描述: IC OP AMP HS W/FILTER SC-88
标准包装: 3,000
应用: 滤波器
电路数: 1
电流 - 电源: 6mA
电流 - 输出 / 通道: 50mA
电压 - 电源,单路/双路(±): 2.7 V ~ 3.3 V
安装类型: 表面贴装
封装/外壳: 6-TSSOP,SC-88,SOT-363
供应商设备封装: SC-88
包装: 带卷 (TR)
其它名称: NCS2561SQT1G-ND
NCS2561SQT1GOSTR
NCS2561
http://onsemi.com
7
Sag Correction
Video drivers that do not incorporate sag compensation
traditionally recommend a large coupling capacitor (220
mF)
on the output of the video driver. Larger output coupling
capacitors (
≥ 470 mF) are often chosen by design engineers
when the application allows this (SetTop Box). A larger
output coupling capacitor allows a lower cutoff frequency
to avoid field tilt effects; however in portable applications
there is a tradeoff between large and expensive coupling
capacitors, and a coupling configuration to saving space.
The sag compensation circuitry allows the reduction of this
output coupling capacitor value by inducing peaking at the
lower cutoff frequency of the high pass filter. The highpass
filter is created by the coupling capacitor and the load
resistor (1/(2
pRLCout), and this peaking lowers the cutoff
frequency. Simulation results provided in Figure 11 show
the effect of the sag compensation at the low cutoff
frequency.
Gain VS Frequency
30
25
20
15
10
5
0
5
10
15
20
1
10
100
1000
10000
100000 1000000 10000000 1E+08
Frequency (Hz)
Gain
(dB)
Cout = 22uF
Cout = 47uF
Cout = 67uF
Cout = 100uF
Cout = 220uF
Figure 11. Simulation Results with Csag = 22 mF and Variable Cout
Calculations show that a 220
mF output capacitor
produces a low cutoff frequency of 5 Hz, and a 470
mF
capacitor will give a low cutoff frequency at 2.6 Hz. The
cutoff frequency (3 dB) is defined by the equation:
1/(2
pRLCout). In the case where no sag is used (Figure 14),
a low Cout value can adversely affect the low cutoff
frequency; the cutoff frequency will be in the critical 50 Hz
or 60 Hz frequencies. This undesirable affect will manifest
itself as field tilt. Due to the SAG correction the large output
capacitor is reduced without degrading the video
performances by the use of two smaller and cheaper output
capacitors.
Figure 12. Sag Correction Configuration
1 V
0 V
1Vpp
Level
Shifter
+
GND
Enable
NCS2561
Vcc
IN
2pole
filter
2.7V to 3.3V
OUT
SAG
Video
DAC
47 mF / 67 mF
22 mF
75 W
TV
Rs
Enable
Vcc
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