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參數(shù)資料
| 型號： | THS7372IPWR |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 4 CHANNEL, VIDEO AMPLIFIER, PDSO14 |
| 封裝： | GREEN, PLASTIC, TSSOP-14 |
| 文件頁數(shù)： | 27/49頁 |
| 文件大?。?/td> | 1768K |
| 代理商： | THS7372IPWR |
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Level
Shift
Internal
Circuitry
+3.3V
800kW
R
PU
Input
Pin
Input
C
0.1 F
m
IN
V
=V
DC
S
800kW
800k
+R
W
PU
SBOS578
– AUGUST 2011
To allow for both dc- and ac-coupling in the same part, the THS7372 incorporates an 800-k
resistor to ground.
Although a true constant current sink is preferred over a resistor, there can be issues when the voltage is near
ground. This configuration can cause the current sink transistor to saturate and cause potential problems with the
signal. The 800-k
resistor is large enough to not impact a dc-coupled DAC termination. For discharging an
ac-coupled source, Ohm
’s Law is used. If the video signal is 1 V, then there is 1 V/800 k = 1.25-μA of
discharge current. If more hum rejection is desired or there is a loss of sync occurring, then simply decrease the
0.1-
μF input coupling capacitor. A decrease from 0.1 μF to 0.047 μF increases the hum rejection by a factor of
2.1. Alternatively, an external pull-down resistor to ground may be added that decreases the overall resistance
and ultimately increases the discharge current.
To ensure proper stability of the ac STC control loop, the source impedance must be less than 1 k
with the
input capacitor in place. Otherwise, there is a possibility of the control loop ringing, which may appear on the
output of the THS7372. Because most DACs or encoders use resistors (typically less than 300
Ω) to establish
the voltage, meeting the less than 1-k
requirement is easily done. However, if the source impedance looking
from the THS7372 input perspective is very high, then simply adding a 1-k
resistor to GND ensures proper
operation of the THS7372.
INPUT MODE OF OPERATION: AC BIAS
Sync-tip clamps work very well for signals that have horizontal and/or vertical syncs associated with them;
however, some video signals do not have a sync embedded within the signal. If ac-coupling of these signals is
desired, then a dc bias is required to properly set the dc operating point within the THS7372. This function is
easily accomplished with the THS7372 by simply adding an external pull-up resistor to the positive power supply,
as shown in Figure 87.
Figure 87. AC-Bias Input Mode Circuit Configuration
The dc voltage appearing at the input pin is equal to Equation 1:
(1)
The THS7372 allowable input range is approximately 0 V to (VS+ – 1.5 V), allowing for a very wide input voltage
range. As such, the input dc bias point is very flexible, with the output dc bias point being the primary factor. For
example, if the output dc bias point is desired to be 1.6 V on a 3.3-V supply, then the input dc bias point should
be (1.6 V
– 300 mV)/2 = 0.65 V. Thus, the pull-up resistor calculates to approximately 3.3 M, resulting in
0.644 V. If the output dc-bias point is desired to be 1.6 V with a 5-V power supply, then the pull-up resistor
calculates to approximately 5.36 M
.
Keep in mind that the internal 800-k
resistor has approximately a ±20% variance. As such, the calculations
should take this variance into account. For the 0.644-V example above, using an ideal 3.3-M
resistor, the input
dc bias voltage is approximately 0.644 V
±0.1 V.
The value of the output bias voltage is very flexible and is left to each individual design. It is important to ensure
that the signal does not clip or saturate the video signal. Thus, it is recommended to ensure the output bias
voltage is between 0.9 V and (VS+ – 1 V). For 100% color saturated CVBS or signals with Macrovision
, the
CVBS signal can reach up to 1.23 VPP at the input, or 2.46 VPP at the output of the THS7372. In contrast, other
signals are typically 1 VPP or 0.7 VPP at the input which translate to an output voltage of 2 VPP or 1.4 VPP. The
output bias voltage must account for a worst-case situation, depending on the signals involved.
Copyright
2011, Texas Instruments Incorporated
33
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| THS7372PWEVM | 功能描述:放大器 IC 開發(fā)工具 THS7372 EVAL MOD RoHS:否 制造商:International Rectifier 產(chǎn)品:Demonstration Boards 類型:Power Amplifiers 工具用于評估:IR4302 工作電源電壓:13 V to 23 V |
| THS7373 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:4-Channel Video Amplifier with 1-SD and 3-HD Sixth-Order Filters and 6-dB Gain |
| THS7373_10 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:4-Channel Video Amplifier with 1-SD and 3-HD Sixth-Order Filters and 6-dB Gain |
| THS7373EVM | 功能描述:放大器 IC 開發(fā)工具 THS7373EVM Eval Mod RoHS:否 制造商:International Rectifier 產(chǎn)品:Demonstration Boards 類型:Power Amplifiers 工具用于評估:IR4302 工作電源電壓:13 V to 23 V |
| THS7373IPW | 功能描述:視頻放大器 4-Ch Video Amp RoHS:否 制造商:ON Semiconductor 通道數(shù)量:4 電源類型: 工作電源電壓:3.3 V, 5 V 電源電流: 最小工作溫度: 最大工作溫度: 封裝 / 箱體:TSSOP-14 封裝:Reel |
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