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參數(shù)資料
| 型號(hào)： | MAX7481 |
| 廠商： | Maxim Integrated Products, Inc. |
| 英文描述： | Bidirectional Video Filters/Buffers for Composite and S-Video Portable Media Devices |
| 中文描述： | 雙向視頻濾波器/緩沖器，用于復(fù)合視頻及S端子便攜式多媒體產(chǎn)品 |
| 文件頁(yè)數(shù)： | 6/13頁(yè) |
| 文件大?。?/td> | 872K |
| 代理商： | MAX7481 |
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M
Bidirectional Video Filters/Buffers for Composite
and S-Video Portable Media Devices
6
_______________________________________________________________________________________
Pin Description (continued)
PIN
22
24
25
26
27
28
NAME
IN4
V
SS
CPV
SS
C1N
CPGND
C1P
FUNCTION
Video Input 4
Negative Power Supply. Connect to CPV
SS
.
Charge-Pump Negative Power Supply. Bypass with a low-ESR 1μF capacitor to CPGND.
Charge-Pump Flying Capacitor Negative Terminal. Connect a low-ESR 1μF capacitor from C1P to C1N.
Charge-Pump Power Ground
Charge-Pump Flying Capacitor Positive Terminal. Connect a low-ESR 1μF capacitor from C1P to C1N.
—
EP
Exposed Pad. Internally connected to GND. Do not route any PCB traces directly under the package.
Connect EP to GND for improved heat dissipation.
Detailed Description
The MAX7481/MAX7482 bidirectional video filters and
buffers are ideal for portable video applications where
low-voltage, low-power operation is critical and applica-
tions that require both analog video inputs and outputs.
The MAX7481/MAX7482 provide the reconstruction fil-
ter and line drivers for both composite video (CVBS)
and Y/C (S-Video) for playback, while providing anti-
In playback mode, the IN1 and IN2 inputs are enabled
while the IN3, IN4, and IN5 inputs are disabled. The
MAX7481/MAX7482 provide the filtered Y/C outputs at
OUT1 and OUT2, and the composite output at OUT3.
In record mode, IN1 and IN2 are disabled while IN3,
IN4, and IN5 are enabled. Switches connecting OUT1
to GND, OUT2 to GND, and OUT3 to GND are turned
on. These switches provide low-impedance paths to
ground so that the same 75
Ω
external resistors that
connect the playback outputs (OUT1, OUT2, and
OUT3) and the external device can be used as termi-
nating resistors for the recording signal source.
Inputs IN3, IN4, and IN5 require AC-coupling capacitors
because the signal from the external video source can
be DC level-shifted and an internal clamp uses these
capacitors to restore the blanking level to GND. The
internal clamp operates only on signals coming from the
external source due to the uncertainty in the DC offset.
The gain in either direction is fixed at +6dB for the
MAX7481. The MAX7482 output buffers have a gain of
+7dB in playback mode and +6dB in record mode.
The MAX7481/MAX7482 feature DirectDrive technology
that allows the blanking level to stay at GND in a single
supply system. The MAX7481/MAX7482 internally gener-
ate a negative supply voltage from an inverting charge
pump and internal linear regulator. The regulated nega-
tive supply allows output buffers to drive 2V
P-P
video sig-
nals without exceeding operating voltage limits.
Comparison Between DirectDrive Output
and AC-Coupled Output
DirectDrive refers to the connection of the video signal
from the MAX7481/MAX7482 to an external device with-
out requiring large series AC-coupling capacitors in a
single supply system. The actual level of the video sig-
nal varies less with a DirectDrive output than an AC-
coupled output. The video-signal average can change
greatly depending upon the picture content. With an
AC-coupled output, the average changes according to
the time constant formed by the series capacitor and
series resistance (usually 150
Ω
). For example, Figure 1
shows an AC-coupled video signal alternating between
a completely black screen and a completely white
screen. Notice the excursion of the video signal as the
screen changes. With a DirectDrive amplifier, the black
level is held at ground. The video signal is constrained
between -0.3V to +0.7V. Figure 2 shows the video sig-
nal from a DirectDrive amplifier with the same input sig-
nal as the AC-coupled system.
The large series AC-coupling capacitors create a high-
pass filter. Since the lowest frequency in video is the
frame rate, which can be between 24Hz and 30Hz, the
pole of the highpass filter should ideally be an order of
magnitude lower in frequency than the frame rate.
Therefore, the AC-coupling capacitor must be very
large, typically from 220μF to 3000μF. For space-con-
strained equipment, the series capacitor is unaccept-
able. Changing from a single series capacitor to a SAG
network that requires two smaller capacitors can
reduce space, but increases cost.
Playback Mode
Playback mode takes the video signal from the video
processor and provides the reconstruction filter and line
drive for both composite and Y/C video outputs. Figure 3
shows a signal flow diagram and Figure 4 shows the sig-
nal flow from the video processor to an external media
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| MAX7482 | Bidirectional Video Filters/Buffers for Composite and S-Video Portable Media Devices |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
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