OPA362 Datasheet, PDF (11/18 Pages) Texas Instruments – 3V VIDEO AMPLIFIER with Internal Gain and Filter in SC70

OPA362
www.ti.com ........................................................................................................................................................................................ SBOS480 – SEPTEMBER 2009
Internal Level Shift
Many common video DACs embedded in digital
media processors, such as the OMAP343x
processors from Texas Instruments, operate on a
single supply (no negative supply). Typically, the
lowest point of the sync pulse output by these video
DACs is close to 0V. With a 0V input, the output of a
common single-supply op amp saturates at a voltage
greater than 0V. This effect would clip the sync pulse,
and therefore degrade the video signal integrity. The
OPA362 employs an internal level shift circuit to
avoid clipping. The input signal is typically shifted by
approximately 11mV. This shift is well within the
linear output voltage range of the OPA362 with a
standard 150Ω video load.
Output Swing Capability
Figure 24 shows the true output swing capability of
the OPA362 by taking the tip of the input sync pulse
to a slightly negative voltage. Even when the output
sync tip is at 3mV, the output after the 75Ω series
termination continues to show no clipping of the sync
pulse.
vertical sync pulse. For the detection, a simple pull-up
resistor to the processor logic supply is used on the
output of the OPA362. The voltage level is pulled low
if the TV (or other video equipment) is connected, or
high if nothing is connected. A GPIO in the processor
can be used to read this logic level and decide if a
video load is connected. Figure 25 shows a scope
plot with the TV disconnected and Figure 26 shows a
scope plot with the TV connected; the upper line in
both figures is the disable pulse. See Figure 27 for a
circuit drawing that shows how to use the TV-detect
signal to disable or enable the OPA362.
OPA362 Disable Pulse
OPA362 Ouput
Pulled HIGH;
No Video Load
Connected
D: 1.84V
@: 1.84V
Equalization Pulses
1st Vertical Sync Pulse
Vertical Sync Pulses
D: 305mV
@: 3.00mV
Figure 25. Output of OPA362 Pulled Up to 1.8V
During Disable: TV Disconnected
OPA362 Disable Pulse
Figure 24. No Clipping of the Sync Pulse
TV-Detect Function
The TV-detection feature of the OPA362 works in
conjunction with the OMAP343x (or other processor)
to detect if a television is connected to the video
output of the device. In order to detect a TV load, the
OPA362 is briefly turned off, ideally during the first
OPA362 Output Pulled LOW
Because of Video Load
Equalization Pulses
First Vertical Sync Pulse
Vertical Sync Pulses
Figure 26. Output of OPA362 Pulled Down: TV
Connected
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Product Folder Link(s): OPA362
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