Datasheet
OPA362DisablePulse
EqualizationPulses
OPA362Ouput
PulledHIGH;
NoVideoLoad
Connected
VerticalSyncPulses
1stVerticalSyncPulse
D:1.84V
@:1.84V
D:305mV
@:3.00mV
OPA362DisablePulse
EqualizationPulses
OPA362OutputPulledLOW
BecauseofVideoLoad
VerticalSyncPulses
FirstVerticalSyncPulse
OPA362
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........................................................................................................................................................................................ SBOS480 –SEPTEMBER 2009
Internal Level Shift vertical sync pulse. For the detection, a simple pull-up
resistor to the processor logic supply is used on the
Many common video DACs embedded in digital
output of the OPA362. The voltage level is pulled low
media processors, such as the OMAP343x
if the TV (or other video equipment) is connected, or
processors from Texas Instruments, operate on a
high if nothing is connected. A GPIO in the processor
single supply (no negative supply). Typically, the
can be used to read this logic level and decide if a
lowest point of the sync pulse output by these video
video load is connected. Figure 25 shows a scope
DACs is close to 0V. With a 0V input, the output of a
plot with the TV disconnected and Figure 26 shows a
common single-supply op amp saturates at a voltage
scope plot with the TV connected; the upper line in
greater than 0V. This effect would clip the sync pulse,
both figures is the disable pulse. See Figure 27 for a
and therefore degrade the video signal integrity. The
circuit drawing that shows how to use the TV-detect
OPA362 employs an internal level shift circuit to
signal to disable or enable the OPA362.
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.
Figure 25. Output of OPA362 Pulled Up to 1.8V
During Disable: TV Disconnected
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
Figure 26. Output of OPA362 Pulled Down: TV
output of the device. In order to detect a TV load, the
Connected
OPA362 is briefly turned off, ideally during the first
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