LMH6601MG NSC [National Semiconductor], LMH6601MG Datasheet - Page 18

• Manufacturer Part Number: LMH6601MG
• Description: 250 MHz, 2.4V CMOS Op Amp with Shutdown
• Manufacturer: NSC [National Semiconductor]

www.national.com
Application Information
OVERLOAD RECOVERY AND SWING CLOSE TO RAILS
The LMH6601 can recover from an output overload in less
than 20 ns. See Figure 3 below for the input and output
scope photos:
In Figure 3, the input step function is set so that the output is
driven to one rail and then the other and then the output
recovery is measured from the time the input crosses 0V to
when the output reaches this point.
Also, when the LMH6601 input voltage range is exceeded
near the V
reversal, as some op amps do. This is particularly advanta-
geous in applications where output phase reversal has to be
avoided at all costs, such as in servo loop control among
others. This adds to the LMH6601’s set of features which
make this device easy to use.
In addition, the LMH6601’s output swing close to either rail is
well-behaved as can be seen in the scope photo of Figure 4.
FIGURE 4. LMH6601’s “Clean” Swing to Either Rail
FIGURE 3. LMH6601 Output Overload Recovery
+
rail, the output does not experience output phase
Waveform
(Continued)
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With some op amps, when the output approaches either one
or both rails and saturation starts to set in, there is significant
increase in the transistor parasitic capacitances which leads
to loss of Phase Margin. That is why with these devices,
there are sometimes hints of instability with output close to
the rails. With the LMH6601, as can be seen in Figure 4, the
output waveform remains free of instability throughout its
range of voltages.
SINGLE SUPPLY VIDEO APPLICATION
The LMH6601’s high speed and fast slew rate make it an
ideal choice for video amplifier and buffering applications.
There are cost benefits in having a single operating supply.
Single supply video systems can take advantage of the
LMH6601’s low supply voltage operation along with its ability
to operate with input common mode voltages at or slightly
below the V
eliminating or reducing the value of the input and output AC
coupling capacitors commonly employed in single supply
video applications. This Application section shows some
circuit techniques used to help in doing just that.
DC COUPLED, SINGLE SUPPLY BASEBAND VIDEO
AMPLIFIER/DRIVER
The LMH6601 output can swing very close to either rail to
maximize the output dynamic range which is of particular
interest when operating in a low voltage single supply envi-
ronment. Under light output load conditions, the output can
swing as close as a few milli-volts of either rail. This also
allows a video amplifier to preserve the video black level for
excellent video integrity. In the example shown below in
Figure 5, the baseband video output is amplified and buff-
ered by the LMH6601 which then drives the 75Ω back ter-
minated video cable for an overall gain of +1 delivered to the
75Ω load. The input video would normally have a level
between 0V to approximately 0.75V.
FIGURE 5. Single Supply Video Driver Capable of
Maintaining Accurate Video Black Level
−
rail. Additional cost savings can be achieved by
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