LMH6601_09 Datasheet, PDF (18/28 Pages) National Semiconductor (TI) – 250 MHz, 2.4V CMOS Operational Amplifier with Shutdown

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:
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FIGURE 3. LMH6601 Output Overload Recovery
Waveform
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 re-
covery 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⁺ rail, the output does not experience output phase
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 oth-
ers. 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.
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
− _{rail. Additional cost savings can be achieved by eliminating}
or reducing the value of the input and output AC coupling ca-
pacitors commonly employed in single supply video applica-
tions. 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 in-
terest when operating in a low voltage single supply environ-
ment. 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 buffered by the
LMH6601 which then drives the 75Ω back terminated video
cable for an overall gain of +1 delivered to the 75Ω load. The
input video would normally have a level between 0V to ap-
proximately 0.75V.
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FIGURE 4. LMH6601’s “Clean” Swing to Either Rail
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FIGURE 5. Single Supply Video Driver Capable of
Maintaining Accurate Video Black Level
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