Datasheet

Application Notes (Continued)
R
2
should be kept small compared to R
1
in order to not
reduce the ENABLE voltage and to produce little or no delay
to ENABLE.
Other Applications
The LMH6572 may be utilized in systems that involve a
single RGB channel as well whenever there is a need to
switch between different “flavors” of a single RGB input.
Here are some examples:
1. RGB positive polarity, negative polarity switch
2. RGB full resolution, High Pass filter switch
In each of these applications, the same RGB input occupies
one set of inputs to the LMH6572 and the other “flavor”
would be tied to the other input set.
DRIVING CAPACITIVE LOADS
Capacitive output loading applications will benefit from the
use of a series output resistor R
OUT
. Figure 6 shows the use
of a series output resistor, R
OUT
, to stabilize the amplifier
output under capacitive loading. Capacitive loads of
5 to 120 pF are the most critical, causing ringing, frequency
response peaking and possible oscillation. The chart “Sug-
gested R
OUT
vs. Cap Load” gives a recommended value for
selecting a series output resistor for mitigating capacitive
loads. The values suggested in the charts are selected for .5
dB or less of peaking in the frequency response. This gives
a good compromise between settling time and bandwidth.
For applications where maximum frequency response is
needed and some peaking is tolerable, the value of R
OUT
can be reduced slightly from the recommended values.
LAYOUT CONSIDERATIONS
Whenever questions about layout arise, use the evaluation
board as a guide. The LMH730151 is the evaluation board
supplied with samples of the LMH6572. To reduce parasitic
capacitances, ground and power planes should be removed
near the input and output pins. For long signal paths con-
trolled impedance lines should be used, along with imped-
ance matching elements at both ends. Bypass capacitors
should be placed as close to the device as possible. Bypass
capacitors from each rail to ground are applied in pairs. The
larger electrolytic bypass capacitors can be located farther
from the device, the smaller ceramic capacitors should be
placed as close to the device as possible. In Figure 1 and
Figure 2, the capacitor between V
+
and V
−
is optional, but is
recommended for best second harmonic distortion. Another
way to enhance performance is to use pairs of .01 µF and
.1 µF ceramic capacitors for each supply bypass.
20109619
FIGURE 5. Delay Circuit Implementation
20109624
FIGURE 6. Decoupling Capacitive Loads
20109604
FIGURE 7. Recommended R
OUT
vs. Capacitive Load
20109613
FIGURE 8. Frequency Response vs. Capacitive Load
LMH6572
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