LMH6572 datasheet(10/12 Pages) NSC

10 / 12 page

Application Notes (Continued)

2 should be kept small compared to R1 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:

RGB positive polarity, negative polarity switch

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

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