EL5444CSZ datasheet(16/19 Pages) INTERSIL

16 / 19 page

Figure 1 shows the output of the EL5144 series amplifier

swinging rail to rail with RF = 1kΩ, AV = +2 and RL = 1MΩ.

Figure 2 is with RL = 150Ω.

Choice of Feedback Resistor, RF

These amplifiers are optimized for applications that require a

gain of +1. Hence, no feedback resistor is required.

However, for gains greater than +1, the feedback resistor

forms a pole with the input capacitance. As this pole

becomes larger, phase margin is reduced. This causes

ringing in the time domain and peaking in the frequency

domain. Therefore, RF has some maximum value that

should not be exceeded for optimum performance. If a large

value of RF must be used, a small capacitor in the few

picofarad range in parallel with RF can help to reduce this

ringing and peaking at the expense of reducing the

bandwidth.

As far as the output stage of the amplifier is concerned, RF +

RG appear in parallel with RL for gains other than +1. As this

combination gets smaller, the bandwidth falls off.

Consequently, RF also has a minimum value that should not

be exceeded for optimum performance.

For AV = +1, RF = 0Ω is optimum. For AV = -1 or +2 (noise

gain of 2), optimum response is obtained with RF between

300

Ω and 1kΩ. For A

V = -4 or +5 (noise gain of 5), keep RF

between 300

Ω and 15kΩ.

Video Performance

For good video signal integrity, an amplifier is required to

maintain the same output impedance and the same

frequency response as DC levels are changed at the output.

This can be difficult when driving a standard video load of

150

Ω, because of the change in output current with DC level.

A look at the Differential Gain and Differential Phase curves

for various supply and loading conditions will help you obtain

optimal performance. Curves are provided for AV = +1 and

+2, and RL = 150Ω and 10kΩ tied both to ground as well as

2.5V. As with all video amplifiers, there is a common mode

sweet spot for optimum differential gain/differential phase.

For example, with AV = +2 and RL =150Ω tied to 2.5V, and

the output common mode voltage kept between 0.8V and

3.2V, dG/dP is a very low 0.1%/0.1°. This condition

corresponds to driving an AC-coupled, double terminated

Ω coaxial cable. With AV = +1, RL = 150Ω tied to ground,

and the video level kept between 0.85V and 2.95V, these

amplifiers provide dG/dP performance of 0.05%/0.20°. This

condition is representative of using the EL5144 series

amplifier as a buffer driving a DC coupled, double

terminated, 75

Ω coaxial cable. Driving high impedance

loads, such as signals on computer video cards, gives

similar or better dG/dP performance as driving cables.

Driving Cables and Capacitive Loads

The EL5144 series amplifiers can drive 50pF loads in

parallel with 150

Ω with 4dB of peaking and 100pF with 7dB

of peaking. If less peaking is desired in these applications, a

small series resistor (usually between 5

Ω and 50Ω) can be

placed in series with the output to eliminate most peaking.

However, this will obviously reduce the gain slightly. If your

gain is greater than 1, the gain resistor (RG) can then be

chosen to make up for any gain loss which may be created

by this additional resistor at the output. Another method of

reducing peaking is to add a “snubber” circuit at the output. A

snubber is a resistor in a series with a capacitor, 150

Ω and

100pF being typical values. The advantage of a snubber is

that it does not draw DC load current.

When used as a cable driver, double termination is always

recommended for reflection-free performance. For those

applications, the back-termination series resistor will de-

couple the EL5144 series amplifier from the cable and allow

extensive capacitive drive. However, other applications may

have high capacitive loads without a back-termination

resistor. Again, a small series resistor at the output can

reduce peaking.

Disable/Power-Down

The EL5146 and EL5246 amplifiers can be disabled, placing

its output in a high-impedance state. Turn off time is only

10ns and turn on time is around 500ns. When disabled, the

amplifier’s supply current is reduced to 2.6µA typically,

thereby effectively eliminating power consumption. The

amplifier’s power down can be controlled by standard TTL or

CMOS signal levels at the CE pin. The applied logic signal is

FIGURE 1.

FIGURE 2.

EL5144, EL5146, EL5244, EL5246, EL5444

EL5444CSZ Datasheet(PDF) 16 Page - Intersil Corporation

EL5444CSZ Datasheet(HTML) 16 Page - Intersil Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Datasheet Download

Link URL