EL2386

FN7155 Rev 1.00

Page 10 of 13

June 24, 2004

about the same -3dB bandwidth, regardless of closed-loop

gain. However, as closed-loop gain is increased, bandwidth

decreases slightly while stability increases. Since the loop

stability is improving with higher closed-loop gains, it becomes

and still retain stability, resulting in only a slight loss of

bandwidth with increased closed-loop gain.

Supply Voltage Range and Single-Supply Operation

The EL2386 has been designed to operate with supply

voltages having a span of greater than 3V, and less than 12V.

In practical terms, this means that the EL2386 will operate on

dual supplies ranging from ±1.5V to ±6V. With a single-supply,

the EL2386 will operate from +3V to +12V.

As supply voltages continue to decrease, it becomes

necessary to provide input and output voltage ranges that can

get as close as possible to the supply voltages. The EL2386

has an input voltage range that extends to within 1V of either

supply. So, for example, on a single +5V supply, the EL2386

has an input range which spans from 1V to 4V. The output

range of the EL2386 is also quite large, extending to within 1V

of the supply rail. On a ±5V supply, the output is therefore

capable of swinging from -4V to +4V. Single-supply output

range is even larger because of the increased negative swing

due to the external pull-down resistor to ground. On a single

+5V supply, output voltage range is about 0.3V to 4V.

Video Performance

For good video performance, an amplifier is required to

maintain the same output impedance and the same frequency

response as DC levels are changed at the output. This is

especially difficult when driving a standard video load of 150

,

because of the change in output current with DC level. Until the

EL2386, good Differential Gain could only be achieved by

running high idle currents through the output transistors (to

reduce variations in output impedance). These currents were

typically comparable to the entire 3mA supply current of each

EL2386 amplifier! Special circuitry has been incorporated in

the EL2386 to reduce the variation of output impedance with

0.05% and 0.05° while driving 150

 at a gain of +2.

Video Performance has also been measured with a 500

 load

driving 500

For complete curves, see the Differential Gain and Differential

Phase vs Input Voltage curves.

Output Drive Capability

In spite of its low 3mA of supply current per amplifier, the

EL2386 is capable of providing a minimum of ±50mA of output

current. This output drive level is unprecedented in amplifiers

running at these supply currents. With a minimum ±50mA of

output drive, the EL2386 is capable of driving 50

 loads to

±2.5V, making it an excellent choice for driving multiple video

loads in RGB applications.

Driving Cables and Capacitive Loads

When used as a cable driver, double termination is always

recommended for reflection-free performance. For those

applications, the back-termination series resistor will decouple

the EL2386 from the cable and allow extensive capacitive

drive. However, other applications may have high capacitive

loads without a back-termination resistor. In these applications,

a small series resistor (usually between 5

 and 50) can be

placed in series with the output to eliminate most peaking. The

loss which may be created by this additional resistor at the

output. In many cases it is also possible to simply increase the

Current Limiting

The EL2386 has no internal current-limiting circuitry. If an

output is shorted indefinitely, the power dissipation could easily

increase such that the part will be destroyed. Maximum

reliability is maintained if the output current never exceeds

±60mA. A heat sink may be required to keep the junction

temperature below absolute maximum when an output is

shorted indefinitely.

Multiplexing with the EL2386

The ENABLE pins on the EL2386 allow for multiplexing

applications. Figure 1 shows an EL2386 with all 3 outputs tied

together, driving a back terminated 75

 video load. Three sine

waves of varying amplitudes and frequencies are applied to

the three inputs, while a 1 of 3 decoder selects one amplifier to

be on at any given time. Figure 2 shows the resulting output

Notice the outputs are tied directly together. De-coupling

resistors at each output are not required or advised when

multiplexing.

FIGURE 1.