9

an excellent choice for applications such as fast log

amplifiers.

Power Dissipation

With the wide power supply range and large output drive

capability of the EL2344, it is possible to exceed the 150°C

maximum junction temperatures under certain load and

power-supply conditions. It is therefore important to calculate

applications to determine if power supply voltages, load

conditions, or package type need to be modified for the

EL2344 to remain in the safe operating area. These

parameters are related as follows:

where PDmaxtotal is the sum of the maximum power

dissipation of each amplifier in the package (PDmax).

PDmax for each amplifier can be calculated as follows:

where:

•

θ

Application

To serve as a guide for the user, we can calculate maximum

allowable supply voltages for the example of the video cable-

shown in Table 1. If we assume (for this example) that we are

driving a back-terminated video cable, then the maximum

Single-Supply Operation

The EL2344 has been designed to have a wide input and

output voltage range. This design also makes the EL2344 an

excellent choice for single-supply operation. Using a single

positive supply, the lower input voltage range is within

range is within 300mV of ground. Upper input voltage range

reaches 4.2V, and output voltage range reaches 3.8V with a

swing on a single 5V supply. This wide output voltage range

also allows single-supply operation with a supply voltage as

high as 36V or as low as 2.5V. On a single 2.5V supply, the

EL2344 still has 1V of output swing.

Gain-Bandwidth Product and the -3dB Bandwidth

The EL2344 has a gain-bandwidth product of 60MHz while

using only 5.2mA of supply current per amplifier. For gains

greater than 4, their closed-loop -3dB bandwidth is

approximately equal to the gain-bandwidth product divided

by the noise gain of the circuit. For gains less than 4, higher-

order poles in the amplifiers’ transfer function contribute to

even higher closed loop bandwidths. For example, the

EL2344 has a -3dB bandwidth of 120MHz at a gain of +1,

dropping to 60MHz at a gain of +2. It is important to note that

the EL2344 has been designed so that this “extra” bandwidth

in low-gain applications does not come at the expense of

stability. As seen in the typical performance curves, the

EL2344 in a gain of +1 only exhibits 1.0dB of peaking with a

1000

Ω load.

Video Performance

An industry-standard method of measuring the video

distortion of components such as the EL2344 is to measure

offset (0IRE) at either 3.58MHz for NTSC or 4.43MHz for

PAL. A second measurement is then made at 0.714V DC

offset (100IRE). Differential gain is a measure of the change

in amplitude of the sine wave, and is measured in percent.

Differential phase is a measure of the change in phase, and

is measured in degrees.

For signal transmission and distribution, a back-terminated

cable (75

Ω in series at the drive end, and 75Ω to ground at

the receiving end) is preferred since the impedance match at

both ends will absorb any reflections. However, when double

termination is used, the received signal is halved; therefore a

gain of 2 configuration is typically used to compensate for

the attenuation.

The EL2344 has been designed as an economical solution

for applications requiring low video distortion. It has been

thoroughly characterized for video performance in the

topology described above, and the results have been

performance curves. In a gain of +2, driving 150

Ω, with

standard video test levels at the input, the EL2344 exhibits

video performance of the EL2344 has been characterized

over the entire DC offset range from -0.714V to +0.714V. For

Input Offset.

TABLE 1

PACKAGE

MAX PDISS

MAX

EL2344CN

PDIP14

70°C/W

1.071W @ 75°C

±11.5V

EL2344CS

SO14

110°C/W

0.682W @ 75°C

±7.5V

EL2344