7

The maximum dissipation a package can offer is:

Where

reliability, less to retain optimum electrical performance

and 85°C for industrial range

obtained from data sheet dissipation curves

The more difficult case is the SO-14 package. With a

maximum junction temperature of 150°C and a maximum

ambient temperature of 85°C, the 65°C temperature rise and

package thermal resistance of 120°/W gives a dissipation of

542mW at 85°C. This allows the full maximum operating

supply voltage unloaded, but reduced if loaded significantly.

Output Loading

The output stage is very powerful. It typically can source

85mA and sink 120mA. Of course, this is too much current to

sustain and the part will eventually be destroyed by

excessive dissipation or by metal traces on the die opening.

The metal traces are completely reliable while delivering the

30mA continuous output given in the Absolute Maximum

Ratings table in this data sheet, or higher purely transient

currents.

Gain accuracy degrades only 0.2% from no load to 100

Ω

load. Heavy resistive loading will degrade frequency

response and video distortion for loads < 100

Ω.

Capacitive loads will cause peaking in the frequency

response. If a capacitive load must be driven, a small-valued

series resistor can be used to isolate it. 12

Ω to 51Ω should

suffice. A 22

Ω series resistor will limit peaking to 2.5dB with

even a 220pF load.

Mixer Applications

Because of its lower distortion levels, the Y input is the better

choice for a mixer’s signal port. The X input would receive

oscillator amplitudes of about 1V RMS maximum. Carrier

suppression is initially limited by the offset voltage of the Y

input, 20mV maximum, and is about 37dB worst-case. Better

suppression can be obtained by nulling the offset of the X

input. Similarly, nulling the offset of the Y input will improve

signal-port suppression. Driving an input differentially will

also maximize feedthrough suppression at frequencies

beyond 10MHz.

AC Level Detectors

Square-law converters are commonly used to convert AC

signals to DC voltages corresponding to the original

amplitude in subsystems like automatic gain controls (AGCs)

and amplitude-stabilized oscillators. Due to the controlled AC

amplitudes, the inputs of the multiplier will see a relatively

constant signal level. Best performance will be obtained for

inputs between 200mVRMS and 1VRMS. The traditional use

of the EL4450 as an AGC detector and control loop would

be:

The EL4450 simply provides an output equal to the square

of the input signal and an integrator filters out the AC

component, while comparing the DC component to an

amplitude reference. The integrator output is the DC control

voltage to the variable-gain sections of the AGC (not shown).

If a negative polarity of reference is required, one of the

multiplier input terminal pairs is reversed, inverting the

multiplier output. Input bias current will cause input voltage

offsets due to source impedances; putting a compensating

resistor in series with the grounded inputs of the EL4450 will

reduce this offset greatly.

This control system will attempt to force:

REF

FIGURE 1. TRADITIONAL AGC DETECTOR/DC

FEEDBACK CIRCUIT

EL4450