9

Fade-Control Characteristics

-1

often exceed this range. Actually, the gain transfer function

around -1V and +1V is “soft”, that is, the gain does not clip

to obtain truly 0% or 100%. Because the 0% = or 100%-

extrapolated from two points measured inside the slope of

of -1.5V to +1.5V will assure the full span of numerical

-1

The fade control has a small-signal bandwidth equal to the

about 20ns.

Input Connections

The input transistors can be driven from resistive and

capacitive sources, but are capable of oscillation when

presented with an inductive input. It takes about 80nH of

series inductance to make the inputs actually oscillate,

equivalent to four inches of unshielded wiring or about six

inches of unterminated input transmission line. The

oscillation has a characteristic frequency of 500MHz. Often

placing one’s finger (via a metal probe) or an oscilloscope

probe on the input will kill the oscillation. Normal high

frequency construction obviates any such problems, where

the input source is reasonably close to the fader input. If this

is not possible, one can insert series resistors of around 51

Ω

to de-Q the inputs.

Signal Amplitudes

Signal input common-mode voltage must be between

(V-) + 2.5V and (V+) - 2.5V to ensure linearity. Additionally,

the differential voltage on any input stage must be limited to

±6V to prevent damage. The differential signal range is ±2V

in the EL4453. The input range is substantially constant with

temperature.

The Ground Pin

The ground pin draws only 6µA maximum DC current, and

may be biased anywhere between (V-) +2.5V and

(V+) - 3.5V. The ground pin is connected to the IC’s

substrate and frequency compensation components. It

serves as a shield within the IC and enhances input stage

CMRR and channel-to-channel isolation over frequency, and

if connected to a potential other than ground, it must be

bypassed.

Power Supplies

The EL4453 works well on any supplies from ±3V to ±15V.

The supplies may be of different voltages as long as the

requirements of the GND pin are observed (see the Ground

Pin section for a discussion). The supplies should be

bypassed close to the device with short leads. 4.7µF

tantalum capacitors are very good, and no smaller bypasses

need be placed in parallel. Capacitors as small as 0.01µF

can be used if small load currents flow.

Singe-polarity supplies, such as +12V with +5V can be used,

where the ground pin is connected to +5V and V- to ground.

The inputs and outputs will have to have their levels shifted

above ground to accommodate the lack of negative supply.

The dissipation of the fader increases with power supply

voltage, and this must be compatible with the package

chosen. This is a close estimate for the dissipation of a

circuit:

where

For instance, the EL4453 draws a maximum of 21 mA. With

is 210mW. The maximum supply voltage that the device can

The maximum dissipation a package can offer is:

where

reliability, less to retain optimum electrical performance

and 85°C for industrial range

θ

obtained from datasheet dissipation curves

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

maximum die temperature of 150°C and a maximum

ambient temperature of 70°C, the 80°C temperature rise and

package thermal resistance of 110°/W gives a dissipation of

636mW at 85°C.

This allows ±15V operation over the commercial

temperature range, but higher ambient temperature or output

loading may require lower supply voltages.

Output Loading

The output stage of the EL4453 is very powerful. It typically

can source 80mA 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

EL4453