EL4421 Intersil Corporation, EL4421 Datasheet - Page 9

• Manufacturer Part Number: EL4421
• Description: Multiplexer/Amplifier, Video Mux 2:1, 80MHz, Gain=1, Muxd Dual Input
• Manufacturer: Intersil Corporation

around -2.3V. This will never happen if the input is restricted
to ±2.5V, which is the guaranteed maximum input
compliance with ±5V supplies, and is not a problem with
greater supply voltages. Connecting the feedback network
with a divider will prevent the overloaded output voltage from
being large enough to overload the -input and monotonic
behavior is assured. In any event, keeping signals within
guaranteed compliance limits will assure freedom from
overload problems.
The input and output ranges are substantially constant with
temperature.
Power Supplies
The mux-amps work 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
Switching Characteristics 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.
Single-polarity supplies, such as +12V with +5V can be used
as described in the Switching Characteristics section. The
inputs and outputs will have to have their levels shifted above
ground to accommodate the lack of negative supply.
The dissipation of the mux-amps 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 EL4422 draws a maximum of 14mA and we
might require a 2V peak output into 150Ω and a 270Ω
+270Ω feedback divider. The R
with ±5V supplies is 191mW. The maximum Supply voltage
that the device can run on for a given P
parameter is
The maximum dissipation a package support is
P
I
V
V
R
V
P
S
O
D
S
S
D
PAR
, max is the maximum supply current
, max = (P
, max = (T
is the ± supply voltage (assumed equal)
= 2V
is the output voltage
is the parallel of all resistors loading the output
S
× I
s
D
D
,max + (V
, max-T
+ V
O
2
/R
A
, max)/R
S
PAR
–V
EL4421, EL4422, EL4441, EL4442, EL4443, EL4444
O
)/2I
9
PAR
) × V
S
TH
+ V
is 117Ω. The dissipation
O
/R
O
D
PAR
/R
and the other
PAR
)
Where
The most difficult case is the SO-8 package. With a
maximum die temperature of 150°C and a maximum
ambient temperature of 85°, the 65° temperature rise and
package thermal resistance of 170°/W gives a maximum
dissipation of 382mW. This allows a maximum supply
voltage of ±9.2V for the EL4422 operated in our example. If
the EL4421 were driving a light load (R
operate on ±15V supplies at a 70° maximum ambient.
The EL4441 through EL4444 can operate on ±12V supplies
in the SO package, and all parts can be powered by ±15V
supplies in DIP packages.
Output Loading
The output stage of the mux-amp is very powerful, and 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
Maximum Ratings table in this data sheet, or higher purely
transient currents.
Gain or gain accuracy degrades only 10% from no load to
100Ω load. Heavy resistive loading will degrade frequency
response and video distortion only a bit, becoming
noticeably worse for loads < 100Ω.
Capacitive loads will cause peaking in the frequency
response. If capacitive loads must be driven, a small-valued
series resistor can be used to isolate it. 12Ω to 51Ω should
suffice. A 22Ω series resistor will limit peaking to 2.5dB with
even a 220pF load.
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 6 of
unterminated input transmission line. The oscillation has a
characteristic frequency of 500MHz.
Often simply 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
mux-amp input. If this is not possible, one can insert series
resistors of around 51Ω to de-Q the inputs.
T
reliability, less to retain optimum electrical performance
T
and 85°C for industrial range
R
obtained from data sheet dissipation curves
A
D
TH
, max is the ambient temperature, 70° for commercial
, max is the maximum die temperature, 150°C for
is the thermal resistance of the mounted package,
PAR
→∞), it could