EL4453C
Video Fader
Fade-Control Characteristics
The quantity V
The Ground Pin
The ground pin draws only 6 mA maximum DC
current, and may be biased anywhere between
in the above equations is
FADE
s
s
externally applied voltages often exceed this
b
bounded as
1
V
FADE
1, even though the
b
a
a b
(V
)
2.5V and (V ) 3.5V. The ground pin
range. Actually, the gain transfer function
a
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.
b
around 1V and 1V is ‘‘soft’’, that is, the gain
does not clip abruptly below the 0%-V volt-
FADE
level. An over-
age or above the 100%–V
drive of 0.3V must be applied to V
FADE
to obtain
or 100%-
levels cannot be precisely determined,
FADE
e
truly 0% or 100%. Because the 0%
V
FADE
they are extrapolated from two points measured
inside the slope of the gain transfer curve. Gener-
Power Supplies
The EL4453C works well on any supplies from
b
a
ally, an applied V
range of 1.5V to 1.5V
1
s
F 1.
FADE
will assure the full span of numerical
g
g
3V to 15V. The supplies may be of different
b
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. 4.7 mF tanta-
lum capacitors are very good, and no smaller by-
passes need be placed in parallel. Capacitors as
small as 0.01 mF can be used if small load cur-
rents flow.
s
s
s
V
FADE
1 and 0
The fade control has a small-signal bandwidth
equal to the V channel bandwidth, and over-
load recovery resolves in about 20 ns.
IN
Input Connections
The input transistors can be driven from resistive
and capacitive sources, but are capable of oscilla-
tion when presented with an inductive input. It
takes about 80 nH 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 oscil-
lation has a characteristic frequency of 500 MHz.
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 51X to de-Q the inputs.
a
a
Singe-polarity supplies, such as 12V with 5V
can be used, where the ground pin is connected to
a
b
5V and V to ground. The inputs and outputs
will have to have their levels shifted above
ground to accommodate the lack of negative sup-
ply.
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:
e
c
c
a
b
V ) V /R
PAR
c
P
D
2
V , max
S
V
S
(V
S
O O
where I , max is the maximum supply current
S
g
supply voltage
V
is the
S
(assumed equal)
Signal Amplitudes
Signal input common-mode voltage must be be-
V
R
is the output voltage
O
is the parallel of all resistors
PAR
loading the output
b
a
a
linearity. Additionally, the differential voltage on
b
2.5V to ensure
tween (V
)
2.5V and (V
)
g
any input stage must be limited to 6V to pre-
vent damage. The differential signal range is
g
2V in the EL4453C. The input range is sub-
stantially constant with temperature.
10
ELANTEC [ ELANTEC SEMICONDUCTOR ]
