EL8100, EL8101
and peaking in the frequency domain. Therefore, R
F
has
some maximum value that should not be exceeded for
optimum performance. If a large value of R
F
must be used, a
small capacitor in the few Pico farad range in parallel with R
F
can help to reduce the ringing and peaking at the expense of
reducing the bandwidth.
As far as the output stage of the amplifier is concerned, the
output stage is also a gain stage with the load. R
F
and R
G
appear in parallel with R
L
for gains other than +1. As this
combination gets smaller, the bandwidth falls off.
Consequently, R
F
also has a minimum value that should not
be exceeded for optimum performance. For gain of +1,
R
F
= 0 is optimum. For the gains other than +1, optimum
response is obtained with R
F
between 300Ω to 1kΩ.
The EL8100, EL8101 have a gain bandwidth product of
100MHz. For gains
≥5,
its bandwidth can be predicted by
Equation 1:
Gain
×
BW
=
100MHz
(EQ. 1)
turn-on time is about 200ns. When disabled, the amplifier’s
supply current is reduced to 30µA typically, thereby
effectively eliminating the power consumption. The
amplifier’s power-down can be controlled by standard TTL or
CMOS signal levels at the ENABLE pin. The applied logic
signal is relative to V
S
- pin. Letting the ENABLE pin float or
applying a signal that is less than 0.8V above V
S
- will enable
the amplifier. The amplifier will be disabled when the signal
at the ENABLE pin is 2V above V
S
-.
Output Drive Capability
The EL8100, EL8101 do not have internal short circuit
protection circuitry. They have a typical short circuit current
of 70mA sourcing and 140mA sinking for the output is
connected to half way between the rails with a 10Ω resistor.
If the output is shorted indefinitely, the power dissipation
could easily increase such that the part will be destroyed.
Maximum reliability is maintained if the output current never
exceeds ±40mA. This limit is set by the design of the internal
metal interconnections.
Video Performance
For good video performance, an amplifier is required to
maintain the same output impedance and the same
frequency response as DC levels are changed at the output.
This is especially difficult when driving a standard video load
of 150Ω, because the change in output current with DC level.
Special circuitry has been incorporated in the
EL8100, EL8101 to reduce the variation of the output
impedance with the current output. This results in dG and dP
specifications of 0.03% and 0.05°, while driving 150Ω at a
gain of 2. Driving high impedance loads would give a similar
or better dG and dP performance.
Power Dissipation
With the high output drive capability of the EL8100, EL8101,
it is possible to exceed the +125°C absolute maximum
junction temperature under certain load current conditions.
Therefore, it is important to calculate the maximum junction
temperature for the application to determine if the load
conditions or package types need to be modified for the
amplifier to remain in the safe operating area.
The maximum power dissipation allowed in a package is
determined according to Equation 2:
T
JMAX
–
T
AMAX
-
PD
MAX
= --------------------------------------------
θ
JA
(EQ. 2)
Driving Capacitive Loads and Cables
The EL8100, EL8101 can drive 15pF loads in parallel with
1kΩ with less than 5dB of peaking at gain of +1. If less
peaking is desired in applications, a small series resistor
(usually between 5Ω to 50Ω) can be placed in series with the
output to eliminate most peaking. However, this will reduce
the gain slightly. If the gain setting is greater than 1, the gain
resistor R
G
can then be chosen to make up for any gain loss
which may be created by the additional series resistor at the
output.
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, a back-termination series resistor at the
amplifier’s output will isolate the amplifier from the cable and
allow extensive capacitive drive. However, other applications
may have high capacitive loads without a back-termination
resistor. Again, a small series resistor at the output can help
to reduce peaking.
Where:
T
JMAX
= Maximum junction temperature
T
AMAX
= Maximum ambient temperature
θ
JA
= Thermal resistance of the package
The maximum power dissipation actually produced by an IC
is the total quiescent supply current times the total power
supply voltage, plus the power in the IC due to the load, or:
For sourcing, Equation 3:
V
OUT
-
PD
MAX
=
V
S
×
I
SMAX
+
(
V
S
–
V
OUT
) ×
---------------
R
L
(EQ. 3)
For sinking, Equation 4:
PD
MAX
=
V
S
×
I
SMAX
+
(
V
OUT
–
V
S
-
) ×
I
LOAD
(EQ. 4)
Where:
V
S
= Total supply voltage
I
SMAX
= Maximum quiescent supply current
Disable/Power-Down
The EL8100 can be disabled and placed its output in a high
impedance state. The turn-off time is about 25ns and the
9
FN7103.9
September 14, 2010
INTERSIL [ INTERSIL CORPORATION ]
