el8203 Intersil Corporation, el8203 Datasheet - Page 11

• Manufacturer Part Number: el8203
• Description: 500mhz Rail-to-rail Amplifiers
• Manufacturer: Intersil Corporation

Choice of Feedback Resistor and Gain Bandwidth
Product
For applications that require a gain of +1, no feedback
resistor is required. Just short the output pin to the inverting
input pin. For gains greater than +1, the feedback resistor
forms a pole with the parasitic capacitance at the inverting
input. As this pole becomes smaller, the amplifier’s phase
margin is reduced. This causes ringing in the time domain
and peaking in the frequency domain. Therefore, R
some maximum value that should not be exceeded for
optimum performance. If a large value of R
small capacitor in the few pF range in parallel with R
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
appear in parallel with R
combination gets smaller, the bandwidth falls off.
Consequently, R
be exceeded for optimum performance. For gain of +1, R
is optimum. For the gains other than +1, optimum response
is obtained with R
The EL8202, EL8203 and EL8403 have a gain bandwidth
product of 200MHz. For gains ≥5, its bandwidth can be
predicted by the following equation:
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 EL8202,
EL8203 and EL8403 to reduce the variation of the output
impedance with the current output. This results in dG and dP
specifications of 0.01% and 0.01°, while driving 150Ω at a
gain of 2. Driving high impedance loads would give a similar
or better dG and dP performance.
Driving Capacitive Loads and Cables
The EL8202, EL8203 and EL8403 can drive 5pF 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
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
Gain
×
BW
=
200MHz
F
F
G
also has a minimum value that should not
between 300Ω to 1kΩ.
can then be chosen to make up for any
L
for gains other than +1. As this
11
F
must be used, a
EL8202, EL8203, EL8403
F
and R
F
F
has
can
F
G
=0
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.
Disable/Power-Down
The EL8202 can be disabled and placed its output in a high
impedance state. The turn off time is about 25ns and the turn
on time is about 200ns. When disabled, the amplifier’s
supply current is reduced to 40µA 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
applying a signal that is less than 0.8V above V
the amplifier. The amplifier will be disabled when the signal
at ENABLE pin is 2V above V
Output Drive Capability
The EL8202, EL8203 and EL8403 do not have internal short
circuit protection circuitry. They have a typical short circuit
current of 80mA sourcing and 150mA 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.
Power Dissipation
With the high output drive capability of the EL8202, EL8203
and EL8403. 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:
Where:
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:
PD
T
T
θ
MAX
JA
AMAX
JMAX
= Thermal resistance of the package
=
= Maximum junction temperature
T
-------------------------------------------- -
= Maximum ambient temperature
JMAX
θ
–
JA
T
AMAX
S
- pin. Letting the ENABLE pin float or
S
-.
S
- will enable