el5191cs Intersil Corporation, el5191cs Datasheet - Page 16

• Manufacturer Part Number: el5191cs
• Description: 1ghz Current Feedback Amplifier With Enable
• Manufacturer: Intersil Corporation

As supply voltages continue to decrease, it becomes
necessary to provide input and output voltage ranges that
can get as close as possible to the supply voltages. The
EL5191 has an input range which extends to within 2V of
either supply. So, for example, on ±5V supplies, the EL5191
has an input range which spans ±3V. The output range of the
EL5191 is also quite large, extending to within 1V of the
supply rail. On a ±5V supply, the output is therefore capable
of swinging from -4V to +4V. Single-supply output range is
larger because of the increased negative swing due to the
external pull-down resistor to ground.
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 of the change in output current with DC
level. Previously, good differential gain could only be
achieved by running high idle currents through the output
transistors (to reduce variations in output impedance.)
These currents were typically comparable to the entire 9mA
supply current of each EL5191 amplifier. Special circuitry
has been incorporated in the EL5191 to reduce the variation
of output impedance with current output. This results in dG
and dP specifications of 0.035% and 0.04°, while driving
150Ω at a gain of 2.
Video performance has also been measured with a 500Ω
load at a gain of +1. Under these conditions, the EL5191 has
dG and dP specifications of 0.02% and 0.02°, respectively.
Output Drive Capability
In spite of its low 9mA of supply current, the EL5191 is
capable of providing a minimum of ±95mA of output current.
With a minimum of ±95mA of output drive, the EL5191 is
capable of driving 50Ω loads to both rails, making it an
excellent choice for driving isolation transformers in
telecommunications applications.
Driving Cables and Capacitive Loads
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, the back-termination series resistor will
decouple the EL5191 from the cable and allow extensive
capacitive drive. However, other applications may have high
capacitive loads without a back-termination resistor. In these
applications, a small series resistor (usually between 5Ω and
50Ω) can be placed in series with the output to eliminate
most peaking. The gain resistor (R
make up for any gain loss which may be created by this
additional resistor at the output. In many cases it is also
possible to simply increase the value of the feedback
resistor (R
F
) to reduce the peaking.
16
G
) can then be chosen to
EL5191, EL5191A
Current Limiting
The EL5191 has no internal current-limiting circuitry. If the
output is shorted, it is possible to exceed the Absolute
Maximum Rating for output current or power dissipation,
potentially resulting in the destruction of the device.
Power Dissipation
With the high output drive capability of the EL5191, it is
possible to exceed the +125°C Absolute Maximum junction
temperature under certain very high load current conditions.
Generally speaking when R
important to calculate the maximum junction temperature
(T
voltages, load conditions, or package type need to be
modified for the EL5191 to remain in the safe operating area.
These parameters are calculated as follows:
where:
PD
where:
PD
JMAX
T
θ
n = Number of amplifiers in the package
PD
the package
V
I
V
R
SMAX
MAX
JA
MAX
S
OUTMAX
L
MAX
MAX
= Load resistance
= Supply voltage
= Thermal resistance of the package
) for the application to determine if power supply
for each amplifier can be calculated as follows:
= Maximum ambient temperature
=
= Maximum supply current of 1A
= Maximum power dissipation of each amplifier in
2 (
T
= Maximum output voltage (required)
×
JMAX
V
S
×
I
=
SMAX
T
MAX
)
+
L
+
falls below about 25Ω, it is
(
(
θ
V
JA
S
- V
×
n
OUTMAX
×
PD
MAX
)
)
×
V
--------------------------- -
OUTMAX
May 16, 2007
R
FN7180.3
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