el2286cn Intersil Corporation, el2286cn Datasheet - Page 10

• Manufacturer Part Number: el2286cn
• Description: 250mhz/3ma Current Mode Feedback Amp W/disable
• Manufacturer: Intersil Corporation

Feedback Resistor Values
The EL2186/EL2286 have been designed and specified at
gains of +1 and +2 with R
resistor gives 250MHz of -3dB bandwidth at A
about 2.5dB of peaking, and 180MHz of -3dB bandwidth at
A
EL2186/EL2286 are current-feedback amplifiers, it is also
possible to change the value of R
As seen in the curve of Frequency Response For Various R
and R
varying the value of the feedback resistor.
Because the EL2186/EL2286 are current-feedback
amplifiers, their gain-bandwidth product is not a constant for
different closed-loop gains. This feature actually allows the
EL2186/EL2286 to maintain about the same -3dB
bandwidth, regardless of closed-loop gain. However, as
closed-loop gain is increased, bandwidth decreases slightly
while stability increases.
Since the loop stability is improving with higher closed-loop
gains, it becomes possible to reduce the value of R
the specified 750: and still retain stability, resulting in only a
slight loss of bandwidth with increased closed-loop gain.
Supply Voltage Range and Single-Supply
Operation
The EL2186/EL2286 have been designed to operate with
supply voltages having a span of greater than 3V, and less
than 12V. In practical terms, this means that the
EL2186/EL2286 will operate on dual supplies ranging from
±1.5V to ±6V. With a single-supply, the EL2176 will operate
from +3V to +12V.
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
EL2186/EL2286 have an input voltage range that extends to
within 1V of either supply. So, for example, on a single +5V
supply, the EL2186/EL2286 have an input range which
spans from 1V to 4V. The output range of the
EL2186/EL2286 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 even larger because of the increased negative
swing due to the external pull-down resistor to ground. On a
single +5V supply, output voltage range is about 0.3V to 4V.
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 150:, because of the change in output current with DC
level. Until the EL2186/EL2286, 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 3mA
V
= +2 with about 0.1dB of peaking. Since the
G
, bandwidth and peaking can be easily modified by
F
= 750:. This value of feedback
10
F
to get more bandwidth.
V
= +1 with
F
below
EL2186, EL2286
F
supply current of each EL2186/EL2286 amplifier! Special
circuitry has been incorporated in the EL2186/EL2286 to
reduce the variation of output impedance with current output.
This results in dG and dP specifications of 0.05% and 0.05°
while driving 150: at a gain of +2.
Video Performance has also been measured with a 500:
load at a gain of +1. Under these conditions, the
EL2186/EL2286 have dG and dP specifications of 0.01%
and 0.01° re spectively while driving 500: at A
Output Drive Capability
In spite of its low 3mA of supply current, the EL2186 is
capable of providing a minimum of ±80mA of output current.
Similarly, each amplifier of the EL2286 is capable of
providing a minimum of ±50mA. These output drive levels
are unprecedented in amplifiers running at these supply
currents. With a minimum ±80mA of output drive, the
EL2186 is capable of driving 50: loads to ±4V, making it an
excellent choice for driving isolation transformers in
telecommunications applications. Similarly, the ±50mA
minimum output drive of each EL2286 amplifier allows
swings of ±2.5V into 50: loads.
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 EL2186/EL2286 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 5: and 50:) can be placed in series with the
output to eliminate most peaking. The gain resistor (R
then be chosen to 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
Current Limiting
The EL2186/EL2286 have no internal current-limiting
circuitry. If any output is shorted, it is possible to exceed the
Absolute Maximum Ratings for output current or power
dissipation, potentially resulting in the destruction of the
device.
Power Dissipation
With the high output drive capability of the EL2186/EL2286,
it is possible to exceed the 150°C Ab solute Maximum
junction temperature under certain very high load current
conditions. Generally speaking, when R
25:, it is important to calculate the maximum junction
temperature (T
power-supply voltages, load conditions, or package type
need to be modified for the EL2186/EL2286 to remain in the
safe operating area. These parameters are calculated as
follows:
Jmax
) for the application to determine if
F
) to reduce the peaking.
L
falls below about
V
= +1.
G
) can