EL2280 Intersil Corporation, EL2280 Datasheet - Page 12

• Manufacturer Part Number: EL2280
• Description: 250MHz/3mA Current Mode Feedback Amplifiers
• Manufacturer: Intersil Corporation

Supply Voltage Range and Single-Supply
Operation
The EL2180, EL2280, and EL2480 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
EL2180, EL2280, and EL2480 will operate on dual supplies
ranging from ±1.5V to ±6V. With a single-supply, the EL2180,
EL2280, and EL2480 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
EL2180, EL2280, and EL2480 have an input voltage range
that extends to within 1V of either supply. So, for example, on
a single +5V supply, the EL2180, EL2280, and EL2480 have
an input range which spans from 1V to 4V. The output range
of the EL2180, EL2280, and EL2480 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 150Ω, because of the change in output current with DC
level. Until the EL2180, EL2280, and EL2480, 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 supply current of each
EL2180, EL2280, and EL2480 amplifier! Special circuitry
has been incorporated in the EL2180, EL2280, and EL2480
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 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 EL2180,
EL2280, and EL2480 have dG and dP specifications of
0.01% and 0.01° respectively while driving 500Ω at A
Output Drive Capability
In spite of its low 3mA of supply current, the EL2180 is
capable of providing a minimum of ±80mA of output current.
Similarly, each amplifier of the EL2280 and the EL2480 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 EL2180
is capable of driving 50Ω loads to ±4V, making it an excellent
choice for driving isolation transformers in
telecommunications applications. Similarly, the ±50mA
12
EL2180, EL2280, EL2480
V
= +1.
minimum output drive of each EL2280 and EL2480 amplifier
allows swings of ±2.5V into 50Ω 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 EL2180, EL2280, and EL2480 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
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 EL2180, EL2280, and EL2480 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 EL2180, EL2280,
and EL2480, it is possible to exceed the 150°C Absolute
Maximum junction temperature under certain very high load
current conditions. Generally speaking, when R
about 25Ω, it is important to calculate the maximum junction
temperature (T
supply voltages, load conditions, or package type need to be
modified for the EL2180, EL2280, and EL2480 to remain in
the safe operating area. These parameters are calculated as
follows [1]:
where:
PD
where:
PD
T
θ
n = Number of amplifiers in the package
PD
the package
V
I
V
R
F
SMAX
MAX
JA
) to reduce the peaking.
MAX
S
OUTMAX
L
MAX
MAX
= Load resistance
= Supply voltage
= Thermal resistance of the package
for each amplifier can be calculated as follows [2]:
= Maximum ambient temperature
= Maximum supply current of 1 amplifier
=
= Maximum power dissipation of each amplifier in
T
JMAX
2 (
= Maximum output voltage of the application
JMAX
×
V
=
S
×
) for the application to determine if power-
T
I
MAX
SMAX
+
)
(
Θ
+
JA
(
V
S
×
n
- V
×
OUTMAX
PD
MAX
G
)
) can then be
)
L
×
falls below
V
--------------------------- -
OUTMAX
R
L