el2270 Intersil Corporation, el2270 Datasheet - Page 9

• Manufacturer Part Number: el2270
• Description: 70mhz/1ma Current Mode Feedback Amplifiers
• Manufacturer: Intersil Corporation

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 EL2270, 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 more than the entire 1mA supply
current of each EL2270 amplifier! Special circuitry has been
incorporated in the EL2270 to reduce the variation of output
impedance with current output. This results in dG and dP
specifications of 0.15% and 0.15° whi le 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 EL2270 has
dG and dP specifications of 0.01% and 0.02° respectiv ely
while driving 500: at A
Output Drive Capability
In spite of its low 1mA of supply current, each amplifier of the
EL2270 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 ±50mA minimum output drive of each EL2270
amplifier allows swings of ±2.5V into 50: loads.
V
= +1.
9
EL2270
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 EL2270 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
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 EL2270 has 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 EL2270, it is
possible to exceed the 150°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 EL2270 to remain in the safe operating area.
These parameters are calculated as follows [1]:
where:
PD
where:
T
PD
JMAX
JMAX
T
T
n = Number of amplifiers in the package
PD
the package
V
I
V
R
F
SMAX
MAX
JA
MAX
) to reduce the peaking.
MAX
S
OUTMAX
L
MAX
= Supply voltage
= Load resistance
= Thermal resistance of the package
) for the application to determine if power-supply
=
for each amplifier can be calculated as follows [2]:
= Maximum ambient temperature
=
= Maximum supply current of 1 amplifier
T
= Maximum power dissipation of each amplifier in
2
MAX
= Maximum output voltage of the application
u
V
+
S
u
4
I
JA
SMAX
u
n
u
+
PD
L
V
falls below about 25:, it is
MAX
S
- V
G
OUTMAX
) can then be chosen to
u
V
--------------------------- -
OUTMAX
R
L