el2480 Intersil Corporation, el2480 Datasheet - Page 10

• Manufacturer Part Number: el2480
• Description: 250mhz/3ma Current Mode Feedback Amplifiers
• Manufacturer: Intersil Corporation

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 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 EL2480 amplifier! Special circuitry has been
incorporated in the 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 EL2480 has
dG and dP specifications of 0.01% and 0.01° respectively
while driving 500Ω at A
Output Drive Capability
This amplifier of the EL2480 is capable of providing a
minimum of ±50mA. These output drive levels are
unprecedented in amplifiers running at these supply currents.
The ±50mA minimum output drive of the 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 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
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
reduce the peaking.
Current Limiting
The EL2480 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 EL2480, 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
JMAX
) for the application to determine if power-supply
V
= +1.
L
G
10
falls below about 25Ω, it is
) can then be chosen to make
F
) to
EL2480
modified for the EL2480 to remain in the safe operating area.
These parameters are calculated as follows:
where:
PD
where:
PD
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 each amplifier can be calculated as follows:
= 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
×
V
=
S
×
T
I
MAX
SMAX
+
)
(
Θ
+
JA
(
V
S
×
n
- V
×
OUTMAX
PD
MAX
)
)
×
V
--------------------------- -
OUTMAX
R
L