EL2180C/EL2280C/EL2480C-Preliminary
250MHz / 3mA Current Mode Feedback Amplifiers
output drive of each EL2280C and EL2480C amplifier
n = Number of Amplifiers in the Package
allows swings of ±2.5V into 50W loads.
PDMAX = Maximum Power Dissipation of Each
Amplifier in the Package
Driving Cables and Capacitive Loads
PDMAX for each amplifier can be calculated as follows:
When used as a cable driver, double termination is
always recommended for reflection-free performance.
For those applications, the back-termination series resis-
tor will decouple the EL2180C/EL2280C/EL2480C
from the cable and allow extensive capacitive drive.
However, other applications may have high capacitive
loads without a back-termination resistor. In these appli-
cations, a small series resistor (usually between 5W and
50W) can be placed in series with the output to eliminate
most peaking. The gain resistor (RG) can 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 feed-
back resistor (RF) to reduce the peaking.
V
OUTMAX
PD
= (2 ´ V ´ I
) + (V – V
) ´ ----------------------------
MAX
S
SMAX
S
OUTMAX
R
L
where:
VS = Supply Voltage
ISMAX = Maximum Supply Current of 1 Amplifier
VOUTMAX = Maximum Output Voltage of the
Application
RL = Load Resistance
Current Limiting
The EL2180C/EL2280C/EL2480C have no internal cur-
rent-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
EL2180C/EL2280C/EL2480C, it is possible to exceed
the 150°C Absolute Maximum junction temperature
under certain very high load current conditions. Gener-
ally speaking, when RL falls below about 25W, it is
important to calculate the maximum junction tempera-
ture (TJMAX) for the application to determine if power-
supply voltages, load conditions, or package type need
to be modified for the EL2180C/EL2280C/EL2480C to
remain in the safe operating area. These parameters are
calculated as follows:
T
= T
+ (Q ´ n ´ PD
JA MAX
)
JMAX
MAX
where:
TMAX = Maximum Ambient Temperature
qJA = Thermal Resistance of the Package
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ELANTEC [ ELANTEC SEMICONDUCTOR ]
