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EL2176CEL2276C
70 MHz1 mA Current Mode Feedback Amp wDisable
Applications Information
Contd
entire 1 mA supply current of each EL2176C
EL2276C amplifier Special circuitry has been in-
corporated in the EL2176CEL2276C to reduce
the variation of output impedance with current
output This results in dG and dP specifications
of 015% and 015 while driving 150
X at a gain
of a2
Video Performance has also been measured with
a 500
X load at a gain of a1 Under these condi-
tions the EL2176CEL2276C have dG and dP
specifications of 001% and 002
respectively
while driving 500
X at AV ea1
Output Drive Capability
In spite of its low 1 mA of supply current the
EL2176C is capable of providing a minimum of
g
80 mA of output current Similarly each am-
plifier of the EL2276C is capable of providing a
minimum of g50 mA These output drive levels
are unprecedented in amplifiers running at these
supply currents With a minimum g80 mA of
output drive the EL2176C is capable of driving
50
X loads to g4V making it an excellent choice
for driving isolation transformers in telecommu-
nications applications Similarly the g50 mA
minimum output drive of each EL2276C amplifi-
er allows swings of g25V into 50
X loads
Driving Cables and Capacitive Loads
When used as a cable driver double termination
is always recommended for reflection-free per-
formance For those applications the back-termi-
nation series resistor will decouple the EL2176C
EL2276C from the cable and allow extensive ca-
pacitive drive However other applications may
have high capacitive loads without a back-termi-
nation resistor In these applications a small se-
ries resistor (usually between 5
X and 50X) can be
placed in series with the output to eliminate most
peaking The gain resistor (RG) can then be cho-
sen 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 in-
crease the value of the feedback resistor (RF)to
reduce the peaking
Current Limiting
The EL2176CEL2276C 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 de-
vice
Power Dissipation
With the high output drive capability of the
EL2176CEL2276C it is possible to exceed the
150 C Absolute Maximum junction temperature
under certain very high load current conditions
Generally speaking when RL falls below about
25
X it is important to calculate the maximum
junction temperatu re (TJmax) for the application
to determine if power-supply voltages load con-
ditions or package type need to be modified for
the EL2176CEL2276C to remain in the safe op-
erating area These parameters are calculated as
follows
TJMAX e TMAX a (iJA n PDMAX)
1
where
TMAX
e
Maximum Ambient Temperature
iJA
e
Thermal Resistance of the Package
n
e
Number of Amplifiers in the Pack-
age
PDMAX e Maximum Power Dissipation of
Each Amplifier in the Package
PDMAX for each amplifier can be calculated as
follows
PDMAX e (2 VS ISMAX) a
(VS b VOUTMAX) (VOUTMAX RL))
2
where
VS
e
Supply Voltage
ISMAX
e
Maximum Supply Current of 1
Amplifier
VOUTMAX e Max Output Voltage of the Ap-
plication
RL
e
Load Resistance
12