EL2170C EL2270C EL2470C
70 MHz 1 mA Current Mode Feedback Amplifiers
Applications Information
Contd
Current Limiting
The EL2170C EL2270C EL2470C have no inter-
nal 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 destruc-
tion of the device
Video Performance has also been measured with
a 500X load at a gain of
a
1 Under these condi-
tions the EL2170C EL2270C EL2470C have dG
and dP specifications of 0 01% and 0 02 respec-
tively while driving 500
X
at A
V
e a
1
Output Drive Capability
In spite of its low 1 mA of supply current the
EL2170C is capable of providing a minimum of
g
80 mA of output current Similarly each am-
plifier of the EL2270C and the EL2470C is capa-
ble of providing a minimum of
g
50 mA These
output drive levels are unprecedented in amplifi-
ers running at these supply currents With a min-
imum
g
80 mA of output drive the EL2170C is
capable of driving 50X loads to
g
4V making it
an excellent choice for driving isolation trans-
formers in telecommunications applications
Similarly the
g
50 mA minimum output drive of
each EL2270C and EL2470C amplifier allows
swings of
g
2 5V into 50X loads
Power Dissipation
With the high output drive capability of the
EL2170C EL2270C EL2470C it is possible to
exceed the 150 C Absolute Maximum junction
temperature under certain very high load current
conditions Generally speaking when R
L
falls be-
low about 25X it is important to calculate the
maximum junction temperature (T
JMAX
) for the
application to determine if power-supply volt-
ages load conditions or package type need to be
modified for the EL2170C EL2270C EL2470C to
remain in the safe operating area These parame-
ters are calculated as follows
T
JMAX
e
T
MAX
a
(i
JA
n PD
MAX
)
1
where
T
MAX
i
JA
n
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 EL2170C
EL2270C EL2470C from the cable and allow ex-
tensive capacitive drive However other applica-
tions may have high capacitive loads without a
back-termination resistor In these applications a
small series resistor (usually between 5X and
50X) can be placed in series with the output to
eliminate most peaking The gain resistor (R
G
)
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 feedback resistor
(R
F
) to reduce the peaking
e
Maximum Ambient Temperature
e
Thermal Resistance of the Package
e
Number of Amplifiers in the Pack-
age
PD
MAX
e
Maximum Power Dissipation of
Each Amplifier in the Package
PD
MAX
for each amplifier can be calculated as
follows
PD
MAX
e
(2 V
S
I
SMAX
)
a
(V
S
b
V
OUTMAX
) (V
OUTMAX
R
L
))
2
where
V
S
I
SMAX
e
Supply Voltage
e
Maximum Supply Current of 1
Amplifier
V
OUTMAX
e
Max Output Voltage of the Ap-
plication
e
Load Resistance
R
L
12
ELANTEC [ ELANTEC SEMICONDUCTOR ]
