EL5173, EL5373
10
FN7312.10
August 25, 2015
Description of Operation and
Application Information
Product Description
The EL5173 and EL5373 are wide bandwidth, low power and
single/differential ended to differential output amplifiers. They
have a fixed gain of 2. The EL5173 is a single channel
differential amplifier. The EL5373 is a triple channel
differential amplifier. The EL5173 and EL5373 have a -3dB
bandwidth of 450MHz while driving a 200 differential load.
The EL5173 and EL5373 are available with a power-down
feature to reduce the power while the amplifiers are disabled.
Input, Output and Supply Voltage Range
The EL5173 and EL5373 have been designed to operate with a
single supply voltage of 5V to 10V or split supplies with its total
voltage from 5V to 10V. The amplifiers have an input common
mode voltage range from -4.5V to 3.4V for ±5V supply. The
differential mode input range (DMIR) between the two inputs
is from -2.3V to +2.3V. The input voltage range at the REF pin is
from -3.3V to 3.7V. If the input common mode or differential
mode signal is outside the above-specified ranges, it will cause
the output signal to become distorted.
The output of the EL5173 and EL5373 can swing from -3.3V to
3.6V at 200 differential load at ±5V supply. As the load
resistance becomes lower, the output swing is reduced.
Differential and Common Mode Gain
Settings
As shown in the “Simplified Schematic” on page 9, since the
feedback resistors RF and the gain resistor are integrated with
200 and 400, the EL5173 and EL5373 have a fixed gain of
2. The common mode gain is always one.
Driving Capacitive Loads and Cables
The EL5173 and EL5373 can drive 16pF differential capacitor
in parallel with 200 differential load with less than 3.5dB of
peaking. If less peaking is desired in applications, a small
series resistor (usually between 5 to 50) can be placed in
series with each output to eliminate most peaking. However,
this will reduce the gain slightly.
When used as a cable driver, double termination is always
recommended for reflection-free performance. For those
applications, a back-termination series resistor at the
amplifier’s output will isolate the amplifier from the cable and
allow extensive capacitive drive. However, other applications
may have high capacitive loads without a back-termination
resistor. Again, a small series resistor at the output can help to
reduce peaking.
Disable/Power-Down
The EL5173 and EL5373 can be disabled and placed their
outputs in a high impedance state. The turn-off time is about
1.2µs and the turn-on time is about 100ns. When disabled, the
amplifier’s supply current is reduced to 40µA for I
S
+ and
2.5µA for I
S
- typically, thereby effectively eliminating the power
consumption. The amplifier’s power-down can be controlled by
standard CMOS signal levels at the ENABLE pin. The applied
logic signal is relative to V
S
+ pin. Letting the EN pin float or
applying a signal that is less than 1.5V below V
S
+ will enable
the amplifier. The amplifier will be disabled when the signal at
EN
pin is above V
S
+ - 0.5V.
Output Drive Capability
The EL5173 and EL5373 have internal short circuit protection.
Its typical short circuit current is ±55mA. If the output is
shorted indefinitely, the power dissipation could easily
increase such that the part will be destroyed. Maximum
reliability is maintained if the output current never exceeds
±60mA. This limit is set by the design of the internal metal
interconnect.
Power Dissipation
With the high output drive capability of the EL5173 and EL5373,
it is possible to exceed the +125°C absolute maximum junction
temperature under certain load current conditions. Therefore, it
is important to calculate the maximum junction temperature for
the application to determine if the load conditions or package
types need to be modified for the amplifier to remain in the safe
operating area.
The maximum power dissipation allowed in a package is
determined according to Equation 1:
Where:
•T
JMAX
= Maximum junction temperature
•T
AMAX
= Maximum ambient temperature
•
JA
= Thermal resistance of the package
The maximum power dissipation actually produced by an IC is
the total quiescent supply current times the total power supply
voltage, plus the power in the IC due to the load, or as
expressed in Equation 2:
Where:
V
STOT
= Total supply voltage = V
S
+ - V
S
-
I
SMAX
= Maximum quiescent supply current per channel
V
O
= Maximum differential output voltage of the
application
R
LD
= Differential load resistance
I
LOAD
= Load current
i = Number of channels
By setting the two PD
MAX
equations equal to each other, we
can solve the output current and R
LOAD
to avoid the device
overheat.
PD
MAX
T
JMAX
T
AMAX
–
JA
---------------------------------------------
=
(EQ. 1)
(EQ. 2)
PD i V
STOT
I
SMAX
V
STOT
V
O
–
V
O
R
LD
------------
+
=
