el1503a Intersil Corporation, el1503a Datasheet - Page 13

• Manufacturer Part Number: el1503a
• Description: High Power Differential Line Driver
• Manufacturer: Intersil Corporation

Applications Information
The EL1503A consists of two high-power line driver
amplifiers that can be connected for full duplex differential
line transmission. The amplifiers are designed to be used
with signals up to 4MHz and produce low distortion levels. A
typical interface circuit is shown in Figure 39 below.
The amplifiers are wired with one in positive gain and the
other in a negative gain configuration to generate a
differential output for a single-ended input. They will exhibit
very similar frequency responses for gains of three or
greater and thus generate very small common-mode outputs
over frequency, but for low gains the two drivers R
to be adjusted to give similar frequency responses. The
positive-gain driver will generally exhibit more bandwidth and
peaking than the negative-gain driver.
If a differential signal is available to the drive amplifiers, they
may be wired so:
Each amplifier has identical positive gain connections, and
optimum common-mode rejection occurs. Further, DC input
errors are duplicated and create common-mode rather than
differential line errors.
Input Connections
The EL1503A amplifiers are somewhat sensitive to source
impedance. In particular, they do not like being driven by
inductive sources. More than 100nH of source impedance
RECEIVE
RECEIVE
FIGURE 40. DRIVERS WIRED FOR DIFFERENTIAL INPUT
DRIVER
FIGURE 39. TYPICAL LINE INTERFACE CONNECTION
OUT +
INPUT
OUT -
AMPLIFIERS
RECEIVE
R
G
2R
+
+
-
-
R
R
R
R
G
+
+
F
F
F
-
-
F
+
+
-
-
13
R
R
R
R
F
F
R
R
IN
IN
R
R
OUT
OUT
LINE +
F
's need
LINE -
Z
LINE
EL1503A
can cause ringing or even oscillations. This inductance is
equivalent to about 4” of unshielded wiring, or 6” of
unterminated transmission line. Normal high-frequency
construction obviates any such problem.
Power Supplies & Dissipation
Due to the high power drive capability of the EL1503A, much
attention needs to be paid to power dissipation. The power
that needs to be dissipated in the EL1503A has two main
contributors. The first is the quiescent current dissipation.
The second is the dissipation of the output stage.
The quiescent power in the EL1503A is not constant with
varying outputs. In reality, 7mA of the 12.5mA needed to
power each driver is converted in to output current.
Therefore, in the equation below we should subtract the
average output current, I
We’ll call this term I
Therefore, we can determine a quiescent current with the
equation:
where:
The dissipation in the output stage has two main
contributors. Firstly, we have the average voltage drop
across the output transistor and secondly, the average
output current. For minimal power dissipation, the user
should select the supply voltage and the line transformer
ratio accordingly. The supply voltage should be kept as low
as possible, while the transformer ratio should be selected
so that the peak voltage required from the EL1503A is close
to the maximum available output swing. There is a trade of
however with the selection of transformer ratio. As the ratio
is increased, the receive signal available to the receivers is
reduced.
Once the user has selected the transformer ratio, the
dissipation in the output stages can be selected with the
following equation:
where:
The overall power dissipation (P
P
P
P
Dquiescent
Dquiescent
Dtransistors
V
I
I
V
V
I
S
X
O
S
S
O
is the maximum quiescent supply current (I
is the lesser of I
is the average output current per channel
is the supply voltage (V
is the supply voltage (V
is the average output voltage per channel
and P
=
=
V
2
S
×
×
Dtransistor
I
X
(
O
I
O
.
S
×
–
or 7mA (generally I
⎛
⎝
2I
V
------ -
O
2
S
X
, or 7mA, whichever is the lowest.
)
–
.
V
S
S
O
+ to V
+ to V
⎞
⎠
DISS
S
S
) is obtained by adding
-)
-)
X
= 7mA)
S
+ + I
March 26, 2007
FN7039.2
S
-)