EL1508CL Intersil, EL1508CL Datasheet - Page 13

• Manufacturer Part Number: EL1508CL
• Description: IC LINE DRIVER ADSL 24-QFN
• Manufacturer: Intersil
• Type: Driverr

Specifications of EL1508CL

• Number Of Drivers/receivers: 1/0
• Voltage - Supply: 5 V ~ 12 V
• Mounting Type: Surface Mount
• Package / Case: 24-VQFN Exposed Pad, 24-HVQFN, 24-SQFN, 24-DHVQFN
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Protocol: -

Applications Information
The EL1508 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. The
EL1508 has been optimized as a line driver for ADSL CO
application. The driver output stage has been sized to
provide full ADSL CO power level of 20dBM onto the
telephone lines. Realizing that the actual peak output
voltages and currents vary with the line transformer turns
ratio, the EL1508 is designed to support 450mA of output
current which exceeds the level required for 1:2 transformer
ratio. A typical ADSL interface circuit is shown in Figure 43
below. 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 EL1508 amplifiers are somewhat sensitive to source
impedance. In particular, they do not like being driven by
inductive sources. More than 100nH of source impedance
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 and Dissipation
Due to the high power drive capability of the EL1508, much
attention needs to be paid to power dissipation. The power
that needs to be dissipated in the EL1508 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 EL1508 is not constant with
varying outputs. In reality, 50% of the total quiescent supply
current needed to power each driver is converted in to output
current. Therefore, in the equation below we should subtract
RECEIVE
RECEIVE
DRIVER
DRIVER
INPUT+
INPUT-
OUT +
OUT -
FIGURE 43. TYPICAL LINE INTERFACE CONNECTION
AMPLIFIERS
RECEIVE
2R
G
+
+
-
-
R
R
R
R
+
+
-
-
F
F
F
F
13
R
R
R
R
IN
IN
R
R
OUT
OUT
LINE +
LINE -
Z
LINE
EL1508
the average output current, I
lowest. 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 EL1508 is close to
the maximum available output swing. There is a trade off,
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
Estimating Line Driver Power Dissipation in ADSL
CO Applications
Figure 44 on the following page shows a typical ADSL CO
line driver implementation. The average line power
requirement for the ADSL CO application is 20dBM
(100mW) into a 100Ω line. The average line voltage is
3.16V
factor) of 5.3 implies peak voltage of 16.7V into the line.
Using a differential drive configuration and transformer
coupling with standard back termination, a transformer ratio
of 1:1 is selected. With 1:1 transformer ratio, the impedance
across the driver side of the transformer is 100Ω, the
average voltage is 3.16V
31.6mA. The power dissipated in the EL1508 is a
P
P
Dquiescent
Dquiescent
Dtransistors
V
I
I
V
V
I
S
X
O
S
S
O
is the operating 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
RMS
. The ADSL DMT peak to average ratio (crest
and P
=
=
V
2
S
×
×
Dtransistor
I
(
O
I
O
S
×
–
or 1/2 I
⎛
⎝
21
V
------ - V
2
RMA
S
X
X
–
)
.
O
.
S
S
, or 1/2 I
Q
and the average current is
O
+ to V
+ to V
⎞
⎠
DISS
S
S
) is obtained by adding
S
-)
-)
Q
+ - I
, whichever is the
S
-) / 2
March 26, 2007
FN7014.5