14
FN7328.2
May 3, 2007
Applications Information
Product Description
The EL1516 is a dual voltage feedback operational amplifier
designed especially for DMT ADSL and other applications
requiring very low voltage and current noise. It also features
low distortion while drawing moderately low supply current.
The EL1516 uses a classical voltage-feedback topology
which allows it to be used in a variety of applications where
current-feedback amplifiers are not appropriate because of
restrictions placed upon the feedback element used with the
amplifier. The conventional topology of the EL1516 allows,
for example, a capacitor to be placed in the feedback path,
making it an excellent choice for applications such as active
filters, sample-and-holds, or integrators.
ADSL CPE Applications
The low noise EL1516 amplifier is specifically designed for
the dual differential receiver amplifier function with ADSL
transceiver hybrids as well as other low-noise amplifier
applications. A typical ADSL CPE line interface circuit is
shown in Figure 44. The EL1516 is used in receiving DMT
down stream signal. With careful transceiver hybrid design
and the EL1516 1.4nV/Hz voltage noise and 1.5pA/Hz
current noise performance, -140dBm/Hz system background
noise performance can be easily achieved.
FIGURE 44. TYPICAL LINE INTERFACE CONNECTION
Power Dissipation
With the wide power supply range and large output drive
capability of the EL1516, it is possible to exceed the +150°C
maximum junction temperatures under certain load and
power supply conditions. It is therefore important to calculate
the maximum junction temperature (T
JMAX
) for all
applications to determine if power supply voltages, load
conditions, or package type need to be modified for the
EL1516 to remain in the safe operating area. These
parameters are related as follows:
where:
•PD
MAXTOTAL
is the sum of the maximum power
dissipation of each amplifier in the package (PD
MAX
)
•PD
MAX
for each amplifier can be calculated as follows:
where:
•T
MAX
= Maximum ambient temperature
•
JA
= Thermal resistance of the package
•PD
MAX
= Maximum power dissipation of 1 amplifier
•V
S
= Supply voltage
•I
MAX
= Maximum supply current of 1 amplifier
•V
OUTMAX
= Maximum output voltage swing of the
application
•R
L
= Load resistance
To serve as a guide for the user, we can calculate maximum
allowable supply voltages for the example of the video
cable-driver below since we know that T
JMAX
= +150°C,
T
MAX
= +75°C, I
SMAX
= 7.7mA, and the package
JA
s are
shown in Table 1. If we assume (for this example) that we
are driving a back-terminated video cable, then the
maximum average value (over duty-cycle) of V
OUTMAX
is
1.4V, and R
L
= 150, giving the results seen in Table 1.
Single-Supply Operation
The EL1516 has been designed to have a wide input and
output voltage range. This design also makes the EL1516 an
excellent choice for single-supply operation. Using a single
positive supply, the lower input voltage range is within 1.2V
of ground (R
L
= 500), and the lower output voltage range is
within 875mV of ground. Upper input voltage range reaches
3.6V, and output voltage range reaches 3.8V with a 5V
supply and R
L
= 500. This results in a 2.625V output swing
on a single 5V supply. This wide output voltage range also
allows single-supply operation with a supply voltage as high
as 12V.
-
+
-
+
-
+
-
+
RECEIVE
OUT -
RECEIVE
OUT +
DRIVER
INPUT
R
G
R
F
R
F
R
F
R
R
IN
R
R
IN
R
F
R
OUT
R
OUT
LINE +
RECEIVE
AMPLIFIERS
Z
LINE
-
+
LINE -
TABLE 1.
PART PACKAGE
JA
MAX P
DISS
@
T
MAX
MAX V
S
EL1516IS SO8 110°C/W 0.406W @ +85°C
EL1516IY MSOP8 115°C/W 0.400W @ +85°C
EL1516AIY MSOP10 115°C/W 0.400W @ +85°C
T
JMAX
T
MAX
JA
PD
MAXTOTAL
+=
(EQ. 1)
PD
MAX
2V
S
I
SMAX
V
S
V
OUTMAX
V
OUTMAX
R
L
----------------------------
–+=
(EQ. 2)
EL1516, EL1516A
