EL2227 Intersil Corporation, EL2227 Datasheet - Page 10

• Manufacturer Part Number: EL2227
• Description: Dual Very Low Noise Amplifier
• Manufacturer: Intersil Corporation

Applications Information
Product Description
The EL2227 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
and is built on Elantec's proprietary high-speed
complementary bipolar process. The EL2227 use a classical
voltage-feedback topology which allows them 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 EL2227 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 EL2227 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 1. The EL2227 is used in receiving DMT
down stream signal. With careful transceiver hybrid design
and the EL2227 1.9nV/√Hz voltage noise and 1.2pA/√Hz
current noise performance, -140dBm/Hz system background
noise performance can be easily achieved.
Disable Function
The EL2227 is in the standard dual amplifier package
without the enable/disable function. A simple way to
implement the enable/disable function is depicted below.
FIGURE 1. TYPICAL LINE INTERFACE CONNECTION
Receive
Receive
Driver
Out +
Input
Out -
Amplifie
Receive
R
G
+
+
-
-
R
R
R
R
+
+
F
F
F
-
-
F
10
R
R
R
R
IN
IN
R
OUT
R
OUT
Line +
Line -
Z
LINE
EL2227
When disabled, both the positive and negative supply
voltages are disconnected (see Figure 2 below.)
Power Dissipation
With the wide power supply range and large output drive
capability of the EL2227, 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
applications to determine if power supply voltages, load
conditions, or package type need to be modified for the
EL2227 to remain in the safe operating area. These
parameters are related as follows:
where:
where:
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
75°C, I
Table 1. If we assume (for this example) that we are driving a
PD
PD
dissipation of each amplifier in the package (PD
PD
T
θ
PD
V
I
V
Application
R
MAX
JA
MAX
S
OUTMAX
L
MAX
MAXTOTAL
MAX
MAX
= Load Resistance
= Supply Voltage
= Thermal Resistance of the Package
SMAX
= Maximum Supply Current of 1 Amplifier
= Maximum Ambient Temperature
=
75k
for each amplifier can be calculated as follows:
= Maximum Power Dissipation of 1 Amplifier
T
2
JMAX
= Maximum Output Voltage Swing of the
= 9.5mA, and the package θ
×
V
is the sum of the maximum power
S
×
=
10k
1k
I
T
SMAX
MAX
FIGURE 2.
1k
1k
10k
+
+
+12V
(
(
θ
V
JA
S
–
+
-
×
V
JMAX
PD
OUTMAX
JMAX
MAXTOTAL
= 150°C, T
JA
1µF
1µF
) for all
)
s are shown in
×
V
--------------------------- -
OUTMAX
)
4.7µF
MAX
R
MAX
L
)
=