CLC446A8B NSC [National Semiconductor], CLC446A8B Datasheet - Page 7

• Manufacturer Part Number: CLC446A8B
• Description: 400MHz, 50mW Current-Feedback Op Amp
• Manufacturer: NSC [National Semiconductor]

Using a resistor in series with a reactive load will also
reduce the load’s effect on amplifier loop dynamics. For
instance, driving coaxial cables without an output series
resistor may cause peaking or oscillation.
Transmission Line Matching
One method for matching the characteristic impedance
of a transmission line is to place the appropriate resistor
at the input or output of the amplifier. Figure 7 shows the
typical circuit configurations for matching transmission
lines.
In non-inverting gain applications, R
directly to ground. The resistors R
are equal to the characteristic impedance, Z
transmission line or cable.
amplifier from reactive loading caused by the transmis-
sion line, or by parasitics.
In inverting gain applications, R
ground. The resistors R
parallel combination of R
The input and output matching resistors attenuate the
signal by a factor of 2, therefore additional gain is needed.
Use C
frequency range. It compensates for the increase of the op
amp’s output impedance with frequency.
Thermal Design
To calculate the power dissipation for the CLC446,
follow these steps:
To calculate the maximum allowable ambient tempera-
ture, solve the following equation: T
where
ambient in °C/W, and T
Thermal Resistance section contains the thermal
resistance for various packages.
Dynamic Range (input /output protection)
ESD diodes are present on all connected pins for
protection from static voltage damage. For a signal that
V
V
1
2
+
+
-
-
1. Calculate the no-load op amp power:
2. Calculate the output stage’s RMS power:
3. Calculate the total op amp RMS power:
6
R
R
to match the output transmission line over a greater
Figure 7: Transmission Line Matching
1
4
P
I
the external load.
P
P
JA
load
o
t
amp
= P
= (V
is the thermal resistance from junction to
are the RMS voltage and current across
= I
amp
Z
Z
0
0
CC
CC
+ P
– V
•
(V
R
R
o
load
R
2
R
5
4
CC
3
g
5
, R
and R
)
amb
– V
6
•
, and R
CLC446
+
-
I
load
EE
R
is in °C.
f
3
g
Use R
)
, where V
is also equal to Z
is connected directly to
7
amb
are equal to Z
C
1
R
6
6
, R
3
g
= 175 – P
2
to isolate the
load
The Package
is connected
, R
Z
0
6
and
, and R
o
, of the
o
o
t
.
. The
•
R
7
JA
V
o
7
,
7
may exceed the supply voltages, we recommend using
diode clamps at the amplifier’s input to limit the signals to
less than the supply voltages.
Dynamic Range (input /output levels)
The Electrical Characteristics section specifies the
Common-Mode Input Range and Output Voltage Range;
these voltage ranges scale with the supplies.
Output Current is also specified in the Electrical
Characteristics section.
Unity gain applications are limited by the Common-Mode
Input Range. At greater non-inverting gains, the Output
Voltage Range becomes the limiting factor.
gain applications are limited by the Output Voltage
Range. For transimpedance gain applications, the sum
of the input currents injected at the inverting
input pin of the op amp needs to be:
where V
Gain (transimpedance) sub-section for details).
The equivalent output load needs to be large enough so
that the minimum output current can produce the
required output voltage swing. See the DC Design (out-
put loading) sub-section for details.
Dynamic Range (noise)
In RF applications, noise is frequently specified as Noise
Figure (NF). This allows the calculation of signal to noise
ratio into a defined load. Figure 8 plots the NF for a
CLC446 at a gain of 10, and with a feedback resistor R
of 100 . The minimum NF (3.9dB) occurs when the
source impedance equals 1600 .
Figure 8: Noise Figure vs. Source Resistance
V
max
s
20
15
10
5
0
+
-
is the Output Voltage Range (see the DC
10
R
R
Figure 9: Noise Model
g
s
100
Source Resistance ( )
i
i
bn 2
bi 2
e
ni 2
1k
CLC446
+
-
R
f
10k
I
in
http://www.national.com
V
100k
R
max
V
f
o
Inverting
,
f