clc449 National Semiconductor Corporation, clc449 Datasheet - Page 10

• Manufacturer Part Number: clc449
• Description: 1.1ghz Ultra-wideband Monolithic Op Amp
• Manufacturer: National Semiconductor Corporation

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Application Division
DC Design (Output Loading)
R
closed-loop load impedance seen by the output in Figure 5
is:
available output current can produce the required output
voltage swing.
Capacitive Loads
Capacitive loads, such as found in A/D converters, require a
series resistor (R
performance. The R
Typical Performance Characteristics section provides the
information for selecting this resistor.
Also, use a series resistor to reduce the effects of reactive
loads 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 6 shows the typical
circuit configurations for matching transmission lines.
In non-inverting gain applications, R
ground. The resistors R
characteristic impedance
In inverting gain applications, R
ground. The resistor 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
to match the output transmission line over a greater
frequency range. It compensates for the increase of the op
amp’s output impedance with frequency.
L
R
R
R
, R
L_eq
L_eq
L_eq
R
f
eq1
, and R
needs to be kept large enough so that the minimum
= R
= R
FIGURE 6. Transmission Line Matching
L
L
\ (R
\ R
FIGURE 5. DC Offset Model
g
f
load the op amp output. The equivalent
f
R
+R
inverting gain
I
I
s
eq2
BN
s
V
BI
eq2
+
-
in the output to improve settling
and Settling Time vs. C
os
4
), non-inverting gain
1
, R
5
, R
and R
CLC449
+
6
-
2
, and R
, R
6
g
3
, and R
is also equal to Z
(Continued)
is connected directly to
g
7
R
is connected directly to
are equal to Z
f
7
are equal to the
DS012715-35
L
plot in the
R
V
0
L
.
0
o
. The
DS012715-36
6
10
Thermal Design
To calculate the power dissipation for the CLC449, follow
these steps:
To calculate the maximum allowable ambient temperature,
solve the following equation: T
is the thermal resistance from junction to ambient in ˚C/W,
and T
section contains the thermal resistance for various
packages.
Dynamic Range (input/output protection)
Input ESD diodes are present on all connected pins for
protection from static voltage damage. For a signal that 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 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. Inverting gain
applications are limited by the Output Voltage Range.
For transimpedance or inverting gain applications, the
current (I
needs to be:
where V
The voltage ranges discussed above are achieved as long
as the equivalent output load is large enough so that the
output current can produce the required output voltage
swing. See the DC Design (output loading ) sub-section for
details.
Dynamic Range (Intermods)
In RF applications, the CLC449 specifies a third order
intercept of 30dBm at 70MHz and P
10. A2-Tone, 3rd Order IMD Intercept plot is found in the
Typical Performance Characteristics section. The output
power level is taken at the load. Third-order harmonic
distortion is calculated with the formula:
where:
• IP3
• P
• HD3
1. Calculate the no-load op amp power:
P
2. Calculate the output stage’s RMS power:
P
voltage and current across the external load.
3. Calculate the total op amp RMS power:
P
HD3
−dBc.
amp
o
t
O
= P
= (V
amb
rd
O
= output power level, dBm at the load.
rd
= I
max
amp
=Third-order output intercept, dBm at the load.
= 2 x (IP3
inv
cc
cc
= Third-order distortion from the fundamental,
is in ˚C. The Package Thermal Resistance
) injected at the inverting input of the op amp
− V
is the Output Voltage Range .
+ P
(V
cc
load
o
−V
) I
O
EE
load
− P
)
, where V
O
)
amb
= 150 − P
load
O
and I
= 10dBm.at a gain of
load
t
x
are the RMS
JA
where
JA