clc451 National Semiconductor Corporation, clc451 Datasheet - Page 7

• Manufacturer Part Number: clc451
• Description: Single Supply, Low-power, High Output, Programmable Buffer
• Manufacturer: National Semiconductor Corporation

The CLC451 is a current feedback buffer built in an
advanced complementary bipolar process. The CLC451
operates from a single 5V supply or dual ±5V supplies.
Operating from a single 5V supply, the CLC451 has the
following features:
The CLC451 performance is further enhanced in ±5V
supply applications as indicated in the ±5V Electrical
Characteristics table and ±5V Typical Performance plots.
If gains other than +1, -1, or +2V/V are required, then the
CLC450 can be used. The CLC450 is a current feedback
amplifier with near identical performance and allows for
external feedback and gain setting resistors.
Current Feedback Amplifiers
Some of the key features of current feedback technology are:
Closed Loop Gain Selection
The CLC451 is a current feedback op amp with
R
three closed loop gains without using any external gain or
feedback resistors. Implement gains of +2, +1, and
-1V/V by connecting pins 2 and 3 as described in the
chart below.
The gain accuracy of the CLC451 is excellent and
stable over temperature change.
setting resistors, R
with a process variation of ± 20% and a temperature
coefficient of ˜ 2000ppm/°C .
values change with processing and temperature, their
ratio (R
used in series with R
will suffer.
f
= R
+1V/V
+2V/V
-1V/V
Gain
A
g
Gains of +1, -1, and 2V/V are achievable without
external resistors
Provides 100mA of output current while
consuming only 7.5mW of power
Offers low -66/-75dBc 2nd and 3rd harmonic
distortion
Provides BW > 60MHz and 1MHz distortion
< -55dBc at V
Independence of AC bandwidth and voltage gain
Inherently stable at unity gain
Adjustable frequency response with feedback resistor
High slew rate
Fast settling
v
f
/R
= 1k
g
) remains constant. If an external resistor is
Non-Inverting (pin3)
on chip (in the package). Select from
input signal
input signal
f
and R
o
ground
g
= 2V
, gain accuracy over temperature
Input Connections
g
pp
are diffused silicon resistors
Although their absolute
CLC451 Design Information
The internal gain
Inverting (pin2)
input signal
NC (open)
ground
CLC451 Operation
7
Current feedback operation can be described using a simple
equation. The voltage gain for a non-inverting or inverting
current feedback amplifier is approximated by Equation 1.
where:
The denominator of Equation 1 is approximately equal to
1 at low frequencies. Near the -3dB corner frequency, the
interaction between R
performance. The value of the feedback resistor has a
large affect on the circuits performance. Increasing R
has the following affects:
Single Supply Operation (V
The specifications given in the +5V Electrical Character-
istics table for single supply operation are measured with
a common mode voltage (V
age around which the inputs are applied and the
output voltages are specified.
Operating from a single +5V supply, the Common Mode
Input Range (CMIR) of the CLC451 is typically +0.8V to
+4.2V. The typical output range with R
to +4.0V.
For single supply DC coupled operation, keep input
signal levels above 0.8V DC. For input signals that drop
below 0.8V DC, AC coupling and level shifting the signal
are recommended. The non-inverting and inverting
configurations for both input conditions are illustrated in
the following 2 sections.
DC Coupled Single Supply Operation
Figures 1, 2, and 3 on the following page, show the
recommended configurations for input signals that
remain above 0.8V DC.
V
V
in
o
A
R
Z(j ) is the CLC451’s open loop transimpedance
gain
Decreases loop gain
Decreases bandwidth
Reduces gain peaking
Lowers pulse response overshoot
Affects frequency response phase linearity
Z j
v
f
R
1
is the feedback resistor
is the closed loop DC voltage gain
f
A
Z(j )
R
v
is the loop gain
f
f
and Z(j ) dominates the circuit
Equation 1
cm
CC
) of 2.5V. V
= +5V, V
L
http://www.national.com
=100
EE
cm
= GND)
is the volt-
is +1.0V
f