CLC450 Datasheet, PDF (8/12 Pages) National Semiconductor (TI) – Single Supply, Low-Power, High Output, Current Feedback Amplifier

AC Coupled Single Supply Operation
Figures 3 and 4 show possible non-inverting and invert-
ing configurations for input signals that go below 0.8V
DC. The input is AC coupled to prevent the need for
level shifting the input signal at the source. The resistive
voltage divider biases the non-inverting input to V_CC ÷ 2
= 2.5V (For V_CC = +5V).
VCC
6.8µF
+
Vin
Cc
R
3 ₊ 7 ^0.1µF
VCC
R
2
CLC450 ⁶
2_-
4 _Rf
V_o
Rg
V_o
=
V_in

¹⁺
R_f
R_g


+
2.5
C
low
frequency
cutoff
=
1
2πR_inC_c
,
where:
R_in
=
R
2
R >> R_source
Figure 3: AC Coupled Non-Inverting Configuration
VCC
6.8µF
+
VCC
R
2
3
7
+
0.1µF
Vin ^Cc
Rg
CLC450 ⁶
V_o
2_-
4 _Rf
R
V_o
=
V_in

 ^−
R_f
R_g


+
2.5
low frequency cutoff =
1
2πR_gC_c
Figure 4: AC Coupled Inverting Configuration
Dual Supply Operation
The CLC450 operates on dual supplies as well as single
supplies. The non-inverting and inverting configurations
are shown in Figures 5 and 6.
VCC
6.8µF
+
Vin
3
7
+
0.1µF
Rt
CLC450 ⁶
2_-
Vo
4 _Rf
Rg
0.1µF
6.8µF
VEE
Figure 5: Dual Supply Non-Inverting Configuration
VCC
6.8µF
+
Rb
Vin
Rg
Rt
3
7
+
0.1µF
CLC450 ⁶
2_-
4 _Rf
0.1µF
Vo
Note: Rb provides DC bias
for the non-inverting input.
Select R_t to yield desired
Rin = Rt || Rg.
6.8µF
VEE
Figure 6: Dual Supply Inverting Configuration
Feedback Resistor Selection
The feedback resistor, R_f, affects the loop gain and
frequency response of a current feedback amplifier.
Optimum performance of the CLC450, at a gain of +2V/V,
is achieved with R_f equal to 1kΩ. The frequency response
plots in the Typical Performance sections
illustrate the recommended R_f for several gains. These
recommended values of R_f provide the maximum band-
width with minimal peaking. Within limits, R_f can be
adjusted to optimize the frequency response.
s Decrease R_f to peak frequency response and
extend bandwidth
s Increase R_f to roll off frequency response and
compress bandwidth
As a rule of thumb, if the recommended R_f is doubled,
then the bandwidth will be cut in half.
Unity Gain Operation
The recommended R_f for unity gain (+1V/V) operation
is 1.5kΩ. R_g is left open. Parasitic capacitance at the
inverting node may require a slight increase in R_f to
maintain a flat frequency response.
Bandwidth vs. Output Amplitude
The bandwidth of the CLC450 is at a maximum for
output voltages near 1V_pp. The bandwidth decreases
for smaller and larger output amplitudes. Refer to the
Frequency Response vs. V_o plots.
Load Termination
The CLC450 can source and sink near equal amounts of
current. For optimum performance, the load should be
tied to V_cm.
Driving Cables and Capacitive Loads
When driving cables, double termination is used to
prevent reflections. For capacitive load applications, a
small series resistor at the output of the CLC450 will
improve stability and settling performance. The
Frequency Response vs. C_L and Recommended R_s
vs. C_L plots, in the typical performance section, give the
recommended series resistance value for optimum
flatness at various capacitive loads.
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