kh232 Fairchild Semiconductor, kh232 Datasheet - Page 4

• Manufacturer Part Number: kh232
• Description: Low Distortion Wideband Op Amp
• Manufacturer: Fairchild Semiconductor

DATA SHEET
Operation
The KH232 is based on the current feedback op amp
topology, a design that uses current feedback instead of
the usual voltage feedback.
The use of the KH232 is basically the same as that of the
conventional op amp (see Figures 1 and 2). Since the
device is designed specifically for low gain applications,
the best performance is obtained when the circuit is used
at gains between ±1 and ±5. Additionally, performance is
optimum when a 250Ω feedback resistor is used.
4
+15V
-15V
49.9Ω
Figure 1: Recommended non-inverting gain circuit
V
V
in
in
Figure 2: Recommended inverting gain circuit
+15V
-15V
R
3.9
R
i
i
3.9
100Ω
R
3.9
g
0.1
R
3.9
g
0.1
5
6
0.1
KH232
+
-
6
5
1
9
33Ω
33Ω
0.1
+
KH232
-
3,7
9
12
1
33Ω
33Ω
3,7
10
12
11
.01
.01
10
11
250Ω
.01
.01
Capactance in µF
250Ω
R
For Z
R
A
f
g
v
Capactance in µF
= 250Ω
|| R
= −
R
A
R
100Ω
in
f
i
L
v
= 50Ω, select
= 250Ω
= 50Ω



V
= 1+
R
R
R
100Ω
o
g
f
L
V



o
R
R
f
g
Layout Considerations
To assure optimum performance the user should follow
good layout practices which minimize the unwanted
coupling of signals between nodes. During initial bread-
boarding of the circuit use direct point to point wiring,
keeping the lead lengths to less than 0.25”. The use of
solid, unbroken ground plane is helpful. Avoid wire-wrap
type pc boards and methods. Sockets with small, short
pin receptacles may be used with minimal performance
degradation although their use is not recommended.
During pc board layout keep all traces short and direct
The resistive body of R
to pin 5 to minimize capacitance at that point. For the
same reason, remove ground plane from the vicinity of
pins 5 and 6. In other areas, use as much ground plane
as possible on one side of the board. It is especially
important to provide a ground return path for current from
the load resistor to the power supply bypass capacitors.
Ceramic capacitors of 0.01 to 0.1µf (with short leads)
should be less than 0.15 inches from pins 1 and 9.
Larger tantalum capacitors should be placed within one
inch of these pins. V
can be made directly from pins 9 and 1, but better supply
rejection and settling time are obtained if they are
separately bypassed as in figures 1 and 2. To prevent
signal distortion caused by reflections from impedance
mismatches, use terminated microstrip or coaxial cable
when the signal must traverse more than a few inches.
Since the pc board forms such an important part of the
circuit, much time can be saved if prototype boards of any
high frequency sections are built and tested early in the
design phase. Evaluation boards designed for either
inverting or non-inverting gains are available.
Offset Voltage Adjustment
If trimming of the input offset voltage (V
desired, a resistor value of 10kΩ to 1MΩ placed between
pins 8 and 9 will cause V
8mV to 0.2mV respectively. Similarly, a resistor placed
between pins 1 and 2 will cause V
positive.
Thermal Considerations
At high ambient temperatures or large internal power
dissipations, heat sinking is required to maintain
acceptable junction temperatures. Use the thermal
model on the previous page to determine junction
temperatures. Many styles of heat sinks are available for
TO-8 packages; the Thermalloy 2240 and 2268 are good
examples. Some heat sinks are the radial fin type which
cover the pc board and may interfere with external
components. An excellent solution to this problem is to
use surface mounted resistors and capacitors. They
have a very low profile and actually improve high
frequency performance. For use of these heat sinks with
conventional components, a 0.1” high spacer can be inserted
under the TO-8 package to allow sufficient clearance.
CC
g
should be as close as possible
os
connections to pins 10 and 12
to become more negative by
os
, to become more
REV. 1A February 2001
os
= V
ni
-V
KH232
in
) is