HFA-0005 INTERSIL [Intersil Corporation], HFA-0005 Datasheet - Page 9

• Manufacturer Part Number: HFA-0005
• Description: High Slew Rate Operational Amplifier
• Manufacturer: INTERSIL [Intersil Corporation]

Applications Information
Offset Adjustment
When applications require the offset voltage to be as low as
possible, the figure below shows two possible schemes for
adjusting offset voltage.
For a voltage follower application, use the circuit in Figure 29
without R
10MΩ, so the adjustment resistors will cause only a very
small gain error.
PC Board Layout Guidelines
When designing with the HFA-0005, good high frequency
(RF) techniques should be used when making a PC board. A
massive ground plane should be used to maintain a low
impedance ground. Proper shielding and use of short
interconnection leads are also very important.
To achieve maximum high frequency performance, the use
of low impedance transmission lines with impedance
matching is recommended: 50Ω lines are common in
communications and 75Ω lines in video systems. Impedance
matching is important to minimize reflected energy therefore
minimizing
accomplished by using a series matching resistor (50Ω or
75Ω), matched transmission line (50Ω or 75Ω), and a
matched terminating resistor, as shown in Figure 30. Note
that there will be a 6dB loss from input to output. The
HFA-0005 has an integral 50Ω ±20% resistor connected to
the op amp’s output with the other end of the resistor pinned
out. This 50Ω resistor can be used as the series resistor
instead of an external resistor.
Adjustment Range
50K
50K
+V
-V
2
+5V
-5V
and with R
FIGURE 29. NON-INVERTING GAIN
transmitted
Adjustment Range
100K
V
R
FIGURE 28. INVERTING GAIN
IN
1
≅
100K
±
R
R
V
I
1
I
R
100

shorted. R
2
R
---- -
R
V
R
2
1
IN
I


signal
R
100
2
G a in
≅
R
1
50
+
F
±
should then be 1MΩ to
distortion.
V
+
≅

R
F
R
-----
R 1
1
2
+



---------------
R
I
V
R
+
OUT
This
F
V
R
OUT
2
HFA-0005


is
9
PC board traces can be made to look like a 50Ω or 75Ω
transmission line, called microstrip. Microstrip is a PC board
trace with a ground plane directly beneath, on the opposite
side of the board, as shown in Figure 31.
When manufacturing pc boards the trace width can be calcu-
lated based on a number of variables.
The following equation is reasonably accurate for calculating
the proper trace width for a 50Ω transmission line.
Power supply decoupling is essential for high frequency op
amps. A 0.01µF high quality ceramic capacitor at each
supply pin in parallel with a 1µF tantalum capacitor will
provide excellent decoupling. Chip capacitors produce the
best results due to ease of placement next to the op amp
and they have negligible lead inductance. If leaded capaci-
tors are used, the leads should be kept as short as possible
to minimize lead inductance. The figures that follow illustrate
two different decoupling schemes. Figure 33 improves the
PSRR because the resistor and capacitors create low pass
filters. Note that the supply current will create a voltage drop
across the resistor.
V
IN
GROUND
PLANE
+
R
F
Z
0
SIGNAL
h
TRACE
=
-------------------------
E
R
50Ω
87
FIGURE 30.
FIGURE 31.
FIGURE 32.
+
+
1.41
V+
V-
w
50Ω
0.01µF
0.01µF
1.0µF
1.0µF
In

COAX CABLE
E
----------------- -
0.8 w
R
5.98h
+
t
 Ω

DIELECTRIC
(PC BOARD)
50Ω
V
OUT
t