OPA623 Datasheet, PDF (12/15 Pages) Burr-Brown (TI) – Wide Bandwidth, Current-Feedback OPERATIONAL AMPLIFIER

CIRCUIT LAYOUT
The high-frequency performance of the operational ampli-
fier OPA623 can be greatly affected by the physical layout
of the printed circuit board. The following tips are offered as
suggestions. Oscillations, ringing, poor bandwidth and set-
tling, and peaking are all typical problems that plague high-
speed components when they are used incorrectly.
• A resistor (100Ω to 250Ω) in series and close to the high-
impedance, noninverting input is necessary to reduce
peaking; this resistor prevents any very high-frequency
oscillations at the op amp input, which can lead to an
excessive increase in quiescent current.
• Bypass power supplies very close to the device pins. Use
tantalum chip capacitors (approximately 2.2µF) with a
parallel 470pF ceramic chip capacitor. Surface-mount
types are recommended because of their low lead induc-
tance. Although the OPA623 operates at a low quiescent
current, high charging and discharging currents flow
during steep transitions.
• PC board traces for power lines should be wide to reduce
impedance and inductance.
• Make short low-inductance traces. The entire physical
circuit should be as small as possible.
• Use a low-impedance ground plane on the component
side to ensure that low-impedance ground is available
throughout the layout, however, do not extend the ground
plane under high-impedance nodes such as the amplifier’s
input terminals, which are sensitive to stray capacitances.
• Sockets are not recommended because they add signifi-
cant inductance and parasitic capacitance.
• Use low-inductance, surface-mounted components. Cir-
cuits using all surface-mount components with the
OPA623AU will offer the best AC performance.
• Plug-in prototype boards and wire-wrap boards will not
function well. A clean layout using RF techniques is
essential—there are no shortcuts.
• Make the feedback trace as short as possible. The invert-
ing input is sensitive to stray capacitances that lead to
peaking in the frequency response. A stray capacitance at
the inverting input increases the gain at high frequencies.
Non Inverting
In+
In–
R_{i 3}
7
OPA623 ⁶
2
R₃
4
50Ω
R₁
R_O
50Ω
R₂
Inverting
R_{i 3}
7
R_O
50Ω
6
OPA623
2
4
R_N1
R₁
R_N2
Out
+5V
7
C1
C3
C5
470pF 10nF
2.2µF
Gnd
C2
C4
C6
470pF 10nF
2.2µF
–5V
4
Out
FIGURE 10. Circuit Schematic for Non-inverting and Inverting Configuration. Refer to Table I for Resistor Values.
COMPONENT
OPA623AP
GAIN
–2
–1
+1
+2
R_i
R₁
R₂
R_N1
R_N2
Typical
Bandwidth (MHz)
V_OUT = 0.2Vp-p
V_OUT = 2.8Vp-p
150Ω
390Ω
—
200Ω
68Ω
200
330
150Ω
390Ω
—
390Ω
56Ω
—
360
200Ω
360Ω
—
—
—
320
340
180Ω
300Ω
300Ω
—
—
290
350
TABLE I. Recommended Component Values.
®
OPA623
+5
100Ω
300Ω
75Ω
—
—
+10
100Ω
130Ω
15Ω
—
—
—
170
260
210
12
–2
150Ω
390Ω
—
200Ω
68Ω
200
330
–1
150Ω
390Ω
—
390Ω
56Ω
—
360
OPA623AU
GAIN
+1
+2
270Ω
470Ω
—
—
—
180Ω
300Ω
300Ω
—
—
320
290
340
350
+5
100Ω
300Ω
76Ω
—
—
+10
100Ω
160Ω
18Ω
—
—
—
170
260
210