TLC072-Q1_15 Datasheet, PDF (15/24 Pages) Texas Instruments – WIDE-BANDWIDTH HIGH-OUTPUT-DRIVE SINGLE-SUPPLY OPERATIONAL AMPLIFIER

TLC072-Q1
www.ti.com ...................................................................................................................................................................................................... SLOS583 – JUNE 2008
If even more attenuation is needed, a multiple pole filter is required. The Sallen-Key filter can be used for this
task (see Figure 42). For best results, the amplifier should have a bandwidth that is 8 to 10 times the filter
frequency bandwidth. Failure to do this can result in phase shift of the amplifier.
C1
V_I
R1
+
R2
_
C2
R_F
R_G
R1 = R2 = R
C1 = C2 = C
Q = Peaking Factor
(Butterworth Q = 0.707)
f–3dB
+
1
2pRC
( ) ^{RG =}
R_F
1
2− _Q
Figure 42. Two-Pole Low-Pass Sallen-Key Filter
Circuit Layout Considerations
To achieve the levels of high performance of the TLC072, follow proper printed-circuit board design techniques.
A general set of guidelines is given in the following.
• Ground planes
A ground plane should be used on the board to provide all components with a low inductive ground
connection. However, in the areas of the amplifier inputs and output, the ground plane can be removed to
minimize the stray capacitance.
• Proper power supply decoupling
Use a 6.8-µF tantalum capacitor in parallel with a 0.1-µF ceramic capacitor on each supply terminal. It may be
possible to share the tantalum among several amplifiers depending on the application, but a 0.1-µF ceramic
capacitor should always be used on the supply terminal of every amplifier. In addition, the 0.1-µF capacitor
should be placed as close as possible to the supply terminal. As this distance increases, the inductance in the
connecting trace makes the capacitor less effective. The designer should strive for distances of less than
0.1 inch between the device power terminals and the ceramic capacitors.
• Sockets
Sockets can be used but are not recommended. The additional lead inductance in the socket pins often leads
to stability problems. Surface-mount packages soldered directly to the printed-circuit board is the best
implementation.
• Short trace runs/compact part placements
Optimum high performance is achieved when stray series inductance has been minimized. To realize this, the
circuit layout should be made as compact as possible, thereby minimizing the length of all trace runs.
Particular attention should be paid to the inverting input of the amplifier. Its length should be kept as short as
possible. This will help to minimize stray capacitance at the input of the amplifier.
• Surface-mount passive components
Using surface-mount passive components is recommended for high performance amplifier circuits for several
reasons. First, because of the extremely low lead inductance of surface-mount components, the problem with
stray series inductance is greatly reduced. Second, the small size of surface-mount components naturally
leads to a more compact layout thereby minimizing both stray inductance and capacitance. If leaded
components are used, it is recommended that the lead lengths be kept as short as possible.
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