OPA322_16 Datasheet, PDF (16/38 Pages) Texas Instruments – CMOS Operational Amplifier with Shutdown

OPA322, OPA322S
OPA2322, OPA2322S
OPA4322, OPA4322S
SBOS538E – JANUARY 2011 – REVISED JUNE 2012
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The DFN package can easily be mounted using standard PCB assembly techniques. See the application reports,
QFN/SON PCB Attachment (SLUA271) and Quad Flatpack No-Lead Logic Packages (SCBA017), both available
for download at www.ti.com. The exposed leadframe die pad on the bottom of the DFN package should be
connected to the most negative potential (V–). The dimension of the exposed thermal die pad is 2 mm ×
1,2 mm and is centered.
APPLICATION EXAMPLES
ACTIVE FILTER
The OPA322 is well-suited for active filter applications that require a wide bandwidth, fast slew rate, low-noise,
single-supply operational amplifier. Figure 37 shows a 500-kHz, second-order, low-pass filter using the multiple-
feedback (MFB) topology. The components have been selected to provide a maximally-flat Butterworth response.
Beyond the cutoff frequency, roll-off is –40 dB/dec. The Butterworth response is ideal for applications that require
predictable gain characteristics, such as the anti-aliasing filter used in front of an ADC.
One point to observe when considering the MFB filter is that the output is inverted, relative to the input. If this
inversion is not required, or not desired, a noninverting output can be achieved through one of these options:
1. adding an inverting amplifier;
2. adding an additional second-order MFB stage; or
3. using a noninverting filter topology, such as the Sallen-Key (shown in Figure 38).
MFB and Sallen-Key, low-pass and high-pass filter synthesis is quickly accomplished using TI’s FilterPro™
program. This software is available as a free download at www.ti.com.
R₃
549 W
C₂
150 pF
R₁
R₂
549 W 1.24 kW
V_IN
C₁
1 nF
V+
OPA322
V-
V_OUT
Figure 37. Second-Order Butterworth 500-kHz Low-Pass Filter
V_IN = 1 V_RMS
1.8 kW
220 pF
V+
19.5 kW 150 kW
3.3 nF
47 pF ^OPA322
V_OUT
V-
Figure 38. OPA322 Configured as a Three-Pole, 20-kHz, Sallen-Key Filter
16
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