ST AN2995 APPLICATION NOTE
AN2995
Demonstration board user guidelines for single operational amplifiers
Introduction
This demonstration board is designed to help in the characterization of single operational amplifiers in SOT23-5 (two different pinouts) and SC70-5 packages. Operational amplifiers in SOT23-6 and SC70-6 packages can also be characterized, but their respective standby pin cannot be used since it is connected to VCC+ on the board.
This document provides:
■a brief description of the demonstration board.
■a layout of the top and bottom layers.
■some examples of typical configurations that can be tested with the board.
June 2009 |
Doc ID 15840 Rev 1 |
1/13 |
www.st.com
Board description |
AN2995 |
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1 Board description
This board is designed with versatility in mind. In particular, its components allow it to be configured as:
●a low-pass Sallen-Key circuit.
●a high-pass Sallen-Key circuit.
●a differential amplifier.
●an AC-coupled circuit.
●an in-loop compensation circuit.
●an out-of-loop compensation circuit.
●and numerous other possible configurations not described here.
The board is designed for surface-mounted components in SOT23-5 (and SOT23-6) or SC70-5 (SC70-6) packages. It can be used to perform on-board characterization prior to the integration of STMicroelectronics’ products in your designs. Resistor and capacitor footprints are implemented in the 0805 series.
A set of two decoupling capacitors have been implemented on both power supply pins so as to benefit from the maximum performances of ST products. In order to reject a wide range of frequencies, 100 nF and 4.7 µF are good values for these capacitors.
Figure 1. Demonstration board schematics
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Z14 |
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Z4 |
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VCC+ |
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C1 |
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C2 |
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Vin2 |
Z8 |
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Z9 |
Z3 |
Vcc+ |
SHDN |
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Vout |
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OP AMP |
Z13 |
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Vin1 |
Z1 |
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Z2 |
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Z7 |
Z12 |
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Z5 |
VCC- |
C3 |
C4 |
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Z6 |
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AM04501 |
2/13 |
Doc ID 15840 Rev 1 |
AN2995 |
Board layout |
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2 Board layout
The board has the following physical characteristics.
●Board dimensions: 2080 x 1900 mils (52.8 x 48.3 mm).
●2-layer PCB.
For Vout, Vin1 and Vin2, male SMB or 2-mm female connectors can be implemented. You can also implement test points on these three voltages to facilitate visualization of your signals.
Figure 2 shows the top and bottom layers of the board.
Figure 2. Top and bottom layers
Doc ID 15840 Rev 1 |
3/13 |
Possible configurations |
AN2995 |
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3 Possible configurations
This chapter provides instructions on how to set-up the board with several typical configurations.
●Figure 3: low-pass Sallen-Key configuration
●Figure 4: high-pass Sallen-Key configuration
●Figure 5: differential amplifier configuration
●Figure 6: in-loop compensation configuration
●Figure 7: out-of-loop compensation configuration
●Figure 8: AC-coupled configuration
You can also connect several boards together if you need to evaluate more complicated schematics using several operational amplifiers.
3.1Low-pass Sallen-Key configuration
The low-pass Sallen-Key configuration is a second-order filter configuration. Z4 and Z9 are used to set the gain.
Fc = 1/(2*PI*sqrt(Z1*Z2*C5*C6))
Z7, Z8, Z12 and Z14 must be "not connected". Z3 and Z13 must be shorted.
Figure 3. Low-pass Sallen-Key configuration
Z4
Z9
Vout
Vin1
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Z1 |
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Z2 |
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Z5 |
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Z6
AM04502
3.2High-pass Sallen-Key configuration
Like the low-pass Sallen Key configuration, this is also a second-order filter configuration. Z4 and Z9 are used to set the gain.
Fc = 1/(2*PI*sqrt(C1*C2*Z5*Z6))
Z7, Z8, Z12 and Z14 must be "not connected". Z3 and Z13 must be shorted.
4/13 |
Doc ID 15840 Rev 1 |
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