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 V
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.
+ on the board.
CC
June 2009 Doc ID 15840 Rev 1 1/13
www.st.com
Board description AN2995

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

Z14
Z4
VCC+
C1
C2
Vin2
Z8 Z3
Vin1
Z1
Z9
Z2
Z5
Vcc+
VCC-
Z6
SHDN
OP AMP
C3 C4
Z13
Vout
Z7 Z12
AM04501
2/13 Doc ID 15840 Rev 1
AN2995 Board layout

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

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.

3.1 Low-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

Z9
Vin1
Z2Z1
Z5

3.2 High-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.
Z4
Vout
Z6
AM04502
4/13 Doc ID 15840 Rev 1
AN2995 Possible configurations

Figure 4. High-pass Sallen-Key configuration

Z4
Z9
Vin1
Z1 Z2
Vout
Z5
Z6
AM04503

3.3 Differential amplifier configuration

The differential amplifier configuration allows the subtraction of two voltages.
The transfer function is: Vout = Vin1 ((Z8+Z4)/Z8 * Z5/(Z1+Z5)) - Z4/Z8*Vin2.
Choosing Z8 = Z1 and Z4 = Z5 gives:
Vout = (Vin1-Vin2)*Z4/Z8
Z6, Z7, Z9, Z12 and Z14 must be "not connected". Z2, Z3 and Z13 must be shorted.

Figure 5. Differential amplifier configuration

Z4
Vin2
Vin1
Z8
Z1
Z5

3.4 In-loop compensation configuration

The goal of this compensation technique is to stabilize an amplifier configuration with a capacitive load. This compensation is called in-loop because the additional components (Z13 and Z4) used to improve the stability are inserted in the feedback loop.
Z5, Z6 and Z8 must be "not connected". Z1, Z2 and Z3 must be shorted.
Vout
AM04504
(a)
a. More information on compensation methods can be found in application note AN2653: Operational amplifier stability
compensation methods for capacitive loading applied to TS507 (see Table 2: Document references).
Doc ID 15840 Rev 1 5/13
Possible configurations AN2995

Figure 6. Compensation: in-loop configuration

Z14
Z4
Z9
Z13
Vin1

3.5 Out-of-loop compensation configuration

A simple compensation method, using only one extra component, consists in adding a resistor (Z13) in series between the output of the amplifier and its load. It is often referred to as the out-of-loop compensation method because the additional component is added outside of the feedback loop.
Z3, Z5, Z6, Z8, Z9 and Z14 must be "not connected". Z1, Z2 and Z4 must be shorted.

Figure 7. Compensation: out-of-loop configuration

Z13
Vin1
Z7
(b)
Vout
Z12
AM04505
Vout
Z12
Z7
AM04506

3.6 AC-coupled circuit configuration

This typical configuration allows you to amplify the AC part only of the input signal. Z2, Z6, Z7, Z9, Z12 and Z14 must be "not connected". No component is shorted.
b. More information on compensation methods can be found in application note AN2653: Operational amplifier stability
compensation methods for capacitive loading applied to TS507 (see Table 2: Document references).
6/13 Doc ID 15840 Rev 1
AN2995 Possible configurations

Figure 8. AC-coupled circuit configuration

Z4
Vin2
Z8
Z3
Vout
Z5
AM04507
Doc ID 15840 Rev 1 7/13
Board schematics and associated products AN2995

Appendix A Board schematics and associated products

A.1 Board schematic

Figure 9. Demonstration board for single operational amplifier in SOT23 and SC70 packages

Z14
NA
Z4
NA
Vccp
62
5
4
SOT23_b
3
1
Vccn
Out
GOut
Vccp
62
5
3
SOT23_t
1
4
Vccn
Z13
NA
2 1
Z7
NA
Z
VGOut
VOut
2 mm Vout
Vout_SMB
NA
Vccp
62
5
3
SC70
1
4
Vccn
Z6
NA
Vin- 2 mm
Vin-_SMB
Vin+ 2 mm
Vin+_SMB
Vccp 2 mm
Vccn 2 mm
Vccp
Vccn
C1
10 nF
C3
10 nF
VIn-
VIn+
GVIn-
GVIn+
C2
4.7 uF
C4
4.7 uF
Z8
NA
Z1
NA
Z3
NA
Z9
NA
Z2
NA
In-
GIn-
5 Z
NA
In+
GIn+
GND 2 mm
AM04526
8/13 Doc ID 15840 Rev 1
AN2995 Board schematics and associated products

A.2 Associated products in SOT23 or SC70 packages

Table 1. List of operational amplifiers in SOT23 or SC70 packages

Product SOT23-5
TSV611
TSV6191
TSV620
TSV621 TSV6290 TSV6291
TSV630
TSV631 TSV6390 TSV6391
TSV911
TSV991
TS507 LMV321 TSV321
TS1851 TS1871
TS321
TS461
TS931
TS941
TS951
TS971
SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b SOT23_b
(1)
/6
SOT23_t SOT23_t
SOT23_6
SOT23_t
SOT23_6
SOT23_t SOT23_6 SOT23_b SOT23_6 SOT23_b
SC70-5/6 Description
SC70-5 SC70-5 SC70-6 SC70-5 SC70-6 SC70-5 SC70-6 SC70-5 SC70-6 SC70-5
11 µA, 120 kHz, RR I/O CMOS op-amp 11 µA, 450 kHz, RR I/O CMOS op-amp 29 µA, 420 kHz, RR I/O op-amp with SHDN 29 µA, 420 kHz, RR I/O CMOS op-amp 29 µA, 1.3 MHz, RR I/O op-amp with SHDN 29 µA, 1.3 MHz, RR I/O CMOS op-amp 60 µA, 880 kHz, RR I/O op-amp with SHDN 60 µA, 880 kHz, RR I/O CMOS op-amp 60 µA, 2.5 MHz, RR I/O op-amp with SHDN 60 µA, 2.5 MHz, RR I/O CMOS op-amp RR I/O 8 MHz op-amp RR I/O 20 MHz op-amp High precision, RR I/O op-amp Low-cost, low-power RR I/O op-amp General-purpose RR I/O op-amp
1.8 V, RR I/O low-power op-amp
1.8 V, RR I/O low-power op-amp Low-power, high-voltage op-amp Output RR low-noise op-amp Output RR micropower op-amp Output RR micropower op-amp RR I/O low-power op-amp Output RR very low-noise op-amp
(c)
1. The SOT23-5 comes with two possible pin configurations as shown in Figure 10 on page 10.
c. Note that operational amplifiers in SOT23-6 or SC70-6 packages (single with standby) can be evaluated but the standby
pin is by default connected to V
and cannot be changed.
CC+
Doc ID 15840 Rev 1 9/13
Board schematics and associated products AN2995

Figure 10. Package pinouts

V
V
Out
CC -
In +
In+
CC-
In -
1
2
3
SOT23-5
SOT23_b
1
2
+
-
3
SOT23-6 - SC70-6
V
5
CC+
V
CC -
4
In-
In+
In -
1
2
+
-
3
V
5
CC+
4
Out
SOT23-5 - SC70-5
SOT23_t
V
6
CC+
5
SHDN
4
Out
AM04527
10/13 Doc ID 15840 Rev 1
AN2995 Ordering information

Ordering information

To order the board online, go to
http://www.st.com/stonline/products/families/evaluation_boards/steval-cca022v1.htm

References

Table 2. Document references

Document
AN2653: Operational amplifier stability compensation methods for capacitive loading applied to TS507 (http://www.st.com/stonline/products/literature/anp/14130.pdf)
Doc ID 15840 Rev 1 11/13
Revision history AN2995

Revision history

Table 3. Document revision history

Date Revision Changes
23-Jun-2009 1 Initial release.
12/13 Doc ID 15840 Rev 1
AN2995
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Doc ID 15840 Rev 1 13/13
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