AN2240
Application note
Using the demonstration board for the TS472
low noise microphone preamplifier with 2 V bias
Introduction
This application note describes the STEVAL-CCA023V1 demonstration board, specifically
designed to evaluate the TS472 microphone preamplifier.
The document provides information on:
■ the layout of the demonstration board,
■ the board’s components.
About the TS472
The TS472 is an advanced microphone preamplifier solution, especially intended for mobile
multimedia applications, with the following key features.
■ Low noise: 10 nV/√Hz typ. equivalent input noise at F = 1 kHz
■ Fully-differential input/output
■ 2.2 to 5.5 V single supply operation
■ Low power consumption at 20 dB: 1.8 mA
■ Fast start-up time at 0 dB: 5 ms typ.
■ Low distortion: 0.1% typ.
■ 40 kHz bandwidth at -3 dB and adjustable gain
■ Active low standby mode function (1 μA max)
■ Low noise 2.0 V microphone bias output
■ Available in flip-chip lead-free package and QFN24 4 x 4 mm
■ ESD protection (2 kV)
Refer to the TS472 datasheet for complete device information.
August 2009 Doc ID 11677 Rev 4 1/9
www.st.com
Description of the demonstration board AN2240
1 Description of the demonstration board
The STEVAL-CCA023V1 is a demonstration board designed for the TS472 low noise
microphone preamplifier with 2.0 V bias and active-low standby mode.
This demonstration board helps you to customize the conditions in which you conduct
evaluation testing. Specifically, you can:
● set the adjustable gain of the TS472 device,
● use the TS472 built-in 2.0 V bias voltage to bias an electret microphone,
● or, externally bias the electret microphone.
1.1 Setting the adjustable gain
The gain of the TS472 is set by using the P5 connectors.
The connector has 7 jumper positions. By modifying the jumper positions, you can select
any of the following gain values:
● -1.5 dB (minimum possible gain)
● 0dB
● 10 dB
● 20 dB
● 30 dB
● 40 dB
● 41 dB (maximum possible gain)
Refer to Table 1: Demonstration board connector description to see how to place the jumper
to obtain the desired gain value.
1.2 Output bias options
On the board, the R6, R7, R11 component locations are left empty to allow you to evaluate
the TS472 in a typical application with an electret microphone biased by the TS472’s built-in
2.0 V low noise bias output. To use the TS472’s built-in biasing, the P6 connector must be
closed and P7 must be left floating (refer to Table 1: Demonstration board connector
description).
Alternatively, you can use the R10 empty component locations to externally bias the electret
microphone. To do this:
1. connect the external bias voltage using the P7 connector.
2. leave the P6 connector open.
3. assemble the missing components.
2/9 Doc ID 11677 Rev 4
AN2240 Demonstration board connectors
2 Demonstration board connectors
Caution: When you apply the power supply through P3, DO NOT invert the polarity. Doing so will
destroy the amplifier at U1.
Table 1. Demonstration board connector description
Connector Description
P1 Input signal connector (GND, positive and negative input signal).
P2 Output signal connector (GND, positive and negative output signal).
P3 Power connector (V
Standby control connector (V
P4
Standby puts the TS472 in operating mode. A short-circuit between GND and Standby
and GND). Power supply voltage from 2.2 to 5.5 V.
CC
, Standby, GND). A short-circuit between VCC and
CC
puts the TS472 in standby mode.
Selection connector for gain select pin. There are several
possibilities for the value of the TS472 gain. The value of the gain is
written directly on the PCB. For instance, to set the TS472 with a
gain of 20 dB, the jumper must be placed as shown in the diagram.
P5
41dB/max
40dB
30dB
20dB
10dB
0dB
-1.5dB/min
P6 Internal microphone 2.0 V bias voltage connector. P7 must be floating.
P7 External microphone bias voltage connector (Vx and GND). P6 must be open.
Doc ID 11677 Rev 4 3/9
Schematic diagram AN2240
3 Schematic diagram
Figure 1. Demonstration board schematic diagram
68RR5
123
4
P2
P9
N.A.
R9
100nF
C9
POS. OUTPUT
100K
OUTPUT
P8
N.A.
NEG. OUTPUT
100K
R8
C8
100nF
17
16
1KR427KR2470K
R1
BIAS
1 2
3 4
5 6
7 8
9 10
11 12
P5
9
13 14
GAIN SELE CT
1uF
C3
2
Legend:
N.A. ... Not Assembled
100pFC1N.A.
VCC
1uF
C7
100nF
C6
1
2
P3
Vcc
1uF
1
2
P6 Vbias
1
2
P7
C10
BIAS
R10
N.A.
Vx
J1
100pFC2N.A.
2kR6N.A.
MK1
N.A.
OUT+
OUT-
GAIN
SELECT
15
C-
14
C+
20
Vcc
IN-
IN+
U1
C4
N.A.
5
8
100nF
C5
POS. INPUT
NEG. INPUT
123
4
P1
INPUT
BYPASS
21
G
Bias
BIAS
10
BIAS
100nF
2kR7N.A.
STBY
22
4
GND
2.0V
TS472IQT
R11
N.A.
1uF
C11
N.A.
VCC
123
P4
StandBy
4/9 Doc ID 11677 Rev 4
AN2240 Schematic diagram
Table 2. Component list for the TS472 demonstration board
Board marking Quantity Description
C1, C2 0 Not assembled, 0805
C3, C7, C10 3 Capacitor 1 μF/10 V, 0805
C4, C5, C6, C8, C9 5 Capacitor 100 nF/50 V, 0805
C11 0 Not assembled, 0805
R1 1 Resistor 470 k/100 mW, 1%, 0805
R2 1 Resistor 27 k/100 mW, 1%, 0805
R4 1 Resistor 1 k/100 mW, 1%, 0805
R5 1 Resistor 68 R/100 mW, 1%, 0805
R6, R7, R10, R11 0 Not assembled, 0805
R8, R9 2 Resistor 100 k/100 mW, 1%, 0805
P1, P2 2 Vertical pin header 1x4, 2.54 mm pitch
P3, P6, P7 3 Vertical pin header 1x2, 2.54 mm pitch
P4 1 Vertical pin header 1x3, 2.54 mm pitch
P5 1 Vertical pin header 2x7, 2.54 mm pitch
U1 1 TS472IQT
Doc ID 11677 Rev 4 5/9
Demonstration board layout AN2240
4 Demonstration board layout
The following schematics show the different layers and top view of the demonstration board.
Figure 2. PCB top layer Figure 3. PCB bottom layer
Figure 4. Top view of components layout
6/9 Doc ID 11677 Rev 4
AN2240 Conclusion
5 Conclusion
To order the board online, go to http://www.st.com/stonline/domains/buy/buy_dev.htm, and
use the order code STEVAL-CCA023V1.
Doc ID 11677 Rev 4 7/9
Revision history AN2240
6 Revision history
Table 3. Document revision history
Date Revision Changes
13-Jul-2006 1 Initial release.
4-Aug-2006 2 Editorial updates. No technical changes.
6-Mar-2007 3 Added QFN package information.
26-Aug-2009 4 Changed PCB layouts in Chapter 4.
8/9 Doc ID 11677 Rev 4
AN2240
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Doc ID 11677 Rev 4 9/9
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