ST AN2240 APPLICATION NOTE

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