AN2240 Application note
Using the evaluation board for the TS472 low noise microphone preamplifier with 2V bias
Introduction
This application note describes the DEMO TS472 evaluation board, specifically designed to evaluate the TS472 microphone preamplifier. In this document, you will find information about:
Evaluation board layout Evaluation board components
About the TS472
The TS472 is an advanced microphone preamplifier solution, especially intended for mobile multimedia applications. Its key features are:
Low noise: 10nV/ z typ. equivalent input noise @ F=1kHz H Fully differential input/output 2.2V to 5.5V single supply operation Low power consumption @20dB: 1.8mA Fast start up time @ 0dB: 5ms typ. Low distortion: 0.1% typ. 40kHz bandwidth @ -3dB and adjustable gain Active low standby mode function (1A max) Low noise 2.0V microphone bias output Available in flip-chip lead-free package and QFN24 4x4mm ESD protection (2kV)
For complete information about the TS472, please refer to the datasheet.
March 2007
Rev 3
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Description of the evaluation board
AN2240
Description of the evaluation board
The DEMO TS472 is an evaluation board designed for the TS472 low noise microphone preamplifier with 2.0V bias and active-low standby mode. This evaluation board helps you to customize the conditions in which you conduct evaluation testing. Specifically, using the board, you can:
set the adjustable gain of the TS472 device, use the TS472 built-in 2.0V bias voltage to bias an electret microphone, or, externally bias the electret microphone.
Setting the adjustable gain
The gain of the TS472 is set by using the P8 and P9 connectors (refer to Table 1: Evaluation board connector description). These connectors have 4 (P8) and 5 (P9) jumper positions. By modifying the jumper positions, you can select any of the following gain values:
-1.5dB (the minimum possible gain) 0dB 10dB 20dB 30dB 40dB 41dB (the maximum possible gain)
Refer to Table 1: Evaluation board connector description to see how to place the jumpers to obtain the gain value you want.
Output bias options
On the board, the R6 and R7 component locations are left empty to allow you to evaluate the TS472 in a typical application with an electret microphone biased by the TS472 built-in 2.0V low noise bias output. To use the TS472's built-in biasing, the P11 connector must be closed and P10 must be left floating (refer to Table 1: Evaluation board connector description). Alternatively, you can use the R10, R11 and C11 empty component locations to externally bias the electret microphone. To do this: 1. 2. Connect the external bias voltage using the connector P10. Leave connector P11 open.
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AN2240
Evaluation board connectors
Evaluation board connectors
Caution: When you apply the power supply through Cn9, do not invert the polarity because it would destroy the amplifier at U1. Table 1.
Connector P1 P2 P3, P4 P5 P6
Evaluation board connector description
Description Input signal connector (GND, positive and negative input signal). Output signal connector (GND, positive and negative output signal). Connectors for TS472 adapter Power connector (VCC and GND). Power supply voltage from 2.2V to 5.5V. Standby control connector (VCC, Standby, GND). A short-circuit between VCC and Standby puts the TS472 in operating mode. A short-circuit between GND and Standby puts TS472 in standby mode. Selection connector for gain select pin. When a jumper is put on:
Rgs Max
Jumper
Rgs, the gain of the TS472 is determined by connector P9 (see below) Max, Min, Bias,
P8
Min Bias
the gain of the TS472 is maximum (typ. 41dB) the gain of the TS472 is minimum (typ. -1.5dB) the gain of the TS472 is 20dB typ. the gain of the TS472 is 0dB typ. the gain of the TS472 is 20dB typ. the gain of the TS472 is 30dB typ. the gain of the TS472 is 40dB typ.
68R 1k
Selection connector for Rgs resistor. When a jumper is put on:
Jumper
68R, 1k, 4k7, 27k,
P9
4k7 27k 470k
the gain of the TS472 is 10dB typ.
470k,
P10 P11
External microphone bias voltage connector (Vx and GND); P11 must be open. Internal microphone 2.0V bias voltage connector; P10 must be floating.
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2
1 2 2 1 1 1 1 1 100pF 2 C7 1uF 1 R6 100pF R8 100k 2 14 3 1 TS472_Adapter 100nF 1 C2 2 1 C8 2 R9 100k POS. OUTPUT NEG. OUTPUT 100nF 2 1 2 R10 2 Bias 2 C6 100nF Vcc
1
1
2
2
1
C1
P1 100nF 6
IN+ OUT+ OUT12
C2
1
1
2
1
1
2
R11 9 15
GND
STDBY
2
2
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Schematic diagram
Figure 1.
Jumper J4
P10 P11 Vbias 1 2 C1 P2 4 3 2 1 C9 VCC
P5
Schematic diagram
Vx
C10 1uF
OUTPUT
1 13
C4 2
Vcc
4 3 2 1 8
POS. INPUT NEG. INPUT
Jumper J2
IN-
INPUT 100nF
1
C5 2
Evaluation board schematic diagram
Gain
Bias 4
GAIN SELECT
5
P8
Bias Bias Min Max Rgs 8 6 4 2 7 5 3 1
R7
BIAS Bias
BYPASS
10
C3 1uF
Gain Select 1 R1 470k P9 1 R2 27k 1 R3 2 2
C11
P6 Jumper J1 1 2 3 StandBy
VCC
2 4.7k Rgs 1 R4 1k 1 R5 Jumper J3 68 2 2
470k 27k 4k7 1k 68R
1 3 5 7 9
2 4 6 8 10
AN2240
AN2240 Table 2. Component list for the TS472 evaluation board
Quantity 2 3 5 0 4 2 2 3 1 1 1 1 1 1 1 1 0 2 1 Description 100pF/50V, ceramic capacitors, 0805 1F/50V, electrolytic capacitor 100nF/16V, ceramic capacitors, 0805 Not connected Jumper, 2.54mm pitch Ver tical pin header 1x4, 2.54mm pitch Ver tical pin header 1x8, 2.54mm pitch Ver tical pin header 1x2, 2.54mm pitch Ver tical pin header 1x3, 2.54mm pitch Ver tical pin header 2x4, 2.54mm pitch Ver tical pin header 2x5, 2.54mm pitch 68 1/16 1% resistor, 0805 , 1k 1/16 1% resistor, 0805 , 4.7k 1/16 1% resistor, 0805 , 27k 1/16 1% resistor, 0805 , 470k 1/16 1% resistor, 0805 , Not connected 100k 1/16 1% resistor, 0805 ,
Schematic diagram
Board marking C1, C2 C3, C7, C10 C4, C5, C6, C8, C9 C11 J1, J2, J3, J4 P1, P2 P3, P4 P5, P10, P11 P6 P8 P9 R1 R2 R3 R4 R5 R6, R7, R10, R11 R8, R9 TS472 adapter
PCB adapter assembled by TS472 (either flip-chip or QFN24 4x4 package), connected into connectors P3 and P4
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Evaluation board layout
AN2240
Evaluation board layout
The following schematics show the different layers and the top view of the evaluation board. Figure 2. PCB top layer Figure 3. PCB bottom layer
Figure 4.
Top view of components layout
Revision history
Date 13-Jul-2006 4-Aug-2006 6-Mar-2007 Revision 1 2 3 Initial release. Editorial updates. No technical changes. Added QFN package information. Changes
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