august 2009 doc id 11677 rev 4 1/9 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-c ca023v1 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 a 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. www.st.com
description of the demonstration board AN2240 2/9 doc id 11677 rev 4 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 electr et 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.
AN2240 demonstration board connectors doc id 11677 rev 4 3/9 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 cc and gnd). power supply voltage from 2.2 to 5.5 v. p4 standby control connector (v cc , standby, gnd). a short-circuit between v cc and standby puts the ts472 in operating mode. a short-circuit between gnd and standby puts the ts472 in standby mode. p5 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. 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. 0db 10db 20db -1.5db/min 40db 30db 41db/max
schematic diagram AN2240 4/9 doc id 11677 rev 4 3 schematic diagram figure 1. demonstration board schematic diagram vcc 1uf c3 68r r5 1k r4 27k r2 470k r1 vcc 1uf c7 100nf c6 100pf c1 n.a. 100pf c2 n.a. 100nf c4 100nf c5 2k r6 n.a. 2k r7 n.a. 1 2 3 4 p1 input 1 2 3 4 p2 output pos. input neg. input neg. output pos. output 100nf c8 100nf c9 100k r8 100k r9 1uf c10 1 2 p3 vcc 1 2 3 p4 standby 1 2 p6 vbias 1 2 p7 vx r10 n.a. 1uf c11 n.a. r11 n.a. bias bias bias bias stby in- in+ g c+ c- out+ out- gain bypass bias gnd vcc select 20 14 15 17 16 9 2 21 4 10 5 8 2.0v 22 u1 ts472iqt 1 2 3 4 5 6 7 8 9 10 11 12 13 14 p5 gain select mk1 n.a. p9 n.a. p8 n.a. j1 n.a. n.a. ... not assembled legend:
AN2240 schematic diagram doc id 11677 rev 4 5/9 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 f/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
demonstration board layout AN2240 6/9 doc id 11677 rev 4 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
AN2240 conclusion doc id 11677 rev 4 7/9 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.
revision history AN2240 8/9 doc id 11677 rev 4 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 .
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