Hardware description

AN4041

6/14

Doc ID 022706 Rev 2

2

Hardware description

The board is a sound card automatically recognized by the PC as an audio device. The

connection is done through the USB cable which also supplies the board and then streams

the audio collected from the microphones to the PC.

Figure 3.

Microphone USB demonstration board (block diagram)

Supply section

The supply section of the board is made up of two voltage regulators that step down the 5 V

of the USB connection to 3.3 V and 2.5 V. The solder jumper J4 gives the user the possibility

to choose the desired supply voltage.The digital microphone voltage ranges are given in the

following table.

We recommend using 2.5 V to avoid supplying the microphone with a voltage that is too

high. For instance, the MP34DT01 cannot support a supply voltage of 3.3 V.

Microphone section

Regarding the microphone section, the MEMS outputs are a PDM signal, which is a high-

frequency stream (1 to 3.25 MHz) of 1-bit digital samples. According to the application hints

channel configuration or stereo configuration by setting the LR pin. This pin sets the validity

Table 1.

Microphone supply voltage range

Part number

Min.

Typ.

Max.

Unit

MP45DT02

1.64

1.8

3.6

V

MP34DB01

1.64

1.8

3.6

V

MP34DT01

1.64

1.8

3.6

V

STM32F107RC

12.288 MHz

SEL

L/R

Clk

Vdd

Out

gnd

APWlink

connector

SPI

USB I/F

8 MHz

L/R

Clk

Vdd

Out

gnd

SEL

Regulator

2.5V

Regulator

3.3V

SEL

5V

Mic_Vdd

µC_Vdd

USB

Connector

2.5V

3.3V

OSC

Mic_Vdd

J4

J1

J5

SPI_CK

APWlink+

Timer

MIC_CK

MIC_CK

MIC_DATA12

Mic_Vdd

D1

D2

D3

D4

D5

Mic_Vdd

Mic_Vdd

µC_Vdd