Demonstration board and accessories

AN4146

10/30

DocID023502 Rev 2

1.5.1

Power supply

The STA321MP processor needs 3.3 V as a supply voltage while the operative voltage

range of the microphones is 1.64 V - 3.6 V where the typical value is 1.8 V. For this reason

there are two voltage regulators onboard. One regulator is used to generate the 3.3 V from

an external 5 V supply (J20) while the other one generates the 1.8 V from the 3.3 V. The

3.3 V can also be provided from the APWLink connector on pin 11 and enabled on the board

by closing JP1. In spite of the fact that the STEVAL-CCA035V1 board is always connected

demonstration board also hosts the 3.3 V regulator (scaled by an external 5 V supply) to

allow better noise immunity. The following diagram depicts the supply lines scheme: S2

(R78-R79) selects the 3.3 V source while S3 (R80-R81) selects either 1.8 V or 3.3 V as the

microphone supply voltage. These selectors are indicated on the board with the serigraphy

3V3 SEL and MIC_VCC, respectively.

Figure 8. Power supply - block diagram subsection

Once the 3.3 V voltage supply has been chosen, the devices that are fed with this voltage

are the STA321MP, the flip-flop, the level shifter and the opamp. Regarding the

microphones section, the selector S3 offers the possibility to choose their supply level.

Regulator

1.8V

Regulator

3.3V

Gnd +5V

JP1

S3

S2

+3.3V

APWlink

connector