AN2834 datasheet(30/45 Pages) STMICROELECTRONICS

30 / 45 page

How to get the best ADC accuracy

AN2834

30/45

DocID15067 Rev 2

3.2.12

PCB layout recommendations

Separating the analog and digital layouts

It is recommended to separate the analog and digital circuitry on the PCB (see Figure 29).

This also avoids tracks crossing each other. The tracks carrying digital signals may

introduce high-frequency noise in analog signals because of coupling.

The digital signals produce high-frequency noise because of fast switching.

Coupling of a capacitive nature is formed due to the metal connections (tracks) separated

by the dielectric provided by the PCB base (glass, ceramic or plastic).

It is recommended to use different planes for analog and digital grounds. If there is a lot of

analog circuitry then an analog ground plane is recommended. The analog ground must be

placed below the analog circuitry.

Figure 29. Separating the analog and digital layouts

Separating the analog- and digital-circuit power supplies

It is desirable to have separate analog and digital power supplies in cases where there is a

lot of analog and digital circuits external to the microcontroller (see Figure 30). Depending

on the STM32x package, different analog and digital power supply and ground pins are

available. The VDDA/VREF+ and VDD pins can be powered from separate power supplies.

If you use a switching-type power supply for the digital circuitry, you should use a separate

linear supply for the analog circuit. Also, if you expect a lot of noise on the DC power supply

due to I/O switching etc., it is preferable to use a separate supply for the analog circuit.

Figure 30.

Separating the analog and digital supplies

Digital

circuitry

Analog

circuitry

STM32

Power

supply

Analog

ground

Digital

ground

plane

(Noise generator)

(Affected by noise)

ai15492

VDDA

VREF+

VSSA

STM32

VREF-

VDD

Vout1

Vout2

GND

VSS

SMPS

Linear

regulator

Analog

Circuit

Star

Network

ai15493

AN2834 датащи(PDF) 30 Page - STMicroelectronics

AN2834 датащи(HTML) 30 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45

датащи скачать

ссылки URL