MCP3462 datasheet(80/108 Pages) MICROCHIP

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MCP3461/2/4

DS20006180D-page 80

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7.4

SPI Interface Digital Crosstalk

The MCP3461/2/4 incorporates a high-speed 20 MHz

SPI digital interface. This interface can induce

crosstalk, especially with the outer channels closer to

the SPI digital pins (CH7, for example), if it is running at

full speed without any precautions. The crosstalk is

caused by the switching noise created by the digital

SPI signals. This crosstalk would negatively impact the

SNR in this case. The noise is attenuated if proper

separation between the analog and digital power

supplies is put in place (see Section 7.3 “Power Sup-

ply Design and Bypassing”).

The switching noise is also a linear function of the

DVDD supply voltage. In order to reduce further the

influence of the switching noise caused by SPI

transmissions, the DVDD digital power supply voltage

should be kept as low as possible.

In order to further remove the influence of the SPI

communication on measurement accuracy, it is recom-

mended to add series resistors on the SPI lines to

reduce the current spikes caused by the digital switch-

ing noise (see Figure 7-1, where these resistors have

been implemented). The resistors also help to keep the

level of electromagnetic emissions low.

The

measurement

graphs

provided

this

MCP3461/2/4 data sheet have been performed with

100

 series resistors connected on each SPI I/O pin.

Measurement accuracy disturbances have not been

observed, even at 20 MHz interfacing.

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