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MCP4922 DAC and MCP3204 ADC ground pins. Where to connect them ?

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lukasz.kostka:
HI.

I'd like to create a daughter board with DAC, ADC and reference voltage. I have a problem where to connect ground pins. Datasheet for MCP3204 states on page 24 that both AGND and DGND should be connected to analog ground. I am confused, why separate pins on IC since they need to be connected to same ground plane ? DAC has only one GND pin. Where should I connect it ? GNDA or GNDD ?

exe:
That's because an external trace has lower resistance than the internal connection. Designators such as AGND and DGND do not tell where the pins should be connected. They only tell where they are internally connected.

More details here: https://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html

Relevant excerpt from there:


--- Quote ---Many ADCs and DACs have separate analog ground (AGND) and digital ground (DGND) pins. On the device data sheets, users are often advised to connect these pins together at the package. This seems to conflict with the advice to connect analog and digital ground at the power supplies, and, in systems with more than one converter, with the advice to join the analog and digital ground at a single point.

There is, in fact, no conflict. The labels, “analog ground” and “digital ground,” on these pins refer to the internal parts of the converter to which the pins are connected and not to the system grounds to which they must go. For an ADC, these two pins should generally be joined together and to the analog ground of the system. It is not possible to join the two pins within the IC package because the analog part of the converter cannot tolerate the voltage drop resulting from the digital current flowing in the bond wire to the chip. But they can be tied together externally.

--- End quote ---

lukasz.kostka:
So DAC, ADC and reference voltage GND pins should be connected to AGND. Of course I need to place DGND under the SPI lines. Am I right ?

lukasz.kostka:
And I can not connect at some cpoint on my daughter board two ground planses, because I will create a groud loop. Right ?

T3sl4co1l:
If you don't have extremely specific requirements, and you don't have the skills to resolve a split-plane design -- better to simply pour ground over everything, and keep the digital to one side and the analog to the other side. :-+

Tim

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