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ADS131M08: Ground separation and resistor between P, N

David Park
Expert 6800 points
Part Number: ADS131M08


Hi,

Could you answer about below questions?

1. What method is recommended separation of AGND, DGND?

- Customer is evaluating EVM but there is much noise so considering separation of AGND, DGND

- Can net-tie or 0 Ohm resistor be adopted for it?

2. Could you explain purpose of R1 and R2 1K resistor in EVM?

Thanks.

  • 0
    TI__Guru* 98215 points

    David,

    I'll answer the questions in the order they were asked.

    1. Generally, we've recommended a single ground plane for the device, with connections to both analog and digital grounds. However, the layout should give some thought to how the analog and digital currents will return to ground. In the EVM and in the datasheet, the layout is shown with a single ground. Is your customer having problems with the EVM and noise? The noise performance of the EVM should be similar to Table 1 and 2 in the datasheet.

    If they want to separate analog and digital grounds, It can be done, but I suspect they may require more thought into the layout and how the analog and digital currents return through the board. The planes are separated but connected back to each other near or under the device to limit the problems of ground loop voltages. Again, in our experience, the single ground plane has often worked well for our precision ADCs.

    2. A common application of the ADS131M08 is for energy metering and the resistors for R1 and R2 are used to help with that application. For measuring large voltages, R1/R2 can be used as the sense part of a large voltage divider. This would require a large resistor external to the EVM. For measuring large currents, R1/R2 can be used as the burden resistance for a current transformer. If they are not needed, they can be removed by unsoldering them off the board.

    Joseph Wu