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ADS131M06: ADS131M06 + SPI ISOLATOR WITH INTEGRATED POWER (2 forward - 2 backward)

Roosbel Guaya
Prodigy 115 points

Part Number: ADS131M06
Other Parts Discussed in Thread: ISOW7742

Hi:
I am looking at the viability of the ADS131M06 and its family of working with a CS tied low all the time (PULLDOWN Resistor).
I want to use it with a isolator, in particular ISOW7742, where i use it because of the Data-Ready that i have to bring from the isolated side to the MCU side.

So:
MOSI -> adcMOSI

SCK -> adcSCK
MISO <- adcMISO

Data-Ready <- adcDR

So will the SPI interface of the ADS131M06 continue to work correctly even when it is tied to GND the CS?
I have seen that there is a SPI timeout  32768 CLKIN -> which at 8.192MHZ will be 4ms?
I want to have a 4ksps data sampling so that would be a no go if I need to use the SPI timeout...

The other option would be to use a 6 channel digital isolator, but i would prefer to have all integrated in one IC like the ISOW7742.

R.

  • +1
    TI__Guru 50665 points

    Hi Roosbel Guaya,

    ADS131M06 supports 3-wire SPI mode and the /CS can be tied to GND. The ADC communicates in frames of a fixed length. See the SPI Communication Frames section in the datasheet for details regarding SPI data framing on the ADS131M06.  Make sure you send the correct number of SCLKs to the ADC for commands or data collection. The output CRC cannot be disabled and it always appears at the end of the output frame. The host can ignore the CRC data in normal 4-wire SPI mode if the output CRC is not used, but the host should send the last word for CRC in 3-wire SPI mode.

    Your calculation of the timeout is correct, but one cycle of 4ksps is 0.25ms only, I did not see an issue if you wan to use the timeout. You can use your own definition of timeout on your host if you want.

    BR,

    Dale

  • 0 in reply to Dale Li
    Prodigy 115 points

    Hi:
    Many thanks.
    I did the modification on another board that i had one of these adcs with all the pins of the interface, non isolated. The modification was pulling the cs low with a resistor and it did work correctly when i deactivated the CS of the MCU.

    R.