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TMP126: Valid operation range of SPI bus clock

Bin Wei
Prodigy 10 points
Part Number: TMP126

Per the datasheet for tmp126, the maximum supported SPI bus speed is 10 MHz. We have our HW configured as the figure below per the data sheet, where our VDD is 3.3V.

After doing some tests, we are able to receive data on the PICO(SPI MISO) when we try to use low speed of SPI (e.g. 0.5 Mhz, we tried 1Mhz and not always working). In our application, we try to improve the performance as much as possible, could you tell me the valid operational range of the SPI speed for our setup?

Thank you,

  • 0
    TI__Guru* 91166 points

    Dear Bin - 

    Thanks for the post and welcome to E2E. 

    The maximum for the clock speed depends on your connectivity scheme. I tested this personally with short runs all the way up to 16MHz, but if using "maker style" breadboard jumper wires between the part and the MCU, I would not recommend going above 1MHz. 

  • 0 in reply to Josh Wyatt
    Prodigy 10 points

    Hi Josh,

    Thank you for your reply.

    So the possible speed will be really dependent on our HW design, the only way to get the proper speed is to do trails with different speed, right?

    Currently, does TI have any information/document for how to make this deterministic and characterized? (for example, max  SPI speed value VS the resistance value between the SIO and the MSIO of the MCU lines)? 

  • 0 in reply to Bin Wei
    TI__Guru* 91166 points

    Dear Bin - 

    The device is capable - here you are asking about the physical interface.

    This application note discusses layout guidelines for high speed communications https://www.ti.com/lit/an/scaa082a/scaa082a.pdf  and this application note discusses the this topic in the context of why to use LVDS interface parts when using SPI, for longer distance transmission. https://www.ti.com/lit/ug/tidued8/tidued8.pdf 

    The max speed also will depend on your controller. Section 4.2 of this application note covers one example, using an MSP430 MCU. https://www.ti.com/lit/an/slaa734a/slaa734a.pdf

    I made an Ardunio style project to test this out when the part was new. (this was with a Mega2560, so your clock divide by ratios will be different)

    If you wanted to test out, you could apply this same idea in your setup, comment in/out as desired, works and recompile to test. 

    You can see the note I made myself when i ran into issues using quick setup with 6" jumper wires that were not twisted or dressed in any special way.