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ADS1292R schematics design, questions about pins

Other Parts Discussed in Thread: ADS1292R, TPS730

Hello all,

I have couple of basic questions related to the schematics of ADS1292R (can be found from user´s guide of demo kit).

1) Which pins are absolutely nessessary to be connected to microcontroller besides SPI connections? I understood at least DRDY should be connected but there was some other option for START and PWDN/RESET? Can these two be command just via SPI? If yes, does it decrease performance or why there are individual leads for these two? For my application it is very important to avoid any extra leads, that is why these questions.

2) I am not going to use RLD, GPIOs, or external clock. Is it ok to float RLDOUT, RLDINV, RLDIN/RLDREF, CLK and CLKSEL pins? I understood that GPIOs should be connected to the ground through resistors shown in example schematics (R32 for GPIO2 and R34 for GPIO1). Is this correct? Should I connect VCAP1 and VCAP2 like they were in example schematics?

3) In schematics, AVSS is analog ground. How about used common ground symbol, is that for digital ground?

4) In example schematics there have been used two different voltage regulator (TPS73033 and TPS73201) for generating analog and digital power supplies. Why it was decided to use both when (in my opinion) either of them would have been suitable for both cases?

Thank you!

BR,

Katariina

  • Hey Kateriina,

    In general, a lot of what you ask here is treated in the datasheet for the ADS1292R. In the future, I'd ask that you check that document for answers before posting on the forum: www.ti.com/.../ads1292r.pdf

    1) START can be tied low in the hardware and they you can start the converter using the START command and stop them using the STOP command. You can hold PWDN and RESET high in hardware and use the RESET command. Neither of these affects performance. It just affects the logistics of how you use the part.

    2) All pins related to the RLD can be floated. You must tie the CLKSEL pin high in order to use the internal clock. Details on how the clock works can be found in the datasheet. The CLK pin itself, however, can be floated if you don't care to use that clock output. For the VCAP pins, look to pages 60 and 61 of the datasheet.

    3) I believe so.

    4) There are a few reasons. Having different regulators supply different parts of the circuit is called "point-of-load" power delivery which has several advantages versus using one regulator. The TPS730 was used because this board was originally intended to have Bluetooth functionality and that regulator is a regulator for Bluetooth chips.

    Regards,
    Brian Pisani
  • Hello Brien,

    1) I am only asking what to do with START and PWDN/RESET physical PINS so person with software can handle my schematic design.
    - When I am placing these pins, my options are ground, float or connect to "x" (in this case microcontroller).
    - Does "tie low" mean grounding? How about hold high - is that floating?
    - So am I correct, that these can be command via SPI and thei don't need own connection to microcontroller? Yes / No.

    2) Your answer is why I asked. Datasheet says that if RLDIN/RLDREF and RLDINV are not used, those should be connected to AVDD. On the other hand there is no instructions for RLDOUT. But your recommendation is to float them all. So taking your (outside of datasheet) advice I can make my layout design just little bit easier.
    - When my options for pin are ground, float or connect to "x", what do you mean with "tie the CLKSEL pin high"?

    3) Actually page 60 shows one example, where now all grounds are with the same symbol. But maybe I can handle this.

    I did read tha datasheet (and forum questions) many times indeed. These were the questions I had in my mind afterwards. So sorry for wasting you time!

    BR,
    Katariina
  • Hey Kateriina,

    I'm sorry if I came off as abrasive! Please forgive me.

    1) Low means tie to ground and high means tie to DVDD for digital pins. Yes reset, start, and stop can be controlled by commands. You cannot power down the device by command, but you can put it in standby mode which keeps only the reference powered.

    2) You can tie RLDIN/RLDREF and RLDINV to AVDD or float them. Those connections are not of critical importance if not being used. The RLDOUT pin must be floated if not being used since it is an output. An incorrect register write could create a short circuit if the RLDOUT is tied to another potential. For CLKSEL, I mean connect to DVDD.

    3) Sorry I was referring to the section beginning on page 60. On page 61 there is a diagram showing the configuration for bipolar supplies. I wasn't sure which supply configuration you were using.

    Regards,
    Brian Pisani