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PGA900EVM: Connecting an external bridge with the PGA900EVM + Calibration

Tobias_1
Prodigy 40 points

Part Number: PGA900EVM

Dear Sir or Madame,

I have a PGA900EVM and would like to connect an external bridge instead of the built in bridge. My idea would be to open Jumpers J1 - J3 and to connect my own bridge there. See Screenshot from EVM User Guide (p. 4):

My Questions:

1) Is it possible to connect an external bridge to the EVM? If yes, where to connect VBRGN of the external bridge? To Test Point 37 of the module?

2) How can I realise the calibration of the system for a 4 - 20 mA output signal, is there somewhere a step by step description? I couldn't find one in the documentation (I went through PGAxxxEVM-034 User Guide and PGA900 Data sheet)

3) Same as 2) but for 0 - 10 V output

Thanks in advance and best regards

Tobias

  • 0
    TI__Mastermind 31655 points
    Hi Tobias,

    1. Yes, you can connect an external bridge to the the EVM. You will first need to open the jumpers J1, J2, and J3 as you mentioned. VBRGP is TP38, VBRGN is TP37, VINPN is TP35, and VINPP is TP34.

    2. In order to calibrate a sensor you will need some firmware programmed into the integrated M0 microcontroller with a compensation algorithm. Since the PGA900 does not have any firmware programmed on the microcontroller you will need to develop some to try calibrating a sensor. You can find some generic reference firmware here: www.ti.com/.../toolssoftware to get you started. Or you can take a look at the PGA300 or PGA305 which integrate TI's linearity compensation algorithm.

    Regards,
  • 0 in reply to Scott Cummins
    TI__Mastermind 31655 points
    Hi Tobias,

    Just for further information on the PGA300 and PGA305. They are both pin-to-pin compatible to the PGA900 and all 3 devices use the same EVM. So you can easily sample any of these devices and use the EVM you already have to evaluate them.

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 40 points

    Hello Scott,

    Thanks for your answer.

    Wow, this seems to be a bigger effort than just doing a quick test with an external bridge and the PGA900.

    Unfortunately only the PGA900 in its 3.6 x 3.6 mm BGA package is possible for us. The PGA300 and 305 are only in 6 x 6 QFN package available and this is to big for our Layout.

    Regards
    Tobias

  • 0 in reply to Tobias_1
    TI__Mastermind 31655 points
    Hi Tobias,

    There are a couple of options depending on the evaluation you would like to do. To test the operation of the AFE input portion, you can leave the microcontroller in reset, and simply read the ADC values using the GUI. You can do the same with the DAC, setting specific codes using the GUI and testing the voltage or current output modes.

    If you want to connect the ADC output to the DAC input, you will need some firmware programmed in the micrcontroller to do this. The reference firmware I linked above has some additional documentation you may find useful:

    Software quick start guide: www.ti.com/.../sldu015a.pdf
    Software user's guide: www.ti.com/.../sldu013a.pdf

    The quick start guide describes how to program the firmware to your device using the PGA900EVM, an XDS200 debugger, and Code Composer Studio. The software user's guide describes the example firmware in detail.

    There is a basic 2nd order compensation algorithm included in the PGA900 reference firmware. You can calibrate using this, or you can simply program some coefficients that pass the ADC output directly to the DAC to avoid this.

    Regards,
  • 0 in reply to Scott Cummins
    Prodigy 40 points

    Hi Scott,

    okay, thanks for your answer. I will discuss with the team if we will do the firmware programming for the M0 uC, because only testing the AFE or the DAC isolated is not what we want.

    I have two more questions regarding the PGA900, but they're not directly related to the initial questions in this post, so I'll make a new post.

    Regards