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2 questions about DDC232

zazza
Prodigy 50 points
Other Parts Discussed in Thread: DDC232

Hi to all

I'm designing the new version of a 64 channels photodiode board using the new DDC232 ic.

1) There's a new pin called QGND,  the datasheet says: "The QGND pin should be treated as a sensitive analog signal and connected directly to the supply ground with proper shielding." What does this means? Should I connect it to the same ground plane where I'll connect together AGND and DGND, or must it connected to the common kathodes of the 64 photodiodes array?

2) In the new application I would like to make interlaced integrations, where the first is 10 times shorter than the second (for instance 100us followed by 1ms), without losing integration time. I'm not sure if this is possible, since it's more likely a NON-CONTINUOUS mode, and in this mode only two short and equal integrations seems to be allowed, loosing integration time. I'hope this is "interlaced" mode can works, because I need to expand the dynamic range above the 20 bits. The idea is that If the integration made with 1ms saturate, than I'll use the integration made with 100us.

 

Thank you in advance,

Andrea

  • 0
    TI__Guru* 98215 points

    Andrea,


    1. The QGND refers to a "Quiet Ground". In general it is connected to AGND, but since this is a reference to a measurement, you must be careful with how this is connected. For a schematic point of view, refer to Figure 3 in the datasheet. QGND is the ground connected to the positive input of the opamp of Integrator A.

     

    2. In the case of doing to measurements of about 100us, I think you will lose integration time if you go that fast because you would still have to go into non-continuous mode. There will be a delay after the the two m/r/az cycles as you come out of non-continuous mode as in Table 5, and go into continuous mode as in Figure 16.

     

    If you still want to do a fast and slow measurement, it's still best to stay in continuous mode. The fastest you'll be able to do this if given in Table VI where it shows the timing for operation in the continuous mode (162us) but it's still better than coming out of non-continuous mode.

     

    Joseph Wu

  • 0 in reply to Joseph Wu
    Prodigy 50 points

    Dear Joseph, thank you very much for your super-fast answer!

    The 162us timing could be sufficient, but it's referred to the HighSpeed mode of the DDC232, available only on CK version.

    Althought the datasheet have some (not all) specifications on this higher speed version, the order code is missing as well as in the TI product page.

    I suppose that this version doesn't exist, could you give me some informations?

    We have in mind a slightly different application where we could need to integrate continuously up to 6kHz.

    Thank you again,

    Andrea

  • 0 in reply to zazza
    TI__Guru* 98215 points

    Andrea,

     

    I checked with the development group and the CK version should be available within a few weeks (as orderable). Sorry, but I didn't realize that it wasn't available yet.

     

    Joseph Wu

  • 0
    Prodigy 20 points

    Hello Andrea:

     

    I am looking for a high resolution photodiode borad. Is your old version ready to use? I have 16 diodes but I need then to be sampled at exact the same time.

     

    Thank you for your help

     

    Simon

  • 0 in reply to Simon Li48026
    Prodigy 50 points

    Hello Simon,

    Unfortunately our boards are for internal use only, on our machines, so I can't help you.

    Best wishes,

    Andrea