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ADS1281EVM-PDK: Why is GPIO3 high? - I want Bipolar mode.

Part Number: ADS1281EVM-PDK

Why is GPIO3 high? - I want Bipolar mode.

I have the ADS1281 EVM PDK kit.

I'm using it in Bipolar +/-2.5V mode.

I've discovered on the ADS1281 EVM that GPIO3 is high, which (post inverter U8) is disabling the Regulator and shorting the ADC AVSS line to 0V.

(This is destroying my external VA power (+/-5V) and reference (+/- 2.5V) - actually it is destroying my -5V - which then upsets my -2.5V REF).

GPIO3 is controlled by something on the MMB0 PCB. Rev D 2009. Bom Rev F.

I feel that the MMB0 must sense the -5V rail (Bipolar mode) and set GPIO3 low. Or is it something else?

How do I get GPIO3 to go low? Have I got a link missing?

I'm using external supplies for +/-5V VA analog and an external 5V digital. I don't have J13A (+VA to 5V) or J13B (+5VA to 5V) link installed. My MMB0 layout doesn't match the manual and the manual isn't very clear on the correct way to set these two.

Thanks

Peter Baxter

  • Hello Peter,

    Do you have the ADCPro software and successfully connected to EVM from the GUI before applying the various bipolar supplies? The MMB0 needs to sense the HW through the GUI before it can set GPIO3 low to "enable" the system. The MMB0 version shouldn't matter as all the signals that go to the header are the same between the other revisions. If you are hesitant about how it is physically connected, feel free to send a picture but I'm confident we need to connect to the GUI first.

    Best,

    -Cole

  • Hi Cole,

    Thanks for responding. The information was useful.

    As I need more certainty upon system start-up.....

    I removed U8 (the Inverter) and added an 0R 0603 resistor between pin-5 and pin-4. Very easy to do.

    This now ensures I always start up in bipolar mode.

    ------------------

    Just on my last part....

    I'm using external supplies for +/-5V VA analog and an external supply for the 5V digital.

    I don't have J13A (+VA to 5V) or J13B (+5VA to 5V) link installed.

    My MMB0 layout doesn't match the manual and the manual isn't very clear on the correct way to set these two. There is no schematic either.

    Might you be able to tell me the appropriate way to set these two links?

    Thanks

    Peter Baxter

  • Hi Peter,

    Not sure if you've found the MMB0 schematic, but I found it on this post: https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/775258/faq-what-documentation-is-available-for-the-mmb0

    Your goal is to make sure you're powering the device and MMB0 externally correct? I believe you're doing it correctly. You want to separate +5VA, +VA (+10V in the user guide) from the +5V or +5VDC, then you remove those jumpers. But you'll still need +5VDC to supply the voltage to the actual MMB0 board so it creates +1V8VD and +3.3VD. 

    Feel free to cross reference with the schematic and let me know what you think.  

    Best,

    -Cole