ADS1282EVM-PDK: External Voltage Reference

Hi Karam Shanti,

Thanks for your interest in the ADS1282EVM, we will need some additional time to respond to your question. Please expect a response early next week at the latest

Thanks for your patience

-Bryan

Hi Bryan,

Any updates on the response? 

Hi Karam Shanti,

Yes, we will reply by the end of the week

-Bryan

Hello Karam,

Thank you for your patience. Can you please send a drawing (sketch) that shows how you have the EVM configured, using external power supplies, and the grounding between your external voltage source and the EVM ground?

If you have the EVM configured for bipolar operation (-5VDC connected to -5VA, J14, MMB0), then the maximum voltage allowed on the REFP or REFN inputs will range from -2.5V to +2.5V.  Connecting a 5V reference to REFP and ground to REFN would cause errors with the ADC operation, as an example.

Regards,
Keith Nicholas
Precision ADC Applications

Hi Keith,

I took some pics of my current EVM configuration so hopefully those will suit you better.

(current lab setup: black = GND. red = power) 

(power supply: black wires from power supply are connected to the white GND wire from J14)

(green breakout board is external voltage reference. blue wire is GND, green wire is output for voltage reference (2.5V), red is power line for voltage reference)

(power terminals: red = -10V, purple-1 = +10V, purple-2 = -5VDC, yellow +5VDC. white, GND)

(voltage reference on J6A: yellow = 2.5V output on EXTREFP, white = GND for EXTREFN

(jumper configuration MMB0) 

Best,

Karam

Hello Karam,

It looks like the EXTREFN connection is not connected to ground.  Looking at the pictures, it appears to be connected to J8, VD1, which is a floating pin.  Please connect the EXTREN pin (white wire in the picture below) to a ground  (Can connect to the DGND pin on J8).

Also, please measure the voltage on the EXTREFP pin relative to the board ground and verify that it is 2.5V expected voltage.

With these long wires, you will not get good performance, but the board should function.

I also noticed in your power supply connections that the -10V is connected to ground.  This is O.K. to get the board functional, but the input amplifiers will require a -10V supply on this pin in order to meet typical performance.

Regards,
Keith

Hi Keith, 

So I moved my white wire to DGND and I verified the EXTREP pin relative to the board ground and ended up getting around 2.50V. But ADCPro still keeps giving me the same error. Also about the -10V, how would I go about safely applying the -10V power source with my current power supply?

Best,

Karam

Hello Karam,

Your lab supply is a triple output supply, so should be capable of +5V, +10V, and -10V.  I suggest looking at the user's guide for your power supply that shows how to generate 5V and a bipolar +/-10V configuration.

Regarding the ADS1282EVM, there appears to be an issue with the drivers on Windows 10 and 11.  We will need to fix this in order for the EVM to work.  Right now, I do not have an estimate when we will be able to address this issue.  This software should run on Windows 7 if you need to get this working sooner.

Regards,

Keith

Okay I was able to get the -10V line working. And in terms the drivers, I'm running a Windows 7 and everything works fine when I'm using the internal voltage reference. My problem is when I'm using a external voltage reference, ADCPro starts timing out or it asks me to do a hardware reset which doesn't resolve the problem. I'm currently using a external 2.5V voltage reference, using pins EXTREFP for the +2.5V and GND for the EXTREFN. Is there a specific range for the external voltage references I can use? Also I've been working on this board for a while and I still haven't gotten a clear response as to why I can't get the external voltage reference to work. Is there another software or microcontroller I could use along side the board to make it work? I was planning on using the MSP-EXP430FR5969 development kit with the ADS1282EVM after I got the ADS1282EVM, that's why I'm asking if there are other alternatives to get around this software problem. 

(internal 5.0V voltage reference)

Hello Karam,

Since you are able to get this to work with the internal reference, then I do not think this is a software issue.  The external reference can range from 0.5V to 5V when using unipolar mode, and should have no effect on the operation of the software.

If you could provide a sketch of your exact setup with external reference, this may help.  It is hard to tell from the pictures the exact connections that you have setup.

Are you still able to get the board to work with the internal reference?

Can you measure the +5V supply to make sure that it is still correct?

I am also trying to get an EVM working in the lab (I do not have Windows 7 to quickly test), and once I do, I will confirm the system with an external reference.

You can use any MCU that has a SPI port, but you will need to write the software to get it running; we do not have any sample code for this part.

Regards,
Keith

Yes I am still able to get the board to work with the internal reference and I get about 5.12V for the +5 supply. So all that looks good. And here's the schematic:

And I see, I'll wait for your results with the external reference on the board then. 

Best,

Karam

Hello Karam,

I have not been able to get the software working on WIN 10/11.  However, I think I have another option that should work better.

Since you are using an external reference, connected by cables, this will pickup quite a bit of noise and may be part of the reason that your board does not work correctly.  Instead of connecting the external reference directly to the ADS1278 reference inputs, you can use the reference buffer included on the EVM board.

Remove the jumper on J1, and directly connect your reference positive +2.5V side to the OPA IN (middle pin 2) and the ground connection of your reference to the GND terminal (pin 3), as shown below.  This will use the on-board reference buffer as well as an input filter, which should provide much better performance.

In order to use this configuration, you will want to set the reference switch back to the ON-BRD setting.

Regards,
Keith

Hi Keith,

I tried that and I'm still getting the hardware rest error. I verified that the internal voltage reference still works after this though and everything still seems to be working fine (when using internal voltage ref). 

Best,

Karam

Hello Karam,

I suggest using the internal voltage reference to verify basic system functionality and then design a board with the exact configuration you need in your application.  With the long wires, you may be picking up enough external noise to cause communications issues with the EVM.

Unfortunately, there is nothing else I can think of to help you with your debug of the system at this time.

Regards,
Keith