ADS1278EVM-PDK: Designing an IEPE excitation source for the ADS1278V2EVM evaluation version

Hello,

If you want to interface an IEPE sensor to the ADS1278, then you will need the full input signal chain used in the IEPE sensor design, including the fully differential amplifier to drive the ADC inputs.  If using the ADS1278V2EVM, then channels 1-4 already include this amplifier, so you would not need to duplicate this if using the EVM for initial system evaluation.

The full design files for the IEPE reference (TIDA-010249) are available at the below link:

https://www.ti.com/tool/TIDA-010249

Regards,
Keith Nicholas
Precision ADC Applications

Thank you very much! Can you provide more information? I know relatively little about this and if you could provide me with more help it would save me a lot of time!

Hi keith, thank you very much for your help! I have designed the circuit again, I have designed the IEPE excitation source circuit and the fully differential amplifier circuit; the circuit diagram is below:

For channels 1-4 I simply connected the LEX line of the IEPE excitation source to AINP of the ADS1278EVM; the signal to be measured is input from AINP_SMA of the ADS1278EVM;

For channels 5-8 I connected the IEPE excitation source circuit and the full differential amplification circuit together, and connected the outputs AINP, GND, GND, and AINN to these pins of the ADS1278, and the inputs to be measured were input through J9;

Here's my overall schematic, and I'm going to hit two identical PCBs for the 8 channels;

Since I know very little about this before, I would like to ask you to confirm this before I hit the PCB, and I would be very grateful if you could check this for me!

Hi, Keith. Thank you very much for double checking, this is indeed a very serious error.

(I have a 5V power supply, but I don't have a 24V power supply; moreover, since I don't know enough about this part, I try not to change the circuit too much to avoid bringing more uncertainties)

I have corrected both errors and when I did another check I found a new problem:
In the TI-010249 program, the VCM pin here should be connected to ADS12L11, but the circuit I designed does not have this pin;

I checked some information:
The datasheet for the ADS127L11 shows that: the VCM pin provides a buffered output voltage at the midpoint of the AVDD1 - AVSS supply; AVDD1 = 5V and AVSS = DGND, so the input to the VCM should be 2.5V; it also says that the VCM can be left off;

So I'm asking: can I remove this part of the circuit? If not how do I design this part of the circuit?

Thank you very much!
I wish you all the best!

Thank you very much! I learned a lot!
Have a nice day!

Hi, keith! Thank you very much for the help you gave me before, unfortunately now I have a new problem.

As you can see in the picture below, I did a PCB punchdown of the schematic we discussed.
It ended up looking like this:

But when I connected 5V power to it, white smoke was generated at pin U17 and I immediately disconnected the power.

I have investigated this situation, and found a mistake: U17 is sot23-6 package, I did not understand it clearly, so it led to the patch paste the opposite; well, I found the phenomenon is not normal after I power on and power off, but I'm not sure whether it will have an impact on other components?

Now I have re-pasted the new U17, but it is still not right: when I give it J1 and J3 at the same time connected to the 5.2V power supply, its two lamps do not light up, and sometimes there is even a "hissing" sound, using a multimeter to measure the TP10 it does not output a voltage of about 24V.

I have now patched two boards and they have the same phenomenon. I have double checked the soldering and there is no soldering.

Could I possibly have a power supply problem? I've used two power supplies to try: one is an adjustable DC regulated power supply (the vendor says it's in constant voltage mode and automatically adjusts the current according to the load; I've used it to power my ADS1278 evaluation board just fine at 6V500ma), and the other one is a 5V power supply (a multimeter goes directly to the current and measures it at about 5Ma); they're both the same phenomenon.

Where is the error that caused this situation? Can you give me some help?

Sincerely
Have a nice day

Altium_0608_IEPE++_2024-06-20.zip

Hello,

I am out of office and will reply on Friday, June 21. 

Regards,

Keith

Hi, keith! 

I found a few things by troubleshooting myself:

1. The reason the two diodes don't light up is that I put them on backwards

2. TP11 is normal 5.01V; but TP5 is about 16V, not normal 24V;

3. There will be a hissing sound, I check the information seems to be the L2 power inductor whistling

4. U17 will have white smoke

So the problem should be in L2 and U17, I have placed an order for a new device, can you help me to see if there is any design unreasonable place?

Sincerely
Have a nice day