ADS1262: ADS1262 with 10V Excitation

Hi Thomas,

First off, welcome to the TI E2E Forums!

There are two things that come to my mind to consider for 10V excitation:

1. The ADC's input common-mode voltage
   To ensure that the input signal is within the ADC common-mode range you'll need to generate a positive and negative excitation voltage, centered around mid-supply. By generating a bipolar excitation voltage, you won't need any additional signal conditioning on the inputs to level-shift the signal.
   
   For example, if AVDD = +2.5V and AVSS = -2.5V, exciting the load cell with +/-5V rails will keep the differential input signal centered around 0V.
   
   Similarly, for AVDD = 5V and AVSS = 0V, the positive excitation voltage should be about +7.5V and the negative excitation voltage about -2.5V, so that the differential input signal is centered around +2.5V.
   
   
   
2. The ratiometric reference voltage
   Typically, the load cell's excitation voltage is also used as the ADC's reference voltage to make the measurement ratiometric. When the excitation voltage is 5V or less you can feed it directly to the ADC. However for 10V excitation, you'll need to divide down the excitation voltage with a resistor divider before routing it to the ADC. If you created the bipolar excitation voltage (from consideration 1), then the reference voltage should also be within the correct input common-mode range.
   
   Also, I would recommend that the signal inputs and reference inputs be designed with matching filters. This ensures that the excitation voltage noise will be common to both inputs (across the frequency spectrum) and results in better noise cancellation. Reference: http://www.ti.com/litv/pdf/sbaa201.

Best Regards,
Chris

Thanks for the extensive post!   Seems as straightforward as I originally thought.  Do you have any suggestions on a high stability 10V Reference IC that you would recommend?   Also, the customer is saying they want the option for both 5V and 10V Excitation (software toggle), so I am guessing I will have to add in another switch with multiple voltage dividers.  Since I am limited on the GPIO on the ADC, I plan on toggling it from the controller.   Do you also have any suggestions on a 10V capable analog switch?

Hi Thomas,

I'm not the voltage reference or analog switch expect, but I'll do my best to help or see if I can find some else who is more of an expert in this area...

What is the expected impedance of your bridge sensor?
You'll want to know the minimum impedance so that you know how much current the reference needs to source. Keep in mind that the smaller the bridge impedance, the more power the bridge will need to dissipate. You'll encounter self-heating errors if the bridge is not able to dissipate this heat.

For analog switches, I'd probably start with these devices: http://www.ti.com/lsds/ti/switches-multiplexers/analog-switch-products.page#p1143=1:1%20SPST;1:2%20SPDT;1:4%20SP4T&p480=1;8&p106max=10;18&p1498=Catalog

Another alternative option might be to use a DAC to excite the bridge and avoid the need for multiple voltage references and analog switches. Something like the DAC7760 might work since it can drive up to 30 mA, though it probably has more bells and whistles than you need.

Best regards,
Chris