PGA970: PGA970

Hi Ran,

Ran Litver said:

1. Concerning its linearity: it is said 0.01% FSO for a channel I belive. I am more interested on the raitimetric linearity. Can you provide this value?

I'm going to assume ratiometric linearity is the same defined in this application note: https://www.ti.com/lit/pdf/slyt680 

As such, I cannot provide this value as it relies on the user to write firmware and develop a formula based on this idea. Nonlinearity in the 0.01% of FSO context is simply an uncorrelated error source that is inherent to the modulator. It cannot be corrected or calibrated out. Ratiometric linearity is a concept that takes a system, and for example, relates the coil excitation source to coils position. This is an attempt to reduce error in the system so that the system is more accurate, so I'll call this accuracy from now on.

TI doesn't know what kind of LVDT is connected to the input, and doesn't know what kind of calibration routine will be written. As a result, we characterize the device so that only inherent, noncorrelated errors can be added together to show what your best case error value will be.

To contrast, can take the PGA305 for example, which is a similar fixed function device for resistive inputs instead of LVDTs. TI wrote the algorithm so we have accuracy values after calibration written into the datasheet specifications. This is the value you are looking for for the PGA970 but we do not have such a value.

Ran Litver said:

2. FSO: what is the "O" stands for?

FSO is Full Scale Output in relation to the DAC.

Ran Litver said:

3. I expect to get much higher linearity when using 24 BIT ADC (or even 15BITs of ENOB)

I'm not sure if there's a question here but it looks like you are concerned with the Ratiometric linearity or accuracy. The 15 of ENOB is the sum of amplifier noise, reference noise, SDM noise, and quantization noise. There are plenty of 24 bit delta sigma ADCs with better noise performance but we expect the user to use the output DAC which is 14 bit resolution (ideally). This means we know the noise of the front end and ADC will not significantly contribute to the DAC's output noise performance. 

I see this as the integrated solution performance vs. discrete performance. If you want more accuracy, you might want to split out the ADC, DAC and processor, but the PGA970 gives everything in one package. For many customers, the accuracy is good enough for them in context of the 14 bit DAC output that comes with the device.

Ran Litver said:

4. I need the whole setup to verify my LVDT parameters. I want to use the specific evaluation board of the part.

a. Can you please specify what else besides of the evaluation board I need (hardware ans software) 

b. Does the sine wave information is already in the RAM or I will need to load it? 

c. etc

The evaluation board should be good enough to get you started. If you have access to the datasheet, then you have access to the GUI which can help with basic functions. For the sine wave generator, you will have to set the settings in the GUI and click "generate RAM table" to get the exact values that will be need to load into memory on power up.

Other than that, the PGA970 has the ARM M0 Core and requires firmware to run anything more specific. You also have access to example code if you have access to the datasheet.

Ran Litver said:

5. How can I get all I need from you?

If you have access to the datasheet, you have access to everything that TI will provide. I'm happy to answer any questions you have about the device, just know that I cannot help with Firmware questions.

• [FAQ] What is the E2E support model for the PGA900 and PGA970?

Best,

-Cole

Thank you very much for your detailed answer and best support!