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PGA305: PGA305

Francisco Requena
Intellectual 410 points
Part Number: PGA305

Hi Scott

I'm playing with these T and P gain and Offsets and other parameters and I'm a bit confuse. The confusion I have is as follow:

1.- I can record PADC and TADC using digital interface with no problem. when I apply the temperature equation to get T in degrees Fahrenheit  it works very good.

2.- when I use TGain = 1 and TOFFSET =0, same for Pressure,  I expected to get same output for temperature and pressure  when using the COMBUF registers. but they aren't close and they vary alot.what could be happening?

3.- I saw that the H0EE and  G0EE are calculated by multiplying the actual H or G for 2 ^22. how does this apply to TADC and TOFFSET? 

4.- what format needs the be pressure and temperature after the ADC to input the TC and NL algorithm? I mean, is signed integer the correct output after the TADC and TOFFSET asre applied to TADC (same for Pressure)?

5.- from question 4, when Im using internal temperature the temperature T = (1/6636.1) *TADC - (1710281.3/6636.1). is TGAIN = (1/6636.1) and TOFFSET = (1710281.3/6636.1).

I'll continue to dig in to this tomorrow , but I need a good guide on these PGA Calibration parameters calculations.

Please advice 

  • 0
    TI__Mastermind 31655 points

    Hello Francisco,

    2. What are the analog gains you are using, and what are the inputs? The output is of course going to depend on the inputs to the PADC and the TADCs. If you are using the internal temperature sensor, the gain is forced to 5V/V, while the PADC gain could be set to something different. The digital Tgain and Pgain and offset are just applied afterward in the compensation algorithm.

    3. All of the inputs to the compensation algorithm are normalized by 2^22, so the equation (equation 6) given in the datasheet shows the correct way in which the coefficients are applied. All of the coefficients are stored this way, including the TADC gain and TOFFSET.

    4. The input to the algorithm is the output of the ADC, which is a signed 24 bit number in 2s complement format.

    5. The equation you are showing is the relationship between the physical temperature in degC and the TADC code. This isn't related to the temperature compensation.

    Regards,

  • 0 in reply to Scott Cummins
    Intellectual 410 points

    Scott

    Thanks by the quick response, I getting close reading the COMBUF register without issues but I still have question on  this device  compensation engine:

    1.- From the Datasheet I understood that the input P and T to the Tc and NL engine is gain and offset corrected P and T. if this is true then I have to apply the Gain of  (1/6632.1) and and offset of (1710281.3/6632.1) when i'm using the internal temperature of the device. 

    2.- how this normalization works? from the datasheet i see that G0EE = G0 * 2^22 if I apply this concept for the TOFFSET =  (1710281.3/6632.1) it give me an unreasonable number that wont fit the sign 24 bits format.

    please advice

  • 0 in reply to Scott Cummins
    Intellectual 410 points

    Hi Scott

    I manage to debug my firmware to get the correct PADC and TADC thru the COMBUF registers, but I have these issues remaining to start doing testing:

    1. I can't get any value on Compensated COMBUF using the TI project board neither my design even changing PADC_GAIN and PADC_OFFSET, same for TADC's Gain and Offset. perhaps there is some conditions the parameters i entered are  not fulfilling to make the compensation portion works? 
    2. I do have my own coefficient calculators that I need to adjust to the PGA requirements or formats. 
    3. Perhaps my confusion is that I'm expecting to feed the Tc and NL engine with uncorrected pressure and temperature using the digital Gains and Offsets, if that is not the case please provide me with the correct procedure.

    Please advice 

  • 0 in reply to Francisco Requena
    TI__Mastermind 31655 points

    Hi Francisco,

    As I mentioned, the equation that you are referring to only correlates the physical junction temperature to the TADC code. Unless you are using the PGA305 to output a temperature measurement as well, the absolute temperature value in degC is irrelevant to the compensated pressure output, so there is no need to account for the modeled gain and offset of the temperature sensor's output by using the digital gain and offset correction.

    For the COMBUF page on the PGA305EVM to work properly, the PGA305 must be placed in compensation mode. Please make sure you do not have it set in digital interface mode.

    The digital gain and offset are applied before the TC and NL correction.You can see this in the Digital Gain and Offset section in the datasheet (7.3.19.1). The purpose of these is to account for offset that was not corrected for in analog and to fill out the range of the ADC if the analog gain was not set properly. Ideally the digital gain should always be 1 if your analog PGAIN was set correctly.


    Regards,

  • 0 in reply to Scott Cummins
    Intellectual 410 points

    Hi Scott

    I'd like to finalize this unusually long conversation about this device PGA305. There is an issue remaining that make it unusable for our need, this one is related to the inability to use the Tc and NL compensation engine.

    We have tried using  the EVM board to produce a calibration and obtain the  COMBUF Pressure compensated output, but we can not get it despite of reading the PADC and TADC correctly thru the COMBUF.

    Can you send me an example using the EVM board that produces Compensated COMBUF output diferent than ZERO?

    Please advice....

    P.S: my email changed as company name has change.

  • 0 in reply to Francisco Requena
    TI__Mastermind 31655 points

    Hi Francisco,

    If you are reading a 0x0 output on the DATA_OUT of the COMBUF, the reason is most likely due to a CRC error. 0xFFFFFF is reserved for an AFE diagnostics error.

    First I recommend rechecking your CRC to make sure it has been updated to match your latest EEPROM settings. If the problem persists, I would also adjust the AFE diagnostics. I would start by turning everything off. You can see some settings that achieve this in the capture below. Make sure you also set the AFE bit mask configuration to 0x00 alongside turning the Diagnostics Enable to OFF.

    Regards,