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PGA305: TADC Gain

Jourdan Stephane
Prodigy 30 points
Part Number: PGA305

Hi Scott,


I am currently working on the PGA305 and  I am both reading & writing EEPROM correctly (good news ;-) )

Unfortunately, I have still an issue with output signal and I think that my error comes from PADC GAIN & TADC GAIN

For example, Here are my settings to only read internal Temperature :

DAC_CONFIG = 0x00 (Absolute)

 T_GAIN_SELECT = 0x02 (5V/V + no inversion)

TEMP_CTRL = 0x43 (Internal temperature + OFF)

TEMP_SE = 0x00 (Single ended)

coeff. H1 = 0x200000 = 0.5

All other coefficients = 0x00000000

TADC= 0x1CFFB9 = 0.57 V (21.78 °C)

TADC_GAIN = 0x32DCD5

TADC_offset = 0x000000

DATA_OUT expected = DAC_GAIN (H1*TADC*TADC_GAIN) = 4*(0.5*0.57*1) = 1.14 V

but results are very different, output signal is unsteaddy, see oscilloscope results:

Waiting for your feedback regarding my results...Is there any tests to perform?

Regards,

Bastien

  • 0
    TI__Mastermind 31655 points

    Hi Bastien,

    Your TADC_GAIN value is very high. The number in TADC_GAIN is directly used as the gain, so I would expect it to be set to 1 most of the time. This is likely causing large fluctuations in the output with minor changes to the temperature. Does the output appear to respond to temperature like you would expect? If you place your finger on the PGA305 device does the output increase?

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Prodigy 30 points

    Hi Scott,

    Thanks for your feedback. There was a misunderstanding from our side aout  the Gain value (T & P).

    We though it was a coefficient coded on 3 Bytes like ho, h1, etc. .

    We had fit the coefficent to 1 and it xorks well.

    Kind regards

    Stéphane