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PGA302: Datasheet clarification

Ruben Khazhakyan
Prodigy 20 points
Part Number: PGA302

     Hello,

I work with pga302 datasheet and have a couple of questions:

        Q1.  In the datasheet internal voltage reference TC  specified  as +/- 250 ppm/C.

                Is this typo ? 

        Q2.  My project is - design pressure transmitter. The sensor is piezoresistive bridge. 

                Assume , the sensor is ideal .  What could be the best accuracy , that  pga302  can achieve ?

                On page 68, table 67  the numbers  look strange. E.g. VINPP - VINPN = 34.651 mV,  VOUT EXPECTED  =  0.5 V

                                                                                                       VINPP - VINPN  = 13.844 mV,    VOUT EXPECTED  =  2.5 V 

                                                                                                                  ---- 

                 I assume that gain is the same for all rows. Please, explain.

    Thank you in advance,

Ruben

  • +1
    TI__Mastermind 31655 points

    Hi Ruben,

    That is not a typo. The voltage reference temperature coefficient is shown there. You can see more information about this kind of specification here: Voltage Reference Selection Basics White Paper (Rev. A)

    The methodology for acquiring the data for tables 67 and 68 is described just above the tables in the application data section. PGAIN was set to 40V/V for the test, and a calibration was run. The input used for this test was a sensor emulator, so the inputs were perfectly repeatable, much like an ideal sensor. Given a proper calibration and an ideal sensor, you can expect accuracy similar to what is shown in the tables.

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Prodigy 20 points

    Hello Scott,

    For Q2,  above table 67 stated , that PGAIN set to 40V/V.  Then,  not clear how lower (second row vs first) input voltage (13.844 mV)  generates higher output (2.5V).  

    E.g   P1:   34.651mV x 40 x A = 0.5 V   

            P2:  13.844 mV x 40 x  A = 2.5 V

            where A - some constant, that   is the same for P1, P2 and P3

    Or  I miss something ?

    Thank you for response.

    Ruben

  • +1 in reply to Ruben Khazhakyan
    TI__Mastermind 31655 points

    Hi Ruben,

    The PGAIN only sets the gain between the input and the ADC. The DAC output is controlled by the internal temperature and nonlinearity compensation algorithm, and is not a direct passthrough of the ADC data unless it is configured that way. In the datasheet example a 3 pressure 3 temperature calibration is done, where the inputs and desired outputs are shown in the table. The details of the compensation algorithm are described in the datasheet in the Digital Compensation and Filter section.

    Regards,

    Scott

  • 0 in reply to Scott Cummins
    Prodigy 20 points

    Hi Scott,

    Got you. Many thanks.

    Regards,

    Ruben