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PGA309: PGA309 lookup table question

Eyal Bortman
Prodigy 30 points

Part Number: PGA309

Hi

we are using the PGA309 in a force sensor application . we were wondering if the PGA309 is capable of performing extrapolation beyond the built in lookup table

since the application temperature operating conditions exceed the calibration temperatures points  .  We are calibrating at -10 to 40 degrees C while the application is working between -20 to 85 degrees C

we were wondering whether the PGA will continue to extrapolate the gain and zero DAC based on the measured temperature or whether the gain and zero DAC will remain constant once

exceeding the maximal or minimal calibration temperature points . In addition , we would like to know what will be the most cost effective way to update the look up table such that the

operating temperature will be reflected in the table ?

  • 0
    TI__Mastermind 19710 points

    Hi Eyal,

    The PGA309 temperature lookup function works as follows:

    Let's use an example with 3 temperature points, described by the following ADC values:

    T0 = 0x0000

    T1 = 0x0140

    T2 = 0x01E0

    For temperatures whose ADC codes fall at or below 0x0000, the G0 and Z0 values are used.

    For temperatures with ADC values from T0 to T1 (0x0000 to 0x0140), Gain and Offset will be linearly interpolated using G0 and Z0 and the GM1 and ZM1 slope factors. At T1, the gain and offset DACs will be at G1 = G0 + (GM1 * (T1-T0)/256) and Z1 = Z0 + (ZM1*(T1-T0)/256).

    Between T1 and T2 (0x0140 to 0x01E0), a similar interpolation is performed, this time using GM2 and ZM2, up to a maximum of G2 = G1 + (GM2 * (T2-T1)/256) and Z2 = Z1 + (ZM2*(T2-T1)/256). 

    Above T2, since there are no further entries in the lookup table, G2 and Z2 still apply. 

    The PGA309 will re-read the lookup table from EEPROM following each Temperature ADC conversion. If Continuous Convert mode is not enabled, and no conversion is requested by writing a 1 to the ADCS bit (Register 6 Bit 12), the last ADC result will be used instead. This ADC result is then used to select an appropriate entry from the lookup table. 

    To calculate the values for the lookup table, you'd need to follow the procedure described in section 3.2 of the PGA309 User's Guide (SBOU204B).

  • 0 in reply to Alex Davis
    Prodigy 30 points

    Hi Alex

    Thank you for your valuable feedback ! so just to make sure that I have a complete resolution for my question , please confirm the following :

    The PGA309 will not perform extrapolation beyond the prescribed temperatures in the lookup table and in a scenario where the read temperature is out of range of the lookup table
    the gain and zero DAC will remain constant and will not extrapolate .

    Thanks  

  • 0 in reply to Eyal Bortman
    TI__Mastermind 19710 points

    Hi Eyal,

    That's correct.

  • 0 in reply to Alex Davis
    TI__Genius 11135 points
    Eyal

    We haven't heard back from you so we assume this resolved your issue. If you need additional help just post another reply.

    Thanks
    Dennis