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PGA309 questions

K.Hamamoto
Guru 12155 points
Other Parts Discussed in Thread: PGA309

Hi

We have some questions for PGA309 from our customer.

The customer are evaluating PGA309 on their board.

Please give us advice for these questions?

1.The conditions required specifications of our customers is Ta = -40degC - 125degC. 

   (Requirements less than 1% ±) Can this device ensure is to what extent accuracy in all temperature range of use?

      ( The temperature index is only 17 points. )

2. Can you give us if there is a setting example in Fine and Coarce.

3.How much the response speed does this device have?

　　　( To the output of the results from the detection) 

Please let me know if you have any question.

Regards,

Koji

  • 0
    TI__Genius 12325 points

    Koji,

    1. The accuracy of the device depends upon how it is configured. In the specification table, the values given in bold are specified over a temperature range of -40C to 125C, I've listed some of those specifications here:

    The external EEPROM is used to store up to 17 temperature coefficients to to adjust the zero DAC and gain DAC to compensate for PGA309 offset and gain drifts over the specified temperature range. The PGA309 User Guide (starting on page 63) explains this process. Because these values are dependent on the customer's system, they must determined in the application. 

    2. The PGA309 Users Guide ( http://www.ti.com/lit/ug/sbou024b/sbou024b.pdf ) has detailed explanations of course and fine offset adjust (see page 24). Course offset adjust is implemented before the front-end PGA and should be adjusted before the fine offset adjust. It can be adjusted in steps of Vstep = Vref/1200, and has a range of Vstep * 2^4 in either polarity. Any residual offset that cannot be removed by the course offset must be removed by the fine offset adjustment implemented by the zero DAC. After adjusting the gain DAC, the zero DAC should be set to give the desired output voltage for "zero" output from the sensor. The zero DACs output voltage in this case is

    VzeroDAC = Voutput / (Gain DAC * Output Amplifier Gain)

    3. The settling time for this device depends on the gain as shown in the spec table: 

    However, these values do not include the delay introduced by the temperature ADC's measurement. Because the temperature ADC returns a value after every 125ms, there may be a delay before the gain and zero DACs are updated in order to give a more accurate value. 

  • 0 in reply to John Caldwell
    TI__Mastermind 27715 points

    Hello Koji,

    I want to add one comment on the accuracy of the PGA309. This device is intended to be calibrated with a 3-point calibration routine, at up to 17 different temperatures. After calibration, the device can achieve error performance of < 0.1%FSR.

    Best regards,

    Ian Williams
    Linear Applications Engineer
    Precision Analog - Op Amps

  • 0 in reply to Ian Williams
    Guru 12155 points

    Hi Ian

    Thank you for your support.

    I explained  your comment to customer.Then it was good for customer. 

    The evaluation have been made continue.

    Can I ask simple question.

      .- What does 0.01% of Vout settling Time  means.

       - How much voltage of FS(Full Scale).

           (Does it depends on output resistor?) 

    Regards,

    Koji 

  • 0 in reply to K.Hamamoto
    TI__Mastermind 27715 points

    Hello Koji,

    VOUT settling time (0.01%) is the time required for the output to settle to within 0.01% of its final value when a step is applied to the input.

     Full-scale voltage is the difference between the maximum output and the minimum output. It does not depend on the output resistor, as the output resistor is inside the feedback loop and is compensated for in calibration. For example, a common output voltage range after calibration is from 0.5V to 4.5V. This is a full-scale range, or span, of 4V. We typically specify the error after calibration as % of the full-scale range. For example, if your ideal output is 4.5V, and your measured output is 4.498V, the Error%FSR is calculated by the following:

    Best regards,

    Ian Williams