• State Resolved
  • Locked Locked
  • Replies 7 replies
  • Subscribers 46 subscribers
  • Views 537 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PGA with ADS1258

Juliano Felix de Abreu
Prodigy 130 points
Other Parts Discussed in Thread: ADS1258, PGA280

Hello,

 

I need to use the ADS1258 because it has 16 input multiplexed and the output this mux I can put a PGA (Programmable Gain Amplifier).

Firstly, I thought use the PGA280 but your power supply is +/-15V and the ADC1258 is +/-2.5V.

Anyone have a solution for me, a PGA that can be used with the ADS1258, in other words, your power supply is +/-2.5V?

 

Thanks

Juliano

  • 0
    TI__Mastermind 43915 points

    Hi Juliano,

    Do you plan to put this PGA between the MUXout and ADCin pins or before the MUX inputs of the ADS1258? The mux input pins cannot exceed voltages that are larger than what is specified in the data sheet or else you will turn on the ESD diodes.

    The ADS1258 is an unbuffered delta sigma converter so you are going to want to put something between MUXout and ADCin with significant drive strength (1MHz +) to drive the modulator properly.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Hi Tony,

    Thanks for you answer!

    You are right, my plan is put the PGA between the MUX and ADC, because I intend to use all internal multiplex of the ADS1258.

    My question is exactly this, as the PGA that I was intending to use (PGA280) is higher than the threshold voltage of the ADC input, this way I need other PGA that support this voltage. Do you have some suggestion for me, a PGA that I can use between MUX and ADC for the ADS1258? I intend to use the ADS1258 in 128KSPS.

     

    Best Regards

    Juliano

  • 0 in reply to Juliano Felix de Abreu
    TI__Mastermind 43915 points

    Hi Juliano,

    The ADS1258 is an oversampling converter, meaning that it will switch and sample at a rate much faster than the 128kSPS data rate. You will need a driver with enough speed capable of driving the sampling capacitor at the front end of the ADC. The rate at which the modulator samples is call the modulator rate, which is a function of the master clock. I believe in this part, the modulator rate is on the order of a few MHz, meaning that you will need a drive amplifier capable of driving a few MHz in order to properly drive the converter.

    Regards,

    Tony Calabria

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Hi Tony,

    Thanks for your explanation about the frequency of PGA. We estimate that this frequency is higher 1MHz.

    Do you know if the TI has a PGA with a frequency upper 1MHz and that can work with ADS1258 (+/- 2,5 or 0/5Volts)?

    I am asking it because I need work with ADS1258 and the circuit need have a PGA.

     

    Regards,

    Juliano

  • 0 in reply to Juliano Felix de Abreu
    TI__Mastermind 43915 points

    Hi Juliano,

    What type of gain range are you looking for?

    -Tony

  • 0 in reply to Tony Calabria
    Prodigy 130 points

    Hi Tony,

    I am looking for a gain equal of PGA280, gain = 1000 between 0,125V/V until 128V/V, or near this value.

     

    Regards,

    Juliano

  • 0 in reply to Juliano Felix de Abreu
    TI__Mastermind 43915 points

    Juliano,

    I would recommend posting in the linear/amplifier forum for a solution. A PGA with 1MHz + bandwidth and gain options up to 1000 may be difficult to come by and I cannot think of one off of the top of my head.

    Regards,

    Tony