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ADS8555EVM-PDK: Is it possible to use ADS8555EVM to evaluate ADS8556 after replace ADS8555 on EVM with ADS8556?

Kazuya Nakai59
Guru 20640 points
Part Number: ADS8555EVM-PDK
Other Parts Discussed in Thread: ADS8556, , ADS8555

Hello guys,

One of my customers want to check ADS8556 performance.
But ADS8556 EVM has not been released.
So they are considering buying ADS8555EVM-PDK for ADS8556 evaluation.
At this moment, they have the following question.
Could you please give me your reply?

Q. Is it possible to use ADS8555EVM to evaluate ADS8556 after replace ADS8555 on EVM with ADS8556?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 38195 points

    Hi Kazuya,

    Yes, the ADS8555EVM board can be used to evaluate ADS8556 ADC. The only difference between the ADS8555 and ADS8556 is the partial power-down mode that is available on the ADS8556; otherwise, essentially the ADS8555 and ADS8556 are the same identical devices. Both of them offer data rates up to 630kSPS in parallel mode or 450kSPS in Serial mode. 

    Regards,

    Dale

  • 0 in reply to Dale Li
    Guru 20640 points

    Hi Dale,

    Thank you very much for your reply.
    I understood that ADS8555 and ADS8556 are the same identical devices except the partial power-down mode.
    Could I ask you a few additional questions as the follows?

    Q1.
    They want to check ADS8556 conversion accuracy using the EVM. They think the device conversion accuracy is less than +/-2.5LSB.
    Is their thought correct?
    Also they would like to confirm whether this accuracy can be achieved really with the EVM. Is this possible?

    Q2.
    If Q1 answers are Yes both, Is there anything they should be careful about for the accuracy checking?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 38195 points

    Hi Kazuya,

    If the customer's input range is +/-10V, +/-2.5LSB is equivalent to 0.0038% or +/-762.9uV, this requirement is very challenging for this device, for example, the offset error of this ADC is +/-4mV maximum and the gain error is +/-0.75% etc., the offset and gain error can certainly be calibrated out, but the errors over temperature should be considered and they are also very challenging. In addition to these, this ADC is a switched-capacitor input ADC, the front-end circuit including amplifier and component selection should be carefully considered, the pcb layout design is also important. I do not have the details about the customer's requirement, however they can check on the EVM.

    Regards,

    Dale

  • 0 in reply to Dale Li
    Guru 20640 points

    Hi Dale,

    Thank you very much for your reply and I'm sorry to be late my response.

    I heard about their calibration way from the customer.
    They implement high accuracy voltage reference for ADC input calibration on their own board.
    Before just ADC measuring starting, they connect the voltage reference to analog signal input of their board instead actual analog signal using analog switch and calibrate offset error and gain error using the voltage reference.

    They have a few additional questions as the follows.
    Could you give me your reply?

    Q1.
    They use 3.0V external reference not ADS8556 internal reference.
    Does this ADC conversion accuracy become better when the external reference is changed to 2.5V? (Of course, input signal voltage range is changed 0~2.5V.) 
    In other word, is this ADC conversion accuracy affected according to the external reference voltage?

    Q2.
    This question may be similar question to Q1.
    Is there any combination pattern of external reference voltage and input voltage range for better accuracy?
    For example, it is better for higher conversion accuracy that same voltage between reference voltage and the maximum input voltage and so on.

     
    Q3.
    Do you have any recommend newer and cost effective device which have similar performance and function to ADS8556?

    Thank you again and best regards,
    Kazuya. 

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 38195 points

    Hi Kazuya,

    The voltage reference's output voltage accuracy, temp drift and noise definitely can affect your conversion accuracy, however the amplitude of reference voltage does not improve your accuracy, actually for low resolution (16-bit) ADCs where quantization noise dominates, you can use a smaller reference voltage to reduce the quantization noise amplitude. When we talk about the "accuracy", we should care about the errors and the source of the errors in the system. For example, you may have a settling error if the ADS8556 is not properly derived because this is a switched-capacitor input structure ADC. Also, you may have to pay attention to the design of your power supply circuit and pcb layout.

    ADS8586S is a 16-Bit 200ksps 6-Channel simultaneous-sampling ADC with bipolar inputs on a single supply. ADS8588S can be considered if an ADC with 8- input channels is expected, ADS8598S is 18-bit version. ADS8588H and ADS8598H can support 500ksps sampling rate.

    Regards,

    Dale