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ADS8688A: REFIO as input

Renan Santos Adriano
Mastermind 22260 points
Part Number: ADS8688A

Hello Team,

My customer would like to know if it is possible for the pin REFIO to have 2.5v as external reference input or not?

SECTION 8.3.8.2 first paragraph (datasheet) an external 4.096-V reference must be applied at REFIO (pin 5), which becomes an input pin.

Then he is pointing out the next statement that: 

"Any low-power, low-drift, or small-size external reference can be used in this mode because the internal buffer is optimally designed to handle the dynamic loading on the REFCAP pin, which is internally connected to the ADC reference input."

Regards,

Renan

  • 0
    TI__Mastermind 45455 points

    Hi Renan,

    Firstly, this ADC supports external voltage reference, for sure. Secondly, the recommended external reference voltage is 4.096V, see the requirement below. 

    Also, the ADS8688A can support many bipolar and unipolar input ranges on each input as below:

    – ±10.24 V, ±5.12 V, ±2.56 V, ±1.28 V, ±0.64 V

    – 10.24 V, 5.12 V, 2.56 V, 1.28 V

    Is there any specific reason the customer wanted to use external 2.5V reference voltage?

    Best regards,

    Dale

  • 0 in reply to Dale Li
    TI__Mastermind 22260 points

    Hello Dale,

    Thank you for this response. They want to configure the ADC for the input range as +/- 6.25V or 0 to 6.25V. So they have given 2.5V reference as external ref IO. Will it work now or not? Or what should they do to have the mentioned input range? 

    Regards,

    Renan

  • 0 in reply to Renan Santos Adriano
    TI__Mastermind 45455 points

    Hi Renan,

    The scale ratio is 2.5 for 4.094V reference voltage and +/-10.24V range. When a 2.5V reference is used, +/-6.25V range should be able to get if the same scale is selected, however the performance specified in the datasheet may not be achieved because all specifications in the datasheet were characterized with a 4.096V reference voltage and this is the reference voltage recommended in the datasheet. I never tested this ADC with a 2.5V reference, the customer can try and check the performance by themselves but we can not guarantee.

    Best regards,

    Dale