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ADS8556: Full scale range and Vref

Takeshi Sasaki
Expert 4480 points
Part Number: ADS8556


Hi team,

Could you give me comment on following customer questions?

Q1. Can ADS8556 be used as 0~4*Vref with 16-bit full scale range, instead of bipolar symmetrical range like -4*Vref~+4*Vref?

For REFDAC[9:0], the customer thinks that it can be used as programming Vref. For that case,

Q2-1. Can it be used with hardware mode (HW/SW = 0)? The customer assumes no.

Q2-2. Can it be used with REF_IO pin as external input? The customer assumes no.

Best regards,

Takeshi Sasaki

  • 0
    TI__Mastermind 46665 points

    Hi Takeshi,

    The answers to your questions:

    1. No, the ADC can only support +/-4Vref or +/-2Vref bipolar range.

    2-1. Yes, however you have to change the Control Register(CR) settings in software, then you can switch it back to the hardware mode. The CR settings are not affected when switching to the hardware mode.

    2-2. I guess you mean REF_IO pin as external "output", yes, however we do not recommend to use it for any external circuit because the internal reference has very limited driving ability and it can be easily damaged.

    Best regards,

    Dale

  • 0 in reply to Dale Li
    TI__Expert 4480 points

    Hi Dale,

    Could you give me comment on additional customer question?

    Q1. For the answer 2-1., the CR settings will be reset in turning power off. If so, the CR setting goes to default after turning power off,  and the customer has to set the CR setting as they want to do in software mode and switch it back to the hardware mode every after turning power on. Is it correct understanding?

    Best regards,

    Takeshi Sasaki

  • 0 in reply to Takeshi Sasaki
    TI__Mastermind 46665 points

    Hi Takeshi,

    Correct. Actually the datasheet has stated it in section 7.4.1 Hardware Mode as below:

    "Generally, the device can be used in hardware mode and switched into software mode to initialize or adjust the control register settings (for example, the internal reference DAC) and switched back to hardware mode thereafter."

    Best regards,

    Dale