• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 197 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

ADS7844: Clarification of Absolute Maximum Input Voltage Rating and Default Control Register State

Shane Miller-Tait
Prodigy 70 points
Part Number: ADS7844

Hi,

In the datasheet for the ADS7844, the absolute maximum input voltage rating for the analog inputs is given as -0.3 V to VCC + 0.3 V. However, in the specification table, an "absolute input range" for the negative inputs (when operated in differential mode) is given as -0.2 V to 1.25 V. I believe that "absolute" has been used in this context in order to differentiate from the differential input range rating, and that this should not be interpreted as an absolute maximum rating. (E.g. if a negative input is driven to, say, 1.5 V, the conversion will not be accurate, but no damage will occur.) Is this correct?

Further, the datasheet does not provide default values for the control byte bits (Table III), so it is unclear whether the converter will start up in single ended or differential mode. What is the default value of this register?

Thanks

Shane

  • 0
    TI__Mastermind 24940 points

    Hello,

    Your understanding is correct about the ratings for the pins. Each analog input can sustain a voltage up to VCC, but when in differential mode, the voltage at IN- should be within -0.2V to 1.25V, for bet performance. Outside of this, as you noted, the device will not be damaged but will not perform as expected. 

    The start up logic of the SGL/DIF does not matter, as the control byte needs to be set before a conversion takes place. the device will not start a conversion without the control byte, thus the default logic of this register is never actuated. 

    Regards

    Cynthia

  • 0 in reply to Cynthia
    Prodigy 70 points

    Thanks for the prompt and clear answer Cynthia.