• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 14 subscribers
  • Views 694 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.

ISO1228: Clarifications needed on preliminary datasheet

Matt Calvo
Genius 14755 points
Part Number: ISO1228

Hey Isolation team,

I have a customer evaluating the ISO1228 for a new project and there are a couple of items in the datasheet that we were hoping to get more clarity from you on:

  • In Section 9.2.3.1.2 Voltage Thresholds, it mentions that for Type 2 operation it is recommended to use two channels in parallel. Does this mean that there is a limit in current through the individual inputs? Is it correct to interpret this as the device cannot support 8 inputs in Type 2 mode?
  • Again in Section 9.2.3.1.2 Voltage Thresholds, it states that a R_THR value of 1.35kOhm is recommended in Type 3 systems for I_L of 3.5mA in sink mode but then Table 9-1 shows that the TYP and MAX R_THR values for this exact situation are 910Ohm and 950Ohm respectively. Is this discrepancy a typo? Which one is correct? 

Any guidance you can provide here would be greatly appreciated!

Best regards,

Matt Calvo

  • 0
    TI__Expert 8030 points

    Hi Matt,

    Thanks for reaching out.

    Matt Calvo said:
    In Section 9.2.3.1.2 Voltage Thresholds, it mentions that for Type 2 operation it is recommended to use two channels in parallel. Does this mean that there is a limit in current through the individual inputs? Is it correct to interpret this as the device cannot support 8 inputs in Type 2 mode?

    For this device, the current limit for all of the input channels can either be set at 2.5 mA or 3.5 mA. In order to achieve the recommended current limit of 7 mA for Type 2 inputs, two of the input channels will have to be connected in parallel whenever the device current limit is set to 3.5 mA. Therefore, the device is not able able to support 8 Type 2 digital inputs. 

    Matt Calvo said:
    Again in Section 9.2.3.1.2 Voltage Thresholds, it states that a R_THR value of 1.35kOhm is recommended in Type 3 systems for I_L of 3.5mA in sink mode but then Table 9-1 shows that the TYP and MAX R_THR values for this exact situation are 910Ohm and 950Ohm respectively. Is this discrepancy a typo? Which one is correct? 

    I'm currently in the process of reaching out to other members of the team to try and understand why the datasheet is written in this way. I will provide you with an update on this later this week.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    TI__Genius 14755 points

    Thanks for the explanation Kenneth! For the first part, I'll go ahead and relay that info to my customer and have them comment back on this thread with any follow-up questions they may have.

    For the second part, thanks for digging into this further. Please let us know what you find out in terms of a potential typo or discrepancy on the preliminary datasheet.

    Best regards,

    Matt

  • 0 in reply to Matt Calvo
    TI__Expert 8030 points

    Hi Matt,

    Thanks for the update. I recently received clarification about this datasheet error from another team member. I will provide a follow up response clarifying this later today.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    TI__Expert 8030 points

    Hi Matt,

    Thank you for your patience. 

    Your assumption is correct, the portion of the datasheet that your initial question addressed does contain incorrect information.

    The recommendation is to have RTHR equal to 1.35 kΩ in Type 3 Systems that are using the device in source mode at IL = 2.5 mA. For Type 3 Systems that are using the device in sink mode, RTHR should be equal to 910 Ω when IL= 3.5 mA and 1 kΩ when IL = 2.5 mA.

    If you have any further questions, please let me know.

    Regards,

    Kenneth

  • 0 in reply to Kenneth Arnold
    TI__Genius 14755 points

    Hey Kenneth,

    Thanks for following up on this! I assume that this will get corrected in the datasheet for the next release but in the meantime can you please help to confirm the following conclusions based on your reply:

    • There are no errors in Table 9-1 and Table 9-2 in the current version of the datasheet and the information presented is correct as-is
    • The following excerpt in the datasheet today is incorrect:
      • A value of 1 kΩ is recommended for RTHR in Type 3 systems for IL of 2.5 mA and 1.35 kΩ for IL of 3.5 mA in sink mode
        (maximum threshold voltage required is 11 V).
      • The correct sentence should read: A value of 1 kΩ is recommended for RTHR in Type 3 systems for IL of 2.5 mA and 910 Ω for IL of 3.5 mA in sink mode (maximum threshold voltage required is 11 V).

    Are all of the above conclusions correct in terms of today's version of the datasheet? 

    -Matt

  • +1 in reply to Matt Calvo
    TI__Expert 8030 points

    Hi Matt,

    Thanks for the update.

    Matt Calvo said:
    There are no errors in Table 9-1 and Table 9-2 in the current version of the datasheet and the information presented is correct as-is

    Yes, the information in the table is correct, and should be used by the customer when determining the value of RTHR that is recommended for their application.

    Matt Calvo said:
    The correct sentence should read: A value of 1 kΩ is recommended for RTHR in Type 3 systems for IL of 2.5 mA and 910 Ω for IL of 3.5 mA in sink mode (maximum threshold voltage required is 11 V).

    Yes, the sentence that you have written is correct.

    Regards,

    Kenneth