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ISO7221M: confirmation for Vih min/max specification?

AnBer
Mastermind 28880 points
Part Number: ISO7221M
Other Parts Discussed in Thread: ISO7721, ISO7720,

Team,

ISO7220/ISO7221 datasheet says:
1) Vih min/max:
  page 1 -> The M-option devices have CMOS VCC/2 input thresholds and do not have the input noise filter and the additional propagation delay.
  Page 8 -> ISO722xM: Vih  0.7*Vcc
Which one is correct?

2) Voh/Vol:
  page 11 -> Can you please confirm that all ISO7720/ISO7721 listed in the datasheet have the same Voh/Vol specification?

Thanks in advance!

A.

  • 0
    TI__Mastermind 49415 points

    Hi AnBer,

    Thanks for reaching out.

    AnBer said:
    ISO7220/ISO7221 datasheet says:
    1) Vih min/max:
      page 1 -> The M-option devices have CMOS VCC/2 input thresholds and do not have the input noise filter and the additional propagation delay.
      Page 8 -> ISO722xM: Vih  0.7*Vcc
    Which one is correct?

    Sorry about the confusion. The two statements on pages 1 and 8 you are referring to mean the same. The actual thresholds for CMOS inputs are going to be around VCC/2 while VIH isn't the input threshold rather it is the minimum voltage that we recommend user to apply at the input to treat it as a valid HIGH input. i.e., we recommend users to apply at least 0.7*VCC at the input to treat it as a valid HIGH input. Most digital devices with same VCC voltage as ISO shouldn't have any problem in giving out 0.7*VCC as HIGH.

    AnBer said:
    2) Voh/Vol:
      page 11 -> Can you please confirm that all ISO7720/ISO7721 listed in the datasheet have the same Voh/Vol specification?

    VOH and VOL are VCC and IOH / IOL dependent and are specified in the datasheet accordingly. These specifications apply to all channels of ISO7720 and ISO7721. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Dear Koteshwar ,
    you said:
    "VIH isn't the input threshold rather it is the minimum voltage we recommend user to apply at the input to treat it as a valid HIGH input. i.e., we recommend users to apply at least 0.3*VCC at the input to treat it as a valid HIGH input"

    Page 8 of datasheet mentions for ISO722xM as recommended Operation Conditions for valid HIGH Input:    VIH min = 0.7*Vcc.
    But this doesn't match to your answer of "0.3*Vcc at the input to treat as valid HIGH". Where can I find your 0.3*Vcc statement for valid HIGH Input in the datasheet ?

    So, if I use 5V for ISO7221M power supply, can I use MCU with 3.3V Output to control ISO722xM Input ? 

  • 0 in reply to Ulf Zimmermann
    TI__Mastermind 49415 points

    Hi Ulf, AnBer,

    Apologies for the typo in my response. I meant to refer to VIH(min) as 0.7*VCC and instead mistyped it as 0.3*VCC. I have also corrected this in my original response so that others reading these posts read the correct value.

    Ulf Zimmermann said:
    So, if I use 5V for ISO7221M power supply, can I use MCU with 3.3V Output to control ISO722xM Input ?

    For the MCU and ISO722xM to interact reliably, they both need to be powered with same voltage levels. When you test MCU with 3.3V and ISO722xM with 5V, you might see some typical samples work fine under lab test conditions because of the thresholds being close to actual voltages applied but such operation is not guaranteed across temperature and across samples.

    Let me know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao