• State Resolved
  • Locked Locked
  • Replies 12 replies
  • Answers 1 answer
  • Subscribers 14 subscribers
  • Views 844 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.

ISO7240M: Unexpected glitch during power up

ttd
Mastermind 8600 points
Part Number: ISO7240M
Other Parts Discussed in Thread: ISO7740, , ISO7240CF

Tool/software:

Dear Technical Support Team,

Unexpected momentarily glitch(about 2.5V , 8us) on the output during power up, at a time when Vcc2 is at about 2.5V.

See attached file.

Waveform.pdf

Q1
Do you have any work around to avoid glitch?

Q2
What root cause does this problem?
Since glitche occurs around Vcc2=2.5V, I assume that the output circuit at that time may still be indeterminate and is High.
(Operation is guaranteed at Vcc2=3.16V or higher.)

Q3.

How about ISO7740(OOK) to avoid problem?  ISO7240M is edge-based.

【Conditions】
・ISO7240MDW
・Vcc2 (5V) power up about 2.5ms after Vcc1 (3.3V) power up at first.
・LOW level voltage is already applied to the Input pin.
・Enable pin is connected to the 5V power supply.
・There is no pull-up resistor on Output pin.

Best Regards,

ttd 

  • 0
    TI__Genius 17775 points

    Hello,

    Please give me more time to review this information. I will get back to you on Monday.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Mastermind 8600 points

    Hi Aaditya Vittal,

    Thank you for your reply.

    About Q3, I found similar issue about ISO7740(default High) and ISO7740F(default low) avoids short pulse.

    https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/820936/iso7740-secondary-side-output-outputs-h-level-shortly-when-the-secondary-sode-power-is-powered-up-is-this-no-irregular-operation

    Best Regards,

    ttd

  • 0 in reply to ttd
    Mastermind 8600 points

    Hello,

    Do you have any updates on this issue?

    Best Regards,

    ttd

  • 0 in reply to ttd
    TI__Genius 17775 points

    Hello,

    Thank you for your patience and sorry for the delay.

    ttd said:
    About Q3, I found similar issue about ISO7740(default High) and ISO7740F(default low) avoids short pulse.

    Yes, this E2E is essentially addresses the same issue as well.

    As mentioned in the similar E2E, the device output channels will initially go to the default state after power-up for a very short time, then it will follow the input signal. 

    ttd said:
    Since glitche occurs around Vcc2=2.5V, I assume that the output circuit at that time may still be indeterminate and is High.
    (Operation is guaranteed at Vcc2=3.16V or higher.)

    Yes you are correct, since the VCC2 is not fully powered up, the output on VCC2 side will be at default state for a few micro seconds, as you have measured. 

    In order to fix this, choosing a isolator with same default state as the input signal may help avoiding small pulse. Since the input signal is LOW, the digital isolator with LOW as default state will work.

    ttd said:
    How about ISO7740(OOK) to avoid problem? 

    Yes, this could be an option for the customer. Considering my comment above, the ISO7740F has a default LOW state and may be a good option for the customer.

    If customer input is LOW after power-up and customer doesn't want to see such a small pulse then customer can use a default LOW device ISO7740F. This will make sure output first goes to LOW and then starts to follow the input. Since default state and input state after power-up are the same, customer will not see any pulse at the output. Similarly, if the input is HIGH after power-up, customer can use default HIGH device ISO7740 (without 'F' suffix) so that the output doesn't see any pulse.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Mastermind 8600 points

    Hi Aaditya Vittal,

    Thank you for your answer.

    I got the workaround to avoid the current issue with ISO7740F(default Low).

    I have other question about ISO7240.

     Aaditya Vittal said:

    In order to fix this, choosing a isolator with same default state as the input signal may help avoiding small pulse. Since the input signal is LOW, the digital isolator with LOW as default state will work.

    Is it workaround with ISO7240CF(CTRL = L (Default output Low))?

     Aaditya Vittal said:

    Similarly, if the input is HIGH after power-up, customer can use default HIGH device ISO7740 (without 'F' suffix) so that the output doesn't see any pulse.

    Is this effective workaround with ISO7240MDW(Default High)?

    ISO7240CF(Default output Low with CTRL pin) is not pin compatible with ISO7240MDW.

    ■Steps 

    1. VCC1=0V, VCC2=0V VIN=Low
    2. VIN=High after VCC1=3.3V powerup,  VCC2=0V 
    3. VCC1=3.3V, VIN=High, VCC2=5V powerup finally ⇒ Can I prevent glitch since we input the same "High" as Default output "High"?


    Best Regards,

    ttd

  • 0 in reply to ttd
    TI__Genius 17775 points

    Hello,

    Please give me additional time to review. I will respond within 24 hours.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Mastermind 8600 points

    Hi Aaditya Vittal,

    Thank you for your investigation.

    Please give priority to following question.

    Is this effective workaround with ISO7240MDW(Default High)?

    Best Regards,

    ttd

  • 0 in reply to Aaditya V.
    Mastermind 8600 points

    Hi,

    Here is additional information about "Can a digital signal be applied to digital isolator input when its respective VCC is 0V?"

    https://e2e.ti.com/support/isolation-group/isolation/f/isolation-forum/1361889/faq-can-a-digital-signal-be-applied-to-digital-isolator-input-when-its-respective-vcc-is-0v

  • +1 in reply to ttd
    TI__Genius 17775 points

    Hello,

    Thank you for your patience and you questions.

    ttd said:
    Is it workaround with ISO7240CF(CTRL = L (Default output Low))?

    This may be an option. However, there are a few things that you have to consider:

    • The data rate of the ISO7240CF is much lower than the ISO7240M
    • As mentioned, the pinout is also slightly different (NC and EN instead of the CTRL and DISABLE pins)

    From the highlighted portion of the table, you can see that the Output = LOW when VCC1 is powered down and CTRL = LOW.

    ttd said:

    Is this effective workaround with ISO7240MDW(Default High)?

    ISO7240CF(Default output Low with CTRL pin) is not pin compatible with ISO7240MDW.

    This was mainly an example statement to show that the default state of device should match the input signal state during power up. 

    Considering these things, we would still recommend the ISO7740F device, since it is default LOW output and also high data rate device. the ISO7740F is also our newest and most popular high data rate device: ISO7740 data sheet, product information and support | TI.com

    ttd said:
    Here is additional information about "Can a digital signal be applied to digital isolator input when its respective VCC is 0V?"

    This FAQ discusses if a signal can be applied when the respective VCCx is 0V. For example, if a 5V signal is applied on INx on VCC1 side, but the VCC1 is 0V, the absolute maximum ratings would be violated and can cause damage to the device. for more detail, Please visit the FAQ you have linked above.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    Mastermind 8600 points

    Hi Aaditya Vittal,

    Thank you for your reply.

    I'd like to confirm ISO7740F spec.

    How about following step with ISO7240MDW(Default High)?

    According to FAQ and your answer, VCC1=0 doesn't accept VIN=High.

    So VCC1 power up first and next VIN=High is possible like following steps?

    ---------------------------------------------------------- 

    Aaditya Vittal said:

    Similarly, if the input is HIGH after power-up, customer can use default HIGH device ISO7740 (without 'F' suffix) so that the output doesn't see any pulse.

    Is this effective workaround with ISO7240MDW(Default High)?

    ■Steps 

    1. VCC1=0V, VCC2=0V VIN=Low
    2. VIN=High after VCC1=3.3V powerup,  VCC2=0V 
    3. VCC1=3.3V, VIN=High, VCC2=5V powerup finally ⇒ Can I prevent glitch since we input the same "High" as Default output "High"?

    ---------------------------------------------------------- 


    Best Regards,

  • 0 in reply to ttd
    TI__Genius 17775 points

    Hello,

    Thank you for your response.

    Please give me additional time to review.

    Regards,
    Aaditya Vittal

  • +1 in reply to Aaditya V.
    TI__Genius 17775 points

    Hello,

    Thank you for your questions and for your patience.

    ttd said:
    According to FAQ and your answer, VCC1=0 doesn't accept VIN=High.

    Yes, when VCC is powered down, we recommend no input signal as the absolute maximum ratings would be violated.

    ttd said:
    VCC1=0V, VCC2=0V VIN=Low
    2. VIN=High after VCC1=3.3V powerup,  VCC2=0V 
    3. VCC1=3.3V, VIN=High, VCC2=5V powerup finally ⇒ Can I prevent glitch since we input the same "High" as Default output "High"?
    ttd said:
    Can I prevent glitch since we input the same "High" as Default output "High"?

    Yes, I believe these steps should be fine. Since the default output is HIGH and the input would be HIGH when device is powered up, this should be fine.

    Regards,
    Aaditya Vittal