• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 428 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.

UCC21520: What's the modulation scheme?

Howard Zou
Genius 12365 points
Part Number: UCC21520
Other Parts Discussed in Thread: ISO7721, , UCC5320, UCC23513

Hi,

in our digital isolator like ISO7721, we specify the modulation scheme to be OOK.

How about our isolated gate driver?

And UCC21520 specify "10-ns Minimum Pulse Width" in datasheet page 1.

Does this mean that any iput pulse width shorter than 10ns will not affect the output state?

In datasheet page 10, section 6.10. We also said the maximum minimum pulse width to be 20ns, so 10ns is the typical value?

My customer has ever used some other gate driver which also specify the parameter "Minimum Pulse Width", and if the pulse width is less than "Minimum Pulse Width", the output will be constantly on, which is not what they wanted and is caused by the modulation scheme. That's why I ask the modulation scheme of our isolated gate driver. And not all of our isolated gate driver has such parameters.

  • 0
    TI__Expert 3355 points

    Hi Howard,

    Thank you for your question. I work on the applications team in the high power drivers group.

    All of our isolated drivers use on-off-keying (OOK) to transmit digital information over the isolation barrier.

    You are correct; 10ns is the typical minimum pulse-width value, 20ns is the max minimum pulse-width value. Anything below the minimum pulse-width value will not affect the output state. If there is an input pulse-width less than the minimum pulse-width value, the output will remain off. There should not be any risk of the output turning constantly on, due to minimum pulse-width.

    If this answered your question, could you please press the green button? If not, please feel free to ask more questions.

    Thanks and best regards,

    John

  • 0 in reply to John Geiger
    TI__Genius 12365 points

    John,

    thank you.

    So why our other isolated gate driver like UCC23513, UCC5320 don't have such parameter?

    Does it mean that no matter how short the input pulse is, it will reflect on the output?

    And some vendor will use OSK for modulation, what's the pros and cons for these two modulation scheme for isolated gate driver?

  • 0 in reply to Howard Zou
    TI__Expert 3355 points

    Hi Howard,

    UCC21520 has this spec because it is commonly used in a wide variety of systems which require these very small pulse widths. UCC23513 and UCC5320 are typically targeted at MOSFET and IGBT power applications for which most designers are not interested in this spec. However, both of these drivers will exhibit some form of minimum pulse-width capability, based on the input filter, which is there to improve noise immunity and CMTI. Our own testing, for example, shows UCC23513 has a typical minimum pulse-width of ~23ns at 27C. This will vary over process and temperature, though.

    Can you please share where you found information on this OSK (output shift keying?) modulation? From what I have seen, other solutions use OOK for their isolation technology, whether using capacitive or coreless transformer technology.

    If this answered your question, could you please press the green button? If not, please feel free to ask more questions.

    Thanks and best regards,

    John