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UCC5320: what's the maximum switching frequency

Howard Zou
Genius 12365 points
Part Number: UCC5320

Hi,

my question is not specifically for UCC5320 but for all gate driver.

Our datasheet does not tell what switching frequency the gate driver can achieve, but sometimes the customer will ask such question, so how to answer?

Can we say that cap isolated gate driver maximum switching frequency is inherently higher than opto isolated gate driver? If yes, why?

Another question is the IC's behavior when broken down.

The customer says that for magnetic or opto isolated gate driver which breaks down, the primary side and secondary side are open circuit. But for cap isolated gate driver which breaks down, the primary side and secondary side are short circuit. Is it true? If yes, that will be a weak point for cap isolation.

  • 0
    TI__Intellectual 2805 points

    Hello Howard, 

    Instead of determining the maximum frequency of our gate drivers, we recommend our customers to operate our devices below the maximum junction temperature T_J(max).  This application report goes into detail on how to calculate the junction temperature using the thermal metrics from the datasheet: 

    Each device will have different thermal metrics, therefore it is difficult to say that all gate drivers have superior thermal capabilities compared to optocouplers. 

    Our capacitive isolation adheres to safety regulations which require basic isolation to be supplemented with a secondary isolation barrier for redundancy, so that the additional barrier provides shock protection, even if the first barrier fails. Please see the following white paper on this subject: 



    If this answered your question, please press the green button. 

    regards,
    Mateo

  • 0 in reply to Mateo Begue
    TI__Genius 12365 points

    Mateo,

    1. So you mean that we won't guarantee any switching frequency for our gate driver, right?

    2. For failure mode 2: A combination of high voltage and high current close to the isolation barrier.

    Our reinforced isolators can guarantee "fail open". Optocoupler will be "fail short".

    I guess our basic isolator will also be "fail short", right?

    How about magnetic isolator?

    3. For Failure mode 1: High voltage across the isolation barrier.

    No matter it's TI reinforced, TI basic, optocoupler, or magnetic, it's all "fail short", right?

  • 0 in reply to Howard Zou
    TI__Intellectual 2805 points

    1. Correct. We can only guarantee what is in the datasheet. I have personally seen the UCC53x0 family operate above 2-MHz while under the max junction temperature. If customers are operating at switching frequencies above this, then we have to look into the application and see if silicon-based gate drivers are the best option for them. 

    2. Both basic and reinforced capacitively isolated gate drivers have two series capacitors (TX and RX). For basic isolation, it can be assumed that it will have half of its isolation capability left after this failure. 

    Unfortunately, our isolation team did not do this comparison with magnetic isolators. 

    3. Yes. For failure mode 1 all devices fail short. 

    regards,
    Mateo

  • 0 in reply to Mateo Begue
    TI__Genius 12365 points
    Mateo,
    Both basic and reinforced capacitively isolated gate drivers have two series capacitors.
    So both reinforced isolated gate driver and basic isolated gate drivers can guarantee "fail open", since only one cap will be shorted and the other one will still be open. Right?
  • 0 in reply to Howard Zou
    TI__Intellectual 2805 points

    Hello Howard, 

    For failure mode 1: all isolators by definition "fail short" when voltages across the isolation barrier exceed rated limits. 

    For failure mode 2: Damage in this mode is limited to one capacitor. This leaves the other capacitor intact causing these isolators to "fail open". Approximately half of the original isolation is preserved in this failure mode. 

    regards,
    Mateo

  • 0 in reply to Mateo Begue
    TI__Genius 12365 points
    Mateo,
    You said "Both basic and reinforced capacitively isolated gate drivers have two series capacitors".
    So I wonder if "fail open" apply to both reinforced isolated gate driver and basic isolated gate driver.
  • 0 in reply to Howard Zou
    TI__Intellectual 2805 points

    Hello Howard, 

    Yes, fail open applies to both.

    Regards,
    Mateo