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ISOM8110: What is the storage time parameter?

Adam Torma
Mastermind 45475 points
Part Number: ISOM8110

Tool/software:

e2e, 

Could you comment on the storage time (ts) parameter. There is no comment on what it is other than Figure 7-3 showing that it is part of toff. Section 6.8 shows a maximum of 21us which is much slower than the worst-case toff of 14.5us. 

 

When I look at Figure 6-29, I see a ts of about 6.1us.  That graph is for Rl-4.7K, If = 1.6mA and Vcc = 5V which is the same setup for the ts spec of 21us.

I previously was told the spec was characterized at room temperature according to the datasheet. For variance overtemperature you can use Figure 7-11. Switching Time vs Ambient Temperature to find the results specific to your use case. Part to part variances on timing spec is +/- 20%, but most devices will be around the typical value.”  But 21us is a lot more than +20% of any toff times listed for this part. 

Just trying to understand what I’m missing.

Adam

  • 0
    TI__Mastermind 22525 points

    Hi Adam, 

    Thank you for reaching out. TOFF should be equal to Ts + Tr, and this relationship is unclear due to the spec ts only listing a maximum and TOFF only listing a typical value. I suspect that this issue related to Tr being taken at a different loading condition than TOFF and Ts. 

    I will review this with our systems team after the holiday.

    Best,
    Andrew

  • 0
    Guru 286090 points

    The ISOM811x has a BJT at the output, and the specified storage time is the storage time of that BJT. And storage times indeed can have a large variance.

    The storage time is always shorter than the turn-off time. The datasheet shows only typical turn-off times. The rise time will not have large manufacturing variations (but depends on the R-C load), so for a specific load, you can estimate the maximum turn-off time by adding the rise time to the maximum storage time.

  • 0 in reply to Clemens Ladisch
    TI__Genius 12245 points

    Hello,

    Thank you for reaching out.

    Please allow us until Monday next week (12/2/2024) to reply as we have a US Holiday.

    Regards,
    Aaditya Vittal

  • 0 in reply to Aaditya V.
    TI__Mastermind 22525 points

    After review, 

    The method Clemens described is the best. "You can estimate the maximum turn-off time by adding the rise time to the maximum storage time." This will be close to the worst-case value. 

    Best,
    Andrew