AD817 and AD826 what is the output short circuit current duration?

I could see from the datasheet that the short-circuit current is 90mA but what is the max duration? In the datasheet, it says 'See Derating Curves'. I don't understand what that means. I am driving capacitive loads directly (16 source pins of AD1434 quad switch, around 252pF) with the opamp as a buffer (and input to opamp is a 3.5V single pulse of width 5us, rise and fall time each of 50ns ) and the peak current (in LTspice) reaches around 85mA lasts for around 10-50ns and then settles for a continuous (for the rest of the pulse duration) of around 58mA for load resistance of around 60ohms (+5-10ohms of switch resistance), Is it safe to operate it like this? 

Here is the output of the current and output voltage:



Here is a part of the relevant circuitry (only one AD1434 has been connected (Cds(ON) =72pF), for the rest, I have added the parasitic source capacitance of 12*15 pF, so a total of 252pF). Everything is powered by ±15V.



Also, does the capacitance of 350pF (to model the worst-case parasitics capacitances of switches in series [not shown here] after the series resistance of 60ohm) affect the opamp output? or is ti just the 252pF load that is directly seen by the opamp?

Also, the datasheet only says min 50mA current but what is the max safe continuous current?



spellingv2
[edited by: paulplusx at 3:30 PM (GMT -5) on 12 Feb 2021]
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  • 0
    •  Analog Employees 
    on Feb 15, 2021 10:00 AM

    Hi,

    The Derating Curve refers to "Maximum Power Dissipation vs. Temperature" which is located at page 3 of both data sheets for AD817 and AD826.

    The Output Current for both parts is minimum of 50mA and the Short Circuit current for both parts is typically at 90mA.
    Your Short Circuit current or Output Current has a relation to your Power Dissipation. This power dissipation has a relationship to your junction temperature of which we keep to be lower than Absolute Maximum Rating.


    Here is a helpful article to understand those relationships:
    https://www.analog.com/media/en/technical-documentation/tech-articles/ms-2251.pdf

    From your example, your max current (~85mA) is less than the short circuit current and I would expect that your device would be still able to provide such current. Also, the working current drive is ~58mA which I think will be more sustainable.

    For your last question, I think maximum is the short circuit current which is 90mA.
    Let me confirm this as well to the responsible Apps Engr.

    Thanks and regards.

Reply
  • 0
    •  Analog Employees 
    on Feb 15, 2021 10:00 AM

    Hi,

    The Derating Curve refers to "Maximum Power Dissipation vs. Temperature" which is located at page 3 of both data sheets for AD817 and AD826.

    The Output Current for both parts is minimum of 50mA and the Short Circuit current for both parts is typically at 90mA.
    Your Short Circuit current or Output Current has a relation to your Power Dissipation. This power dissipation has a relationship to your junction temperature of which we keep to be lower than Absolute Maximum Rating.


    Here is a helpful article to understand those relationships:
    https://www.analog.com/media/en/technical-documentation/tech-articles/ms-2251.pdf

    From your example, your max current (~85mA) is less than the short circuit current and I would expect that your device would be still able to provide such current. Also, the working current drive is ~58mA which I think will be more sustainable.

    For your last question, I think maximum is the short circuit current which is 90mA.
    Let me confirm this as well to the responsible Apps Engr.

    Thanks and regards.

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