ADuM4120 continuous output curren

Hi,

ADuM4120 datasheet secifies peak current but I would like to know maximum continuative source and sink current (no switching) of the device at maximum suggested VDD2.

The application isn't related to a mosfet driver.

Many thanks

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  • +1
    •  Analog Employees 
    on Jan 25, 2021 8:39 PM

    Hello,

    Unfortunately, the ADuM4120 can't source or sink very much DC current.

    The ADuM4120 was designed for short durations of output current. If a constant current is pulled through the internal FETs, there is a lot of self heating that will occur. This self heating is the main limitation on the DC current output. As an estimate, we can use the power dissipation within the part to be the internal FET resistance times the square of the current being sourced or sunk. Let's limit the package temperature increase to 50ºC, which is very high. Looking at the Theta-Ja of 123.7 ºC/W, we find we can put around:

    50ºC / 123.7ºC/W = 0.4 W

    0.4 W before we reach the limit of 50ºC self heating. Solving for I with the worst case Rdson:

    Pdiss = I^2 * Rdson

    I = sqrt(Pdiss / Rdson) = sqrt(0.4 W / 1.8Ω) = 0.85 A

    This assumes you can control the source/sink current somehow, either with external resistance, or some other means. 50ºC is an aggressive target, and self heating should probably be limited much more than that.

    If you are looking to have a compact, isolated switch that can support higher currents, you might be able to use an external MOSFET and the ADuM5230. This would allow you to power the secondary side from the ADuM5230 itself, and by using an external MOSFET, you can safely drive the DC currents.

    RSchnell

Reply
  • +1
    •  Analog Employees 
    on Jan 25, 2021 8:39 PM

    Hello,

    Unfortunately, the ADuM4120 can't source or sink very much DC current.

    The ADuM4120 was designed for short durations of output current. If a constant current is pulled through the internal FETs, there is a lot of self heating that will occur. This self heating is the main limitation on the DC current output. As an estimate, we can use the power dissipation within the part to be the internal FET resistance times the square of the current being sourced or sunk. Let's limit the package temperature increase to 50ºC, which is very high. Looking at the Theta-Ja of 123.7 ºC/W, we find we can put around:

    50ºC / 123.7ºC/W = 0.4 W

    0.4 W before we reach the limit of 50ºC self heating. Solving for I with the worst case Rdson:

    Pdiss = I^2 * Rdson

    I = sqrt(Pdiss / Rdson) = sqrt(0.4 W / 1.8Ω) = 0.85 A

    This assumes you can control the source/sink current somehow, either with external resistance, or some other means. 50ºC is an aggressive target, and self heating should probably be limited much more than that.

    If you are looking to have a compact, isolated switch that can support higher currents, you might be able to use an external MOSFET and the ADuM5230. This would allow you to power the secondary side from the ADuM5230 itself, and by using an external MOSFET, you can safely drive the DC currents.

    RSchnell

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