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ISO7740: Want to understand output current source capability

Nilesh Karale
Prodigy 120 points
Part Number: ISO7740
Other Parts Discussed in Thread: UCC27517

Tool/software:

Hello,

I wanted to know current source capability of individual channel of digital isolator part ISO7740. Below plot is from ISO7740 datasheet, is this plot is for individual output channel? Also this isolator can source 15mA with output voltage of 4.1V, is this understanding correct?

I wanted to drive logic level FET using this isolator. Do you see any challenge to drive logic level FET using this?

  • 0
    Guru 316240 points

    The absolute maximum rating for the output current is 15 mA. A capacitive load initially acts like a short, so if the gate capacitance is larger than about 70 pF, then you must add a current-limiting series resistor of at least 5 V / 15 mA = 333 Ω.

    For a really large MOSFET (with a gate capacitance measured in nF) that you need to switch quickly, consider a gate driver like the UCC27517 (in which case you do no longer need a logic-level MOSFET).

  • 0
    TI__Genius 17255 points

    Hi Nilesh, 

    In addition to Clemens statement, I would like to point out that the 15mA specification is an absolute maximum output current. Under normal operating conditions (recommended conditions), the output current is much less. The damage might not be immediate to the device when operating, but repeated electronic overstress can affect the long-term performance and reliability issues. Therefore, we recommend operating under the recommended operating conditions.

    As Clemens stated, using a isolation gate driver will allow you drive a logic level FET.

    Regards,
    Aaditya V

  • 0 in reply to Aaditya V.
    Prodigy 120 points

    Thank you Aditya for your reply.

    My application is like switch either ON or OFF for longer time. Is there any damage happen if I operate with peak current of 10mA for 500nsec?

    Regards,

    Nilesh Karale

  • 0 in reply to Nilesh Karale
    Guru 316240 points

    For any current lower than 15 mA, there will be no damage.

  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    Thank you Clemens.

    Regards,

    Nilesh Karale