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ADuM3160 speed config

I have an application using the ADuM3160 where the customer wants to be able to dynamically select between lo-speed and full-speed mode.  The datasheet says that the part cannot make this adjustment on the fly so I added provision to cycle power on both sides of the isolator.

Are there any power sequencing requirements for Vbus1 and Vbus2?

What are the timing requirements for the SPD/SPU pins being set with respect to their power rails coming up?



  • Hi Matt,

    The SPU and SPD are level sensitive inputs, they can be changed after power up and the effect is immediate.  It changes the properties of the I/O buffer and the logic for detecting an idle J.  However implementing an on the fly change can be tricky as far as the USB controllers on the line are concerned.  Once the line has been enumerated, the controller will get confused if the line starts to behave like another speed without the cable being disconnected.

    Cycling power should not be required, however, a disconnected cable is required so that the line will be forced to enumerate again.  This can be accomplished by pulling the PIN line low, that will disconnect the pullup on the upstream side and the controller will think a cable has been unplugged.  So what I would recommend is not messing with power, but pull PIN low, prior to changing SPU and SPD then pulling PIN high to allow application of the pullup.  This should make a clean transition, even if the cable is not physically unplugged.

    The only pin that is samples at power up is the PDEN pin.  That should only be changed before power is applied, but you should not ever need to use that pin.

    I hope this helps.