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Review Schematic for ADUM4160 and ADUM5000

Category: Hardware
Product Number: ADUM4160 & ADUM5000

Built a prototype of a USB isolater circuit but I am having issues with it, I am getting all required voltages on either side of the transformer, but the USB device does not appear in USB View. Please review my schematic and give feedback of possible issues. 

VBUS 1 4.90V
VDD 1 3.20V
VBUS 2 4.90V
VDD 2 3.19V

  • I can review this a bit more if needed, including maybe layout, but so far I can spot two possible issues.

    1. The USB device connected downstream on J1 may require more power than ADuM5000 can offer; the power required by ADuM4160 must be subtracted from the output, resulting in up to 92 mA available on downstream 5V compared to a peripheral maybe expecting 500-900 mA.
    2. The USB Type C connector P1 only has two connector pins connected to D+, D- rather than the second pair of pins, meaning that it might only work in one orientation, you might need to try connecting both ways up.

    Best regards,

    Conal

  • 1. I have nothing connected to the downstream port, it is not appearing in my USB view software even though there is voltage on the downstream port. I did not take into consideration of the power limitations, would you have suggestions for a more capable power supply?

    2. I know for sure the USB-C connector works as I have made other designs with USB 2.0 like this. The device is only one way.

  • ADuM4160 UD+, UD- will mirror the DD+, DD- state, including pull-up on UD+ or UD- (with SPD, SPU tied low, the pull-up will be on UD-, when a low speed peripheral is connected to DD+, DD- with corresponding pull-up on DD-).

    So I expect that the USB view software will not show any change with just the circuit above connected, as the isolator will present a "disconnected" state on the physical layer (host should behave as if its port is not physically connected to a USB peripheral).

    LT3999 is a common choice for isolated DC-DC design alongside the USB isolators. Alternatively LTM2884 is a complete integrated solution including both USB isolator (auto low/full speed) and 2.5W isolated DC-DC.

  • Just ran another test with a USB flash device plugged into the receptacle (tested previously and does not draw more than 90mA) and I get an enumeration issue, I can't figure out the root cause of this. Do you have any thoughts on this?

  • I think the USB flash device should try low speed (pull-up on D-) after full speed doesn't work (pull-up on D+, ADuM4160 is set up in your circuit to monitor for D-/low speed, with SPU and SPD low). However, you could try a real low speed device, maybe a mouse or keyboard, and see if that enumerates OK.

    A USB 2.0 flash drive will probably be intended for high speed operation, but high speed is always initiated by starting in full speed (and the device remains in full speed if the host doesn't participate in the high speed handshake). So SPD + SPU high might suit the default starting state of a USB 2.0 flash drive.

    Otherwise, there could be some sequencing issue (it's not clear why there would be, but another thing to consider). Have you tried connecting onto J1 first, then powering by connecting P1, vs. connecting P1 with J1 empty (power just the isolator circuit) and then connect onto J1?

    Is P1 an integrated Type C plug rather than a receptacle for a cable? Using a Type C connector is the main thing I'm not as familiar with in this schematic, but my understanding is that once you have 5.1k on CC, the USB 2.0 functionality remains as before (pull-up on data line is used to detect device/speed). If P1 is a receptacle, should it have 5.1k on both CC pins?

  • I just retried with a standard mouse, works fine, tested both methods (plugging in J1 before P1 and P1 then J1) In order for a USB flash drive to work what changes would you suggest? It is indeed a plug, your understanding was correct with one 5.1k resistor for USB 2.0 plug operation and dual 5.1k for receptacle use.

  • Although you mention the USB flash drive "does not draw more than 90mA", I would attempt to monitor the USB 5V downstream (output of ADuM5000) and check for the voltage dipping. The LED on the board will further reduce the available current, actually probably just below 90 mA.

  • I never actually placed the LED or accompanying resistor, was just there as an extra footprint, I've checked, and as long as I have about 100mA available current it is fine for the required application.