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Isolator for AM335x: USB I/F as peripheral

Kanae
Mastermind 9635 points

Hi all,

My customer is designing a control board using AM335x and
the board connects USB interface as device/peripheral to host PC.
He try to insert an isolator between USB terminals to USB connector pins.

However AM335x_Schematic_Checklist describes as follows.

Typical connections for a USB peripheral:
-USBx_DP and USBx_DM are connected directly to the USB connector
-USBx_VBUS should be connected directly to the VBUS pin on the USB connector

processors.wiki.ti.com/.../AM335x_Schematic_Checklist

Q1: Is this meant that he should not use an isolator?
Q2: If he can use an isolator, Vbus of an isolator can be supplied 3.3V
  　　from PMIC for AM335x; upstream side, or not?

Best regards,
Kanae

  • 0
    TI__Guru**** 393215 points

    Hi Kanae-san,

    Kanae said:
    Q1: Is this meant that he should not use an isolator?

    I have seen customer schematics where isolators are used. What is the device part number they want to use?

    Kanae said:
    Q2: If he can use an isolator, Vbus of an isolator can be supplied 3.3V from PMIC for AM335x; upstream side, or not?

    AM335X pin USBx_VBUS must sense a voltage >= 4.4V range for the USB peripheral to start: see section 16.3.7 in the AM335X TRM Rev. K.

  • 0 in reply to Biser Gatchev-XID
    Mastermind 9635 points
    Hi Biser,

    Thank you for your quick reply.
    My customer uses "ADuM3160".

    I had mistaken my last question; Q2. Please let me correct it as follows.

    Q2:If he can use an isolator, Vbus of an isolator can be supplied 5V
    from USB cable of Host PC; upstream side and connect it to VBUS pin of AM335x, or not?

    Q3:Could you provide any application example design to use an isolator?

    Best regards,
    Kanae
  • 0 in reply to Kanae
    TI__Guru**** 393215 points

    Kanae said:
    Q2:If he can use an isolator, Vbus of an isolator can be supplied 5V from USB cable of Host PC; upstream side and connect it to VBUS pin of AM335x, or not?

    As I see it this isolator has two power supplies. On the connector side you can supply it from USB cable. On the AM335X side you will need to design an additional optoisolator circuit which signals to the USB_VBUS pin that +5V is present on the USB connector. On AM335X side you can supply the ADuM316 from 3.3V, but you will still need 5V supply for USB_VBUS, and I mean a separate on-board 5V supply, not the one that comes from the USB cable.

    Kanae said:
    Q3:Could you provide any application example design to use an isolator? 

    We don't have any such examples.

  • 0 in reply to Biser Gatchev-XID
    Mastermind 9635 points
    Hi Biser,

    Thank you for your kind reply.
    I understand that AM335x USB_VBUS cannot be supplied 5V from USB cable.

    Best regards,
    Kanae