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AM3352 USB Host Application

Saravanan Karivandan1
Prodigy 165 points

Other Parts Discussed in Thread: AM3352

Hi all,


Good Morning.  We are planning to use USB0 as a Host in AM3352 Sithara processor . So the USB is required to supply a 5V power source to an attached device through its USB0_VBUS ( ZCZ Ball : P15) line. In order to achieve this task, the USB controller requires the use of an external power distribution switch is capable of sourcing 5V power. We decided to use Micrel power distribution switch of type MIC2025-1YM.

The power distribution switch has the following important pins,

Pin No 7 : IN - Supply Voltage(Input) - This will be connected to 5V line

Pin No 2 : /FLG - Flag output - This will be connected to one of the GPIO lines of the processor in order to identify the short circuit condition

Pin No 1 : EN - Enable input ,Active High - USB0_DRVVBUS ( ZCZ Ball : F16) will be connected to this pin.

Pin No 6 & 8 : OUT - Supply (Output) - This pin will be connected to the USB connector. And also wheteher this pin has to be connected to the USB0_VBUS (ZCZ Ball : P15)??? .

See the Notes from AM3352 schematic check list:

Typical connections for a USB host:

  • USBx_DP and USBx_DM are connected directly to the USB connector
  • USBx_CE is typically not used and can be left unconnected
  • USDx_ID should be grounded
  • USBx_DRVVBUS should be connected to the enable of the 5V VBUS power source.
  • USBx_VBUS should be connected to the output of the 5V VBUS power source

In AM3352 EVB scheme the connected USB0_VBUS (ZCZ Ball : P15) pin to the power distribution switch as a signal. Let me know your view in this.

Waiting for your reply.

Regards,

Saravanan.K

  • 0
    TI__Guru 64015 points

    When this port is operating as standard USB host the USB0_VBUS terminal is a high impedance (40 - 100 Kohm) input that monitors the voltage applied to VBUS.  The power distribution switch should be current limited which will cause the voltage to drop when there is an over-current condition.  The USB controller will generate an over-current interrupt if the voltage drops below 4.4 volts.  Connecting the flag output to a GPIO would only provide the application code an alternative way of detecting an over-current condition and may not be necessary if the GPIO is needed for other functions.

    Regards,
    Paul

  • 0 in reply to peaves
    Prodigy 165 points

    Dear Paul,


    Thanks for your response. When this port is operating as standard USB host, 5V will be available on the USB0_VBUS pin. Is it right??? In this case whether this pin has to be connected to OUT pin of power distribution switch(MIC2025).


    See the snapshot of " AM3352 Technical Reference Manual".

    Regards,

    Saravanan.K

  • 0 in reply to Saravanan Karivandan1
    TI__Mastermind 27890 points

    The answer is "both". This is echoed in my response to your other post:

    RE: USB host without VBUS and DRVVBUS