AM625: Schematic Design Queries regarding USB interface

Sahil Nayak

Prodigy 220 points

Part Number: AM625

Hi TI Team,

We are working on AM6254 based custom design and want some clarification regarding the USB interface pins usage.

Use-case:

USB0 port will be used for USB DFU boot only.
USB1 port will be used to connect the cellular module (M.2 form factor).

List of queries:

As per our understanding, for both the USB ports, a voltage divider of 20K and 10K is sufficient (reference from the schematic checklist), as per the use-case as shown in the image below. Please confirm.
For Port 0, AM6254 will be in the USB device mode and for Port 1, AM6254 will be in USB host mode.

2. As per our understanding, as per our use-case, we won't require the USBx_DRVVBUS pin to be connected, so we have Test points on that pin. Please confirm.

Please provide your input for both points.

Thanks & Regards,
Sahil Nayak

3 months ago

0 Stanislav Stilyanov 3 months ago

TI__Mastermind 24990 points

Hi Sahil,

1. For USB0 (device mode), I would recommend to connect USB0_VBUS it to VBUS pin of the USB receptacle. I'm not sure if ROM strictly requires it, but even it don't, you might need to use the port for a generic USB connection or for debug.

For USB1 (host mode to M.2), you can connect VBUS-sense pin it to permanent 5 volts, or 3.3 V with proper resistors.

2. DRVVBUS is only used in host mode, and my understanding is that power supply to M.2 is uninterruptible or at least not by USB controller.

Regards,

Stan

0 Sahil Nayak 3 months ago in reply to Stanislav Stilyanov

Prodigy 220 points

Hi Stan,

Thank you for your quick response.

For both USB0 and USB1, can we connect 3.3V to USBx_VBUS pins with proper resistors? 5V will be the source voltage and with a resistor divider, 3.3V would appear at the USBx_VBUS pins.
Will that work for both cases?

0 Stanislav Stilyanov 3 months ago in reply to Sahil Nayak

TI__Mastermind 24990 points

Hi Sahil,

USB1 (host mode) : USBx_VBUS pin is not actively used by the controller. Te recommended usage is to connect it to 5V div by 3 - your snapshot. Or, to 3.3V div by 2.

USB0 (device mode): The recommendation is to take VBUS from the USB receptacle pin and divide it by 3 then route it it to USB0_VBUS.

Regards,

Stan

0 Sahil Nayak 3 months ago in reply to Stanislav Stilyanov

Prodigy 220 points

Hi Stan,

Please see the attached image (updated power rail for the USB0_VBUS) as per your recommendations:

VBUS_5V will be coming from the Host PC for the USB0 port.

So, the voltage at both USBx_VBUS pins will be ~1.67V (5V div by 3).

Let me know if there are any changes required to be made.

Thanks & Regards,
Sahil Nayak

+1 Stanislav Stilyanov 3 months ago in reply to Sahil Nayak

TI__Mastermind 24990 points

Sahil,

My understanding is that you don't have an USB power delivery (PD) controller in your project. Is this correct? If correct, then yes this is fine.

Regards,

Stan

0 Sahil Nayak 3 months ago in reply to Stanislav Stilyanov

Prodigy 220 points

Hi Stan,

We don't have a requirement for PD.

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AM625: Schematic Design Queries regarding USB interface