[FAQ] AM6442, AM6441, AM6422, AM6421, AM6412, AM6411 Custom board hardware design – USB2.0 interface

Hi Board designers, 

1. Supported USB interface configuration. 

USB0 interface supports Host or Device or Dual-Role (DRD)

2. Is the VBUS connection required for Host configuration or Device configuration.

VBUS connection for Host interface is optional.

It is recommended to connect the VBUS when the USB interface is configured as Device.

The recommended voltage range is the divided voltage equivalent of 4.75 V - 5.25 V for normal operation.  

3. Can I have the VBUS supply input connected when the SoC power supply is switched off

USB VBUS IO is fail-safe. The VBUS input does not have any dependency on the SOC power supply.

4. Is there a power sequencing requirement for VBUS input. 

USB VBUS IO is fail-safe and do not have any sequencing requirements.

5. Can I connect 5 V input from the USB connector directly to VBUS input. 

VBUS pin cannot be connected directly to external/connector VBUS, as IO is not 5 V compliant. Recommend using voltage divider and/or current limiter to ensure IO requirements are met. VBUS pin can be consider fail-safe only if recommended external divider circuit is used.

Connection of 3.3 V directly to VBUS input is not allowed or recommended.

For USB Device interface, it is recommended to connect a switched external USB VBUS supply to the USB0_VBUS input of the SOC through recommended resistor divider.

6. Recommended VBUS supply voltage divider 

Refer section 9.2.3 USB VBUS Design Guidelines of the data sheet.

7. SOC VBUS input voltage range and Zener diode connection 

We do not define VBUS thresholds. VBUS thresholds are defined in the USB specification. The thresholds were designed to be compliant to the USB specifications and validated via USB-IF compliance tests.
The VBUS input has an ESD clamp to the 3.3 V rail. The USB VBUS Design Guidelines section of the datasheet defines the VBUS connection topology. This voltage divider / clamp circuit allows VBUS to go up to 30 V without harming the VBUS input. The Zener diode could be removed and a 20 KΩ resistor could be substituted for the 16.5 KΩ and 3.5 KΩ resistors if your system will never apply a VBUS potential greater than 5.5 V and the 5.5 V is sourced on-board.

8. Supported USB Backup bootmode configuration.

USB0 interface is recommended to be configured as a device. USB DFU backup mode works with 0.75 V SOC core supply.

9. Recommended USB RCALIB resistor 

Refer below section of the data sheet. 

6.3.25 USB, 6.3.25.1 MAIN Domain, Table 6-79. USB0 Signal Descriptions

RCALIB resistor should not exceed ±1% at any operating condition for the lifetime of the product.

10. How to deal with the USB unused pins 

Refer below section of the data sheet. 

6.4 Pin Connectivity Requirements, Table 6-80. Connectivity Requirements 

11. Is the USB0_ID connection required for Host configuration or Device configuration. 

It is recommended to connect USB0_ID pin to VSS through a 0 Ω resistor when the USB interface is configured as Host.

It is recommended to leave the USB0_ID pin floating when the USB interface is configured as Device.

For implementations that do require DRD functionality, connect USB0_ID pin directly to the corresponding ID pin on a USB Micro-AB connector. Depending on the cable attached, the USB0_ID pin will be terminated, and the processor will be configured as Host or Device.

12. Power supply switching and protection when the SOC is configured as USB Host

USB0_DRVVBUS can be used to control the power (load) switch. The USB interface or the Linux driver is not checking the status of VBUS to determine if there is a fault condition. In that case, you should connect the fault output of the VBUS power (load) switch to a GPIO and configure the GPIO to generate an interrupt that indicates there has been an over-current condition.

13. Are these recommendations valid for other Sitara processors or MCUs?

The recommendations are valid for the following family of devices:

AM243x

14. Do you have some recommendations on the Type-C implementation.

    AM64x EVM or SK does not have the implementation.

    Refer below starter kit for implementation.

    https://www.ti.com/tool/SK-AM62B-P1

15. Can I use 3.4K instead of 3.5K.

It should be Ok to use a 3.4K for the divider. It is recommended to select 3.48K value based on the availability.

16. Do the differential signal pins (oLDI, USB, etc.) have the capabilities to adjust the swing of the voltage?

No.

Note: 

Ensure the recommended capacitors are provided for the VBUS supply near to the connector (Host > 120 uF and Device (1-10 uF))

USB0_DRVVBUS has an internal pulldown enabled by default.

Refer below documents during the USB interface design.

Hardware Design Guide for AM6442, AM6422, AM6412 and AM2434 Processors

Hardware Design Guide for AM64x/AM243x Devices (Rev. A) (ti.com)

AM6442, AM6422, AM6412 and AM2434 Schematic Design and Review Checklist

AM64x/AM243x Schematic Review Checklist (Rev. B)

Regards,

Lavanya M R.