[FAQ] AM6442, AM6441, AM6422, AM6421, AM6412, AM6411 and AM2434, AM2432, AM2431 (ALV, ALX) Custom board hardware design – USB2.0 interface

Hi Board designers, 

Additional inputs regarding USB RCALIB resistor implementation:

The IP specification TI received from the USB PHY design team defined a 500 ohm +/-1% calibration resistor. A few weeks ago another customer reminded us 500 ohms is not a standard value for 1% resistors. They were having problems sourcing a 500 ohm +/-1%, so asked if the could use a 499 ohm +/-1% resistor.

I ask the USB PHY team if we could change the recommendation from 500 ohm +/-1% to 499 ohm +/-1% to make resistor selection easier for our customers. They confirmed this would be okay, so we changed the recommendation in the datasheet.

I assume your board has two 1 kohm +/-1% resistors connected in parallel, and you are asking if this will be okay. This should be okay since the USB PHY was initially designed for a 500 ohm +/-1% resistor.

Regards,

Sreenivasa

Hi Board designers, 

Refer below section of the TRM for information related to USB2 polarity revu

• USB2 PHY:
– Fully compliant with UTMI+ Level 3 specification revision 1.0
– Supports high-speed (480 Mbps), full-speed (12 Mbps) and low-speed (1.5 Mbps) data rates
– Supports battery charging BC1.2v specification
– Supports host, peripherals and OTG 2.0 (dual role device) applications
– Supports D+/D- lane reversal for flexible board integration
– Supports USB low-power states; namely, suspend and link power management (LPM)
– Supports internal comparators for monitoring OTG voltage thresholds
– Supports multiple PLL reference clocks
– Supports internal PLL for high-speed (480 MHz) clock and data recovery (CDR) operation
– Integrated termination resistors (45 Ω, 1.5 KΩ, and 15 KΩ)
– Supports built-in self-test (BIST) for production testing
– 3.3-V ESD support on VBUS

Regards,

Sreenivasa

Hi Board designers, 

Refer below explanation for connecting the USB interface signals directly:

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/261717/am335x-series-resistors-on-usb_dp-usb_dm/914980?tisearch=e2e-sitesearch&keymatch=userdisplayname%25253A%252522Peaves%252522%252520%252526%252526%252520reflection#914980

According to the schematic checklist (processors.wiki.ti.com/.../AM335x_Schematic_Checklist of AM335x,

"USBx_DP and USB_DM should never have any series resistors or capacitance on these signals. These signals should be straight traces to the connector with no stubs or test points."

Can I know the reason why?

(observed problem)

* when connected 10 ohm series resistors (for avoiding ESD problem), error happened (at the driver) while transferring data through USB port

* when replacing it with 0 ohm, the error does not happen

* when comparing Eye-Patterns, there is no big difference (both meet the specification)

The additional 10 ohms of resistance creates an impedance mismatch in the transmission line.

This impedance mismatch causes a portion of the energy in the waveform propagating down the transmission line to be reflected. The reflection will be combined with data patterns propagating down the transmission line with the result being certain data patterns distorted beyond recognition. Some data patterns may be affected more than others due to many variables related to these reflections. It is possible the standard test packet may not be significantly affected by this impedance mismatch.

It is very important to maintain a 90 ohm differential transmission line to prevent any reflections.

Regards,

Sreenivasa

Hi Board designers, 

Inputs related to USBx_VBUS voltage 

Hi Board designers, 

Inputs related to use of Common Mode Choke

Page 11

USB3.0 USB2 common mode filter ACM2012-900-2P-T002

Common-mode chokes may be needed for EMI/EMC control. Note that these may reduce the signal amplitude and degrade performance.

https://www.ti.com.cn/cn/lit/an/sprack7b/sprack7b.pdf

https://www.ti.com/lit/an/sprabt8a/sprabt8a.pdf

Regards,

Sreenivasa

Hi Board designers, 

Inputs related to USB3 support and speed

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1273906/faq-am6442-am6441-am6422-am6421-am6412-am6411-custom-board-hardware-design---serdes---serdes0-interface

Regards,

Sreenivasa

Hi Board designers, 

Input related to USBx_RCALIB calib resistor

The USB port will have undefined behavior if it doesn’t have the proper calibration resistor connected. The USB port will have undefined behavior if it doesn’t have the proper calibration resistor connected.
Operating without the proper calibration resistor is not a valid use case. 

The calibration resistor is a reference standard that is used by the PHY calibration circuits to adjust voltage thresholds, IO impedances, and internal bias points of the analog circuits implemented in the PHY.

 Regards,

Sreenivasa 

Hi Board designers, 

Inputs related to USB interface.

I would like to use the USB function only for as a device, not host,  please tell me the following two points.
・Is it correct that CC1 and CC2 pins that come in from the outside are pulled down with 5.1kΩ?
・Is it correct that set the AM64x pin (U16, USB0_ID) as not connect?

AM64x does not have USB CC pins. It requires a companion device to implement USB Type-C.

Connecting 5.1K ohm resistors from each USB Type-C CC pin to ground defines an Up-stream Facing Port (UFP), which defaults to device mode. You need to select a USB Type-C companion device and connect it as described in the respective device datasheet.

The AM64x USB0_ID should be open-circuit when you are wanting the AM64x USB port to operate in device mode, or connected to ground when you are wanting the AM64x USB port to operate in host mode,  Note: You should never connect the USB0_ID pin to a circuit capable of sourcing current.  The USB0_ID pin should only be connected to a circuit that sinks current.

A UFP is expected to monitor the voltage of the CC pins to determine current sourcing capabilities of the DFP. The detection thresholds are 0.2V, 0.66V, and 1.23V. The DFP is capable of sourcing 500mA if USB 2.0 or 900mA if USB 3.0 when the UFP detects a voltage between 0.2V and 0.66V. The DFP is capable of sourcing 1.5A when the UFP detects a voltage between 0.66V and 1.23V. The DFP is capable of sourcing 3.0A when the UFP detects a voltage greater than 1.23V.

For this use case, you should be able to use the USB0_DRVVBUS pin as GPIO1-79 if you need another GPIO. However, this pin has an internal pull-down that is turned on by defaults, so you may need to account for it if you use the pin as a GPIO.

Monitoring the voltage of the CC pins may not be required if you are not using VBUS to power any circuits in your system. I recommend you confirm this is the case by reading the USB Type-C specification.

VBUS is not used to power the circuits in the system.
In this application, it is used only as a device, so I understand that the CCpin should be a 5.1k pull-down.
Please let me know if there is any discrepancy in my understanding.

I think you are okay with these connections.

I have some questions about connections between AM64 and TUSB320LA.

Q1: What is absolute maximum voltage on USB0_ID pin?

I'm going to skip this question for now because I do not think it is relevant.

Q2: What is the first power source of USB0_ID pin from outside? Three source are written in datasheet.

I'm going to skip this question for now because I do not think it is relevant.

Q3: What is the threshold voltage for Low detection on USB0_ID pin? 

You should never apply any potential to this pin. This pin should only be connected to a resistor that is connected to VSS. There is a an internal circuit that measures the resistance of this pin to VSS. Different resistor values are used to indicate the USB mode of operation and the resistors values are defined in the USB specification.

Q4: Is it able to connect the ID output of TUSB320LA to AM64 USB0_ID pin?

Only if the TUSB320LA output looks like a resistor connected to VSS and does not source any potential to the pin.

Q5: Is it able to pull the USB0_ID pin Low by TUSB320LA?

Only if the TUSB320LA output looks like a resistor connected to VSS and does not source any potential to the pin.

Q6: Now we connect the PU resister in USB0_ID line. Is it okey?

What is the threshold resistance to detect High or Low on ID pin?

It seems that the open drain resistance of TUSB320 ID pin is 250 ohm, according to the datasheet (Max. Low-level output voltage of open drain is 0.4 V at -1.6 mA). Mr. Nagata taught me that.

I have inserted a snapshot of valid ID resistor values as defined by USB-IF.

I do not think you will have a problem with the impedance of the TUSB320 ID pin being able to indicate host function (RID_GND).  However, you need to be careful with one of the recommendations mentioned in the TUSB320 datasheet.

The datasheet recommends the ID pin be connected to an external 200k ohm pull-up that is connected to the TUSB320 VDD 5V supply. This is a very bad recommendation without additional warnings related to potential EOS concerns when connected to devices like AM64x that cannot tolerate external sources, especially 5V sources. It is very likely the recommended circuit topology would destroy AM64x.

The TUSB320 ID pin is not fail-safe and they do not want you to apply any potential to it when the device is not powered. The AM64x ID pin has an internal current source that will be turned on when software initiates a ID resistance measurement. The ID resistance measurement should never be performed while the TUSB320 device is not powered to prevent the AM64x device from sourcing current into the TUSB320 ID pin which is not fail-safe. This is something you need to understand and implement appropriate system level precautions that prevent this from occurring.

I was not able to find the table of snapshot in datasheet version 3. Are you going to include the documents in the next datasheet version?

We only reference the respective USB and PCIe specifications in the datasheet for these industry standard interfaces since AM64x is compliant to the standards.

• Does the USB controller  for AM64x have ID pin?

Yes, AM64x has a pin named USB0_ID. See the AM64x datasheet.

(+) USB host and Peripheral modes operation - Processors forum - Processors - TI E2E support forums

Regards,

Sreenivasa

Hi Board Designers,

Inputs related to VBUS connection

regards,

Sreenivasa

Hi Board designers, 

Refer additional inputs 

(+) TUSB321: Query on USBC_ID pull-up value - Interface forum - Interface - TI E2E support forums

TUSB321: Query on USBC_ID pull-up value