AM5718: AM5718 USB2.0 port signal status during system power up

Hi Peng,

I was able to reproduce this issue on my AM571x IDK as well , I also see a short pulse on USB2_DP during power-up. I am not sure yet if this is expected behaviour or not; let me check internally and get back to you.

Regards,

Karthik

Hi, Karthik,

Any update from your team?

Regards,

Peng,

Hi Peng, (Karthik),

Is the pulse on USB_DP causing issues in your system?  Can you compare the timing of that pulse relative to a) power-up sequence and reset de-assert, or b) relative to some boot code execution?  

Thanks,

Kyle

Is there any issue when you insert a USB 2.0 device (not detected or enumerated)?

Usually, D+ pulled high is part of the enumeration process when the device is inserted and it indicates to the host that its a USB2.0 HS device.

but interestingly enough you have mentioned that it is going high even before device is inserted. I think in host mode, the Vbus is always high.

Hi, Karthik,

When this D+ pulse happens, the VBUS has not come up yet (see attached picture below).

On PCA, there is no external pull-up resistors and no external active component connected to D+ trace from AM5718 chip and USB port connector.

Recently there are some downstream device USB port damage cases (The device is connected to the host always, and powers up with host). The device supplier suspects the unexpected pulse on D+ before VBUS comes up could damage the device.

Peng,

Is this observed on all devices and is it only happening at power-up? 

It may be that during the power up, the host's pullup / pulldown resistors are not yet setup; or the host may be polling for a device being inserted or not to have the momentary pulse. It should not have consequences on the downstream USB port being damaged if the circuit has been designed as per specs.

Are you observing enumeration failures when a device is inserted but not detected at all?

How does the scope shots look when a USB 2.0 device is inserted? I am hoping that the VBUS should go high and the D+ would also follow by going high to initiate the high-speed handshake?  

Hi Shreyas,

This is observed on all devices during power-up, also observed on AM571x IDK.

We observed client device damage, and the device supply thinks this pulse violates the USB port power-up sequence and could damage the chip.

Peng,

Do you have the scope shots when the device is inserted? Are all the USB devices being damaged? 

The device pulse is within the USB specs of 3.3V, the 3V I think indicates that the 1.5k pullup / 15k pulldown are active?

Hi, Shreyas,

This pulse is from AM5718 during its power up w/o client device physically connected. It is AM5718's own behavioral, not relevant to external client device's pull-up.

Hi Peng,

When you boot up the EVM, can you boot it in the noboot mode and see if the pulse goes away? 

and can you also bypass the power switch, so that you have the Vbus on as you power up, without waiting for the USBDRVBUS signal? This is assuming that you are always in the host mode. 

As said in the question description, the AM5718 GPIO7_24 (ID) is pulled-down to GND with 10K resistor. Isn't it always in host mode?

Since TI has reproduced this issue using the AM571x IDK, TI will conduct its own investigative tests and provide the customer with a clear answer.

Peng,

At this time, I do not have an answer for you. We took a look at an errata on a similar device, which mentioned the D+ pulse, and the workaround for it; however, the charge detection circuit is disabled on this device during boot by default.

The next step is to do some more research into this. Meanwhile, one of the suggestions was to bypass the power switch so as to have the Vbus power to the device side, as this is set to be always in host mode. 

I also got confirmation that the pulse is within 3V and will not damage the AM57x USB port/Controller.

Hi Peng Liu50174,

Add to what ShreyasRao mentioned, we have a few questions to understand the issue:

- When you "During AM5718 power up", is this during cold power-on reset (POR)?

- If yes, what sysboot setting is used during this time?

- What is the AM5718 USB0 usage on your product? 

Peng Liu50174 said:

Recently there are some downstream device USB port damage cases (The device is connected to the host always, and powers up with host). The device supplier suspects the unexpected pulse on D+ before VBUS comes up could damage the device.

- What software is being used on the AM5718 side? Can you share the details? Also, please share more details on your analysis on the downstream device USB port damage and why it could not be the issue on the downstream device side?

Thanks.