TUSB8042A: TUSB8042A Enable Sequence

Hi Billy,

USB_VBUS should only be asserted high if the USB Host is ready to communicate with TUSB8042A and not before. VDD1.1 or VDD3.3 could be used using a combination of a resistor divider and a pull down capacitor (connected directly to USB_VBUS) to ensure that USB_VBUS is asserted after USB Host is ready to communicate.

Hi Malik

Thanks for the comments.

The issue is happening with QCom Platform during image download w/o the USB_VBUS.

It seems that it is working w/o the USB_VBUS if they remove the resistor divider and pull down capacitor. 

Is it possible to remove the divide resistor and pull down capacitor w/o any issue except for ensuring the assertion of the USB_VBUS?

Please review and let me get your advice on this.

Thanks and Best Regards

Billy Yun

Hi Malik

Thanks and Let me add some more questions on the issues.

Q1. Reference Design

Could you review on whether the connections between AP and USB3.2 Gen1 of TUSB8042A (Q1 in Attachment) are correct or not? 

This is the connection of TUSB8042A's USB_SSTX_UP to AP's USB_SSRXP_AP

Q2 Is there any possibility to be shown 50Ohm term. when there's no power supply to TUSB8042A?

This is because AP TX transit to USB3.2 Gen1 Compliance mode with PA's USB_SSTXP signal is connected to HUB's SSTXP_UP

oscilloscope shot and connection are in the attachment in Q2.

Please review and let me get your advice on this.

Thanks 

Billy Yu

TUSB8042 Questions.pptx

Hi Malik

Thanks and Let me add some more questions on the issues.

Q1. Reference Design

Could you review on whether the connections between AP and USB3.2 Gen1 of TUSB8042A (Q1 in Attachment) are correct or not? 

This is the connection of TUSB8042A's USB_SSTX_UP to AP's USB_SSRXP_AP

Q2 Is there any possibility to be shown 50Ohm term. when there's no power supply to TUSB8042A?

This is because AP TX transit to USB3.2 Gen1 Compliance mode with PA's USB_SSTXP signal is connected to HUB's SSTXP_UP

oscilloscope shot and connection are in the attachment in Q2.

Please review and let me get your advice on this.

Thanks 

Billy Yu

8726.TUSB8042 Questions.pptx

Hi Billy,

TUSB8042A cannot connect to the AP without USB_VBUS going high. Is this pin being controlled at all? Is there a waveform for USB_VBUS and voltage rails at power-up?

I suspect that the AP terminations are left on and the compliance pattern is actually coming from TUSB8042A. This is standard operation for the upstream port of the USB Hubs which output compliance pattern automatically when terminations are presented with no LFPS form the USB Host.

The SSTX & SSRX connection from the attachment is correct. 

Hi Malik

Thanks for the feedback.

And the main issue is not to have the USB_VBUS for image download operation but need to power up the TUSB8042A.

Is there any way to power up without the USB_VBUS?

And you mean that it can be working with the output compliance pattern even though there's no VDD1.1 & 3.3 with VBUS in the previous attached image in Q2?

Please review and let me get your advice on those above as well.

Thanks for your help.

Thanks and Best Regards

Billy Yun

Hi Billy,

TUSB8042A can be powered up (GRSTZ , 3.3V rail, 1.1V rail goes high) but USB_VBUS is necessary for connection on the upstream port. 

I misunderstood your question. If TUSB8042A is not powered receiver termination is off.