I am designing a USB hub using USB3503 IC. I am trying to configure it without the need of programing its internal registers. Just by using its default settings. I want my windows 10 to recognize the USB hub, once I connect it to the PC's USB.

I am not 100% sure what is the correct way to connect the power supply pins, because the datasheet does not mention how the connections VDD33_BYP_1 and VDD33_BYP_2 should be hooked up. It mentions the VDD33_BYP pin as one pin, while the IC has two VDD33_BYP pins.

Same goes with VDD12_BYP_1, VDD12_BYP_2, VDD12_BYP_3 pins. The datasheet mentions only the powering of VDD12_BYP pin, while there are three of them.

All my connections are shown below:


simulate this circuit – Schematic created using CircuitLab

Using the above hookup, Connecting the USB hub to my PC, windows do not try to recognize it and do not pop up any message. And using my USB analyzer, I only see 0.01V on the data lines (which fluctuates, it becomes 0.00V sometimes).

enter image description here

Regarding the different behavior of each power pin:

Not all VDD12_BYP pins behave the same way and not all VDD33_BYP pins behave the same way. For example VDD33_BYP_1 gives an output of ~3.1V when VBAT is connected, but VDD33_BYP_2 does not give an output voltage.

Also, VDD12_BYP_3 pin does not output any voltage on its own in any hookup/connections. In contrary, VDD12_BYP_1 and VDD12_BYP_2 do output ~1.2V when VDD_CORE is biased with ~>=1.8V. The datasheet does not say if I need to connect/short the VDD12_BYP_3 with the other two VDD12_BYP pins. I have shorted the VDD12_BYP_3 with the VDD12_BYP_1 and VDD12_BYP_2, so that is gets biased with 1.2V.

As I have designed a couple of USB hubs at the past, I know that there are cases where I should not bias voltage into specific VDD pins, as they are used for internal logic and bias their own voltage when they need it on that specific VDD pin. But all of those USB hub datasheets never mentioned that this Pin should not be biased from outside sources..


1 Answer 1


Answering my own question.

Turns out I was trying to make use of the HSIC upstream of this USB hub, by connecting its upstream to my PC directly. But HSIC is not compatible with regular USB protocol.

special thanks to @pjc50 for answering this other question of mine and cleared some things.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.