USB hosts hubs transceivers

[Anonymous]

Hello support team/community.

I am designing an USB 2.0 hub using the CY7C65642 TQFP48. It is for internal use, that´s why I don´t need an EEPROM or power control. It should be able to be selectively used as bus or self powered. So much for the basic conditions.

I used the reference scheme but still have some questions. Mainly just to be sure.

1. Why are capacitors only used for the downstream ports (VBUS)? Is that not necessary for the upstream?
2. Pin 25, 44: should 3.3V or 5V be used for high?
3. Pin 37: To differentiate between bus and self powered I would like to connect pin 37 to the external power supply (5V). Is 5V ok for that pin?
4. I found  a figure with information on what to do with unused pins here in the community, but nothing regarding unused pins in the datasheet.

          Pins for  OVR, PWR, pin 27 (no EEPROM used), all AMBER and GREEN pins : Since I don´t need any of this functionality is it ok to just not connect them or is it           better to connect them to GND? Only pins 24 and 33 need to be connected to GND (4 ports used), right?

   5. What are C1 and C2 in the formula on p. 5 „001-72332_AN72332_Guidelines_on_System_Design_using_Cypress_s_USB_2.0_Hub_HX2VL.pdf“

Thanks a lot!!

Sebastian

[YangyangC_06 · Accepted solution]

• Why are capacitors only used for the downstream ports (VBUS)? Is that not necessary for the upstream?

     >>Which capacitors are you referring to? Could you please make a screeshot to explain?

• Pin 25, 44: should 3.3V or 5V be used for high
• >>3.3V

• Pin 37: To differentiate between bus and self powered I would like to connect pin 37 to the external power supply (5V). Is 5V ok for that pin?

     >>Yes, it is ok.

• I found  a figure with information on what to do with unused pins here in the community, but nothing regarding unused pins in the datasheet. Pins for  OVR, PWR, pin 27 (no EEPROM used), all AMBER and GREEN pins : Since I don´t need any of this functionality is it ok to just not connect them or is it better to connect them to GND? Only pins 24 and 33 need to be connected to GND (4 ports used), right?

     >>If you don't use them you could just keep them float.

• What are C1 and C2 in the formula on p. 5 „001-72332_AN72332_Guidelines_on_System_Design_using_Cypress_s_USB_2.0_Hub_HX2VL.pdf“

     >>They are C11 and C12 in Figure 4

[Anonymous]

Hello.

I am reffering to the capacitors for the downstream ports VBUS. As you

see in the screenshot, the ferrit is used for up- and downstream (blue

circle) but the capacitors only for downstream (red circle). Can you

please explain me, why it is that way?

Thanks for all your answers!

Sebastian Reindl

[YangyangC_06]

Hi,

You could also add a capacitor on VBUS pin of upstream port. It will not be a problem.