Potential voltage confliction while stacking two CYUSB3KIT-003

[WGT_4383351]

If one kit is connected to USB and another still not connected (or one host PC is down), then some pins on GPIF II bus may be driven by the powered kit onto the unpowered kit which may be harmful unless the firmware and the GPIF II state machine can be sure that this doesn't happen.

A potential solution is remove VBUS jumper of one kit and connet USB3_VBUS between the kits by not cutting that pin. Potential problem is this may drive VBUS_IN on the unpowered kit trough U11 to 4.x Volts.

[YashwantK_46]

Hi,

Can you please explain about the interconnection between the kits? Which pins are being connected between the two kits?

Also, can you please elaborate as to how you tested the conflict?

And what do you mean by the following: connet USB3_VBUS between the kits by not cutting that pin.?

Regards,

Yashwant

[WGT_4383351]

The default connection is as described in 001-87216_AN87216_Designing_a_GPIF_II_Master_Interface, section 8, Fig. 25~27.

I'v not tested them, it is a guess before the experiment which can harm the board if confliction exists.

Meaning of "connet USB3_VBUS between the kits by not cutting that pin.?" :

In 87216_AN87216, USB3_VBUS is cut as shown in Fig. 27. So if it is not cutted, the USB3_VBUS of the two kit will be connected.

[YashwantK_46 · Accepted solution]

Hello,

We don't have information about the conflict that you pointed out.

From the schematics of the FX3 SuperSpeed Explorer Kit, I can point out that there wont be harm to try the solution that you have specified.

But, doing so will make the unpowered kit conclude that it is getting VBUS from the host and tries to perform certain USB specific functions which will fail causing an overall USB communication failure.

Also, if you short USB3_VBUS between two kits and disconnect VBUS_JUMPER, the firmware,if loaded into the EEPROM or FLASH, would be loaded into the RAM of FX3's and the application will start without the second kit enumerating at the host side. If you want the second kit to enumerate, you will have to make sure that you will need to disconnect the shorted USB3_VBUS between the two kits before connecting the VBUS_JUMPER of the second kit.

One more issue that I can point out would be the fact that both the kits are being powered by the same USB lines and if the current consumption increases on the USB bus, the host controller will cut off the VBUS to both the devices to protect the host.

"A potential solution is remove VBUS jumper of one kit and connet USB3_VBUS between the kits by not cutting that pin. Potential problem is this may drive VBUS_IN on the unpowered kit trough U11 to 4.x Volts."

--However, if this potential solution is implemented and the VBUS of both the kits is connected, this may drive the VBUS_IN on the unpowered kit, but it won't make any difference as long as the VBUS_JUMPER is disconnected on the board. But if the VBUS_JUMPER is connected on the board, there is a chance of the entire board to be shorted out including the LDO's and the FX3 chip itself.

Regards,

Yashwant