I am currently designing a PCB using a PSoC 6, and I have questions regarding USB hardware configuration.
Considering the USB lines voltage of 5V, and the VDDUSB of the PSoC 6 of 3.3V, I wonder if I can connect the USB D+ and D- lines directly in the MCU since the voltage levels are not compatible. I can't find anywhere in the CYC61x7 datasheet any information about USBDM and USBDP lines being 5V tolerant …
The only thing of interest I can find is in the AN218241 document, but is not really of interest, and is quite vague actually … It states in section 10.2 (page 25) that:
When designing hardware for a USB Device, consider the following:
▪ Use ferrite beads for VBUS, GND, and receptacle shield.
▪ Use an ESD protection device placed near the USB receptacle.
I see in the CY8CKIT-062-WiFi-BT schematics that a USB multiplexer (NLAS7242MUTBG) is used to switch between Device and Host USB lines, and this IC is supplied with 3.3V. This IC datasheet clearly states that D+ and D- pins are Over Voltage Tolerant:
The NLAS7242 features over voltage tolerant I/O protection on the common signal pins D+/D−. This allows the switch to interface directly with a USB connector. The D+/D− pins can withstand a short to VBUS, up to 5.25 V, continuous DC current for up to 24 hours as specified in the USB 2.0 specification. This protection is achieved without the need for any external resistors or protection devices.
Do you have any recommendation regarding the hardware we have to use on USB lines of CYC61x7 MCUs to ensure proper functionality? Can anybody recommend a buffer IC that could be used for USB applications?
Please propose solutions that are not QFN, WLCSP or that kind of package which are harder to solder, I want it to be easily solderable ...
Thanks to all!
The PSoC 61 datasheet mentions that VDDUSB is the USB supply and is required to be 2.85 V to 3.6 V for USB operation. In addition, the pin powers Port 14 (which has the D+ and the D- lines) as shown below:
Thus we do not recommend you to connect USB D+ and D- lines directly to 5V.