Hi Dawei,
Regarding the following comment - "we have external regulators to generate 1.2V/1.8V/3.3V from VBUS pin of USB connector, which supplies FX3. VBATT is supplied with 3.3V, and FX3 VBUS (E11) is directly connected to VBUS of USB connector. So in this case, does FX3 draw any current from VBUS pin (E11)?"
>>I see that since VBUS pin of FX3 is connected from VBUS pin of connector and the IO power domains of FX3 are derived from VBUS pin of the connector (via regulators) - FX3 draws current from VBUS line.
For your information I mention the following:
Below two are the default cases:
a. USB Block of FX3 is powered by VBUS.
b. VBUS detection(which is necessary for a USB compliant device) is also done using VBUS pin voltage.
So, if VBUS from the USB connector is connected to VBUS pin then the USB block draws current from VBUS line. And at the same time if all the IO powers is also derived from this VBUS, then all the IOs and the USB block draws current from VBUS.
But, when you use the API CyU3PUsbVBattEnable(CyTrue), then the USB Block will be powered by VBATT pin voltage instead of VBUS.
Using CyU3PUsbControlVBusDetect(CyBool_t enable, CyBool_t useVbatt):
a. VBUS detection can be made to happen using VBATT pin (In this case useVbatt is set to true)
b. By making both the above parameters false, VBUS can be connected to a GPIO and necessary handling can be done in the firmware. (This case is irrelevant in your case since you are not doing it)
Regarding the ESD strike case:
VBUS pin is not expected to get voltage above 6V even during ESD scenario. Main cause for the ESD strike at VBUS pin would be a. User touching the USB connector b. Device Hot plug to the Host. In both of these cases OVP IC would be protecting the VBUS pin. That is the reason I had suggested it before.
Please let me know your comments.
Regards,
Hemanth
Hemanth
