Cypress Perform

Answer: Cypress does not recommend mixing power modes in a single design.

The CY7C64225 can operate using a single 5 V or 3.3 V power supply. 5 V operation is easy to integrate into designs that use the upstream USB supply (bus powered) to power the entire design. The voltage specification of the supply pin and the VBUS pin (4.75 to 5.25 V) in the USB specification are the same. 3.3 V operation is easy to integrate into designs that already have an onboard 3.3 V regulator.

The CY7C64225 uses the VBUS pin for VBUS (upstream USB supply) monitoring.
 

• For self-powered devices, connect the VBUS pin to the upstream USB supply pin with a 1 kΩ resistor in series.
• Because bus-powered designs power down when unplugged from the USB port, they do not require the monitoring of the upstream VBUS. Therefore, connect the VBUS pin to logic high (or upstream USB supply) through a 1 kΩ resistor.