Are USB-Serial (CY7C6521x) family devices pin-for-pin-compatible with USB-UART (CY7C64225)?
No. CY7C6521x family devices are not intended to be pin-for-pin-compatible with the previous-generation USB-UART (CY7C64225) device. For all new designs that require a single USB-UART interface, Cypress recommends CY7C65213 because it has superior features, such as higher performance, lower power consumption, battery charger detection, and internal flash memory. CY7C65213 comes in a 32 pin QFN package (5 mm x 5 mm), while the CY7C64225 comes in a 28-pin SSOP package (10 mm x 7.5 mm).