While the analog functions of Concerto draw power from a single dedicated external power source—VDDA, its digital circuits are powered by three separate rails: 3.3-V VDDIO, 1.8-V VDD18, and 1.2-V VDD12. This section describes the sourcing, regulation, and POR functionality for these three digital power rails.
Concerto devices can be internally divided into an Analog Subsystem and a Digital Subsystem (having the Cortex-M3-based Master Subsystem and the C28x-based Control Subsystem). The Digital Subsystem uses VDD12 to power the two processors, internal memory, and peripherals. The Analog Subsystem uses VDD18 to power the digital logic associated with the analog functions. Both Digital and Analog Subsystems share a common VDDIO rail to power their 3.3-V I/O buffers through which the Concerto digital signals communicate with the outside world.
The Analog and Digital Subsystems each have their own POR circuits that operate independently. With the ARS and XRS reset pins externally tied together, both systems can come out of reset together, and can also be put in reset together by driving both reset pins low. See Figure 6-6 for a snapshot of the voltage regulation and POR functions provided within the Analog and Digital Subsystems of Concerto.