Separate supply specifically for a chip's input/output pins (can differ from core voltage).
How it looks
Real geometry: CORE3588 copper, drawn from our board file (2D plan view)
The pads of the motion sensor U11 (ICM-42688-P) on CORE3588, flat copper, 5.6 x 4.4 mm: two supply pins wired to two different rails. Pin nets read from our board file.
1Pin 5, VDDIO (amber): on the 1.8 V rail, the voltage the computer module's pins use.
2Pin 8, VDD (grey): on the 3.3 V rail, which runs the sensor's insides.
Real image: CORE3588, rendered by KiCad from our board file
The same spot rendered.
1The sensor itself sits on those pads; its pins are hidden underneath.
How it works
Where it fits
VDDIO is a second VDD rail just for the pins. Buses like SPI and I2C run at the VDDIO voltage.