Parallax P2 Edge Module - User Guide

2. VDD Power Supply with reverse polarity input protection

The VDD power supply is for the Propeller 2 core. This onboard power supply is based on a

switching buck regulator, capable of delivering 2 A at 1.8 V. Short circuit, over-current,

reverse-input polarity and brownout detection are also included.

VDD is typically expected to be 1.8 V. This voltage powers the internal circuits of the P2

microcontroller. In case of a serious prolonged short-circuit or over-voltage condition, the VDD

regulator will shutdown and remain locked off to prevent any serious damage. In this case, the

short-circuit should be remedied, and then the power supply will need to be power-cycled to

attempt a restart. If the fault remains, then the VDD regulator will immediately go into the

shut-down and locked off state again.

The VDD power supply includes Brown-out Detection, which will keep the P2 in reset whilst

VDD is below approximately 1.5V.

3. LDO regulators for I/O Pin Voltage

The 8 LDO regulators are fixed 3.3 V low-noise regulators, which power the P2 I/O smart-pins.

Each regulator has short-circuit and over-current protection. You may see this voltage referred

to as VIO (Voltage for IO), or by group of I/O pins in the format Vxxxx or Vxx.

At the actual microcontroller, the Propeller 2 Smart I/O pins are grouped such that each 4 I/O’s

have a dedicated voltage supply connection. If you refer to the diagram Propeller 2 Physical Pins

you will see the voltage supply connections labelled as V0003, V0407, V0811, etc.

This allows pins that will be performing sensitive analog functions to use dedicated quiet, local

3.3 V regulation.

With the P2 Edge Module, the voltage supply connections have been brought out in groups of 8

I/O pins each. Each group has a dedicated LDO regulator with the VIO output labelled Vxx at the

edge connector. The two digits after the V refer to the first of 8 I/O pins that the LDO provides

power to. For example, V08 would mean VIO voltage for I/O pins 8 to 15.

Note: While it would be possible (and typical) to have a single larger regulator to power all the

3.3 V I/O supplies, the distributed LDOs allow for better local regulation, higher current and

isolation per I/O group, low noise, improved protection, less voltage drop under load, and

better thermal characteristics. The distributed power scheme is not a requirement of the P2

microprocessor; rather a design choice for this particular module.