NUCLEO-F207ZG / STM32F207ZG supply voltage

Question

I need to change the wait states via the Flash access control register for an STM32F207ZG on a NUCLEO-F207ZG board.

The reference manual gives a table that tells you how many wait states you need based on the clock frequency of the cortex M3 in MHz and the 'supply voltage of the device'. But how do I determine the correct voltage range?? The voltage ranges given are "2.7 to 3.6", "2.4 to 2.7", "2.1 to 2.4" and "1.8 to 2.1 V. The supply voltage to the board is 5V over Usb but that is not mentioned in the table. I assume the board drops some voltage to step it down to what the stm32 chip requires. However I can't find any mention of what that voltage is and so I'm at a complete loss as to which voltage range I need to select.

Answer 1

The schematics for this board show that the VDD net is connected to +3V3 via JP5, so unless you've removed that link to provide another supply, we can assume that VDD=+3.3v.

As you mention, the number of wait states depends on the core frequency, and voltage at VDD.

The datasheet for the part states that for "VDD=2.7 to 3.6V", you can access the flash at up to 30 MHz with 0 wait states, increasing to 3 wait states at ~90MHz or above.

I've included Figure 21 from the datasheet below, but Table 15 is also relevant.