De-activating the Core Voltage Regulator to Perform Power Analysis on STM32F407 DISCOVERY Board

Question

I am trying to perform Power Analysis (Side-Channel Attack) on AES-128 that I have implemented on STM32F407 DISCOVERY MCU. I have found out that I can measure with a current probe from VCap1 and Vcap2 . To do so, the regulator that feeds the core should be turned off and the processor should be fed with external power supply to minimize the noise. But the regulator is inside the core and I cannot take it off. How can I de-activate the regulator? Or is there any other way to perform Power Analysis on STM32F407VG MCU?

Answer 1

I afraid it is not possible. The voltage regulator has to be on otherwise the core and peripherals clocks will not work. There is no way to switch this regulator off

You need to find another way.

Answer 2

The datasheet mentions that, on some packages, there is pin called BYPASS_REG which can be used to disable internal voltage regulator and allow you to supply core using V_CAP pins. See Section 2.2.16 Voltage Regulator in the STM32F407 datasheet (DS8626).

Unfortunately, STM32F407V present on Discovery Board isn't one of the packages which feature BYPASS_REG pin. This pin is present on WLCSP90, UFBGA176 and LQFP176 packages, according to Table 3. Regulator ON/OFF and internal reset ON/OFF availability.