STM32F446RC datasheet(26/201 Pages) STMICROELECTRONICS

26 / 201 page

Functional overview

STM32F446xC/E

26/201

DocID027107 Rev 5

Since the internal voltage scaling is not managed internally, the external voltage value must

be aligned with the targeted maximum frequency. The two 2.2 µF ceramic capacitors should

be replaced by two 100 nF decoupling capacitors.

When the regulator is OFF, there is no more internal monitoring on V12. An external power

supply supervisor should be used to monitor the V12 of the logic power domain. PA0 pin

should be used for this purpose, and act as power-on reset on V12 power domain.

In regulator OFF mode, the following features are no more supported:

•

PA0 cannot be used as a GPIO pin since it allows to reset a part of the V12 logic power

domain which is not reset by the NRST pin.

•

As long as PA0 is kept low, the debug mode cannot be used under power-on reset. As

a consequence, PA0 and NRST pins must be managed separately if the debug

connection under reset or pre-reset is required.

•

The over-drive and under-drive modes are not available.

Figure 7. Regulator OFF

The following conditions must be respected:

•

VDD should always be higher than VCAP_1 and VCAP_2 to avoid current injection

between power domains.

•

If the time for VCAP_1 and VCAP_2 to reach V12 minimum value is faster than the time for

VDD to reach 1.7 V, then PA0 should be kept low to cover both conditions: until VCAP_1

and VCAP_2 reach V12 minimum value and until VDD reaches 1.7 V (see Figure 8).

•

Otherwise, if the time for VCAP_1 and VCAP_2 to reach V12 minimum value is slower

than the time for VDD to reach 1.7 V, then PA0 could be asserted low externally (see

Figure 9).

•

If VCAP_1 and VCAP_2 go below V12 minimum value and VDD is higher than 1.7 V, then a

reset must be asserted on PA0 pin.

Note:

The minimum value of V12 depends on the maximum frequency targeted in the application.

STM32F446RC датащи(PDF) 26 Page - STMicroelectronics