STM32F401CB datasheet(21/134 Pages) STMICROELECTRONICS

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Functional overview

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DocID024738 Rev 5

3.15.1

Regulator ON

On packages embedding the BYPASS_REG pin, the regulator is enabled by holding

BYPASS_REG low. On all other packages, the regulator is always enabled.

There are three power modes configured by software when the regulator is ON:

•

MR is used in the nominal regulation mode (With different voltage scaling in Run)

In Main regulator mode (MR mode), different voltage scaling are provided to reach the

best compromise between maximum frequency and dynamic power consumption.

•

LPR is used in the Stop modes

The LP regulator mode is configured by software when entering Stop mode.

•

Power-down is used in Standby mode.

The Power-down mode is activated only when entering in Standby mode. The regulator

output is in high impedance and the kernel circuitry is powered down, inducing zero

consumption. The contents of the registers and SRAM are lost.

Depending on the package, one or two external ceramic capacitors should be connected on

the VCAP_1 and VCAP_2 pins. The VCAP_2 pin is only available for the LQFP100 and

UFBGA100 packages.

All packages have the regulator ON feature.

3.15.2

Regulator OFF

The Regulator OFF is available only on the UFBGA100, which features the BYPASS_REG

pin. The regulator is disabled by holding BYPASS_REG high. The regulator OFF mode

allows to supply externally a V12 voltage source through VCAP_1 and VCAP_2 pins.

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

be aligned with the targeted maximum frequency. Refer to Table 14: General operating

conditions.

The two 2.2 µF VCAP ceramic capacitors should be replaced by two 100 nF decoupling

capacitors. Refer to Figure 18: Power supply scheme.

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.

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