Information

Description STM32F405xx, STM32F407xx
26/185 DocID022152 Rev 4
Two external ceramic capacitors should be connected on V
CAP_1
& V
CAP_2
pin. Refer to
Figure 21: Power supply scheme and Figure 16: VCAP_1/VCAP_2 operating conditions.
All packages have regulator ON feature.
Regulator OFF
This feature is available only on packages featuring the BYPASS_REG pin. The regulator is
disabled by holding BYPASS_REG high. The regulator OFF mode allows to supply
externally a V
12
voltage source through V
CAP_1
and V
CAP_2
pins.
Since the internal voltage scaling is not manage internally, the external voltage value must
be aligned with the targetted maximum frequency. Refer to Table 14: General operating
conditions.
The two 2.2 µF ceramic capacitors should be replaced by two 100 nF decoupling
capacitors.
Refer to Figure 21: Power supply scheme
When the regulator is OFF, there is no more internal monitoring on V
12
. An external power
supply supervisor should be used to monitor the V
12
of the logic power domain. PA0 pin
should be used for this purpose, and act as power-on reset on V
12
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 V
12
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.
Figure 9. Regulator OFF
ai18498V4
External V
CAP_1/2
power
supply supervisor
Ext. reset controller active
when V
CAP_1/2
< Min V
12
V
12
V
CAP_1
V
CAP_2
BYPASS_REG
V
DD
PA0 NRST
Application reset
signal (optional)
V
DD
V
12