Datasheet

DocID027107 Rev 6 23/202
STM32F446xC/E Functional overview
40
Figure 5. V
DDUSB
connected to an external independent power supply
3.16 Power supply supervisor
3.16.1 Internal reset ON
On packages embedding the PDR_ON pin, the power supply supervisor is enabled by
holding PDR_ON high. On the other package, the power supply supervisor is always
enabled.
The device has an integrated power-on reset (POR)/ power-down reset (PDR) circuitry
coupled with a Brownout reset (BOR) circuitry. At power-on, POR/PDR is always active and
ensures proper operation starting from 1.8
V. After the 1.8 V POR threshold level is
reached, the option byte loading process starts, either to confirm or modify default BOR
thresholds, or to disable BOR permanently. Three BOR thresholds are available through
option bytes. The device remains in reset mode when V
DD
is below a specified threshold,
V
POR/PDR
or V
BOR
, without the need for an external reset circuit.
The device also features an embedded programmable voltage detector (PVD) that monitors
the V
DD
/V
DDA
power supply and compares it to the V
PVD
threshold. An interrupt can be
generated when V
DD
/V
DDA
drops below the V
PVD
threshold and/or when V
DD
/V
DDA
is
higher than the V
PVD
threshold. The interrupt service routine can then generate a warning
message and/or put the MCU into a safe state. The PVD is enabled by software.
3.16.2 Internal reset OFF
This feature is available only on packages featuring the PDR_ON pin. The internal power-on
reset (POR) / power-down reset (PDR) circuitry is disabled through the PDR_ON pin.
An external power supply supervisor should monitor V
DD
and should maintain the device in
reset mode as long as V
DD
is below a specified threshold. PDR_ON should be connected to
VSS, to allows device to operate down to 1.7v. Refer to
Figure 6: Power supply supervisor
interconnection with internal reset OFF.
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