DocID027559 Rev 5 11/54
AN4661 Power supplies
53
1.2 Power supply scheme
• V
DD
= 1.7 to 3.6 V: external power supply for I/Os and the internal regulator (when
enabled), provided externally through V
DD
pins. The V
DD
pins must be connected to
V
DD
with external decoupling capacitors: one single tantalum or ceramic capacitor
(min. 4.7 F) for the package + one 100 nF ceramic capacitor for each V
DD
pin.
• V
SSA
, V
DDA
= 1.7 to 3.6 V: external analog power supplies for ADC, DAC, Reset
blocks, RCs and PLL. V
DDA
and V
SSA
must be connected to V
DD
and V
SS
, respectively.
The V
DDA
pin must be connected to two external decoupling capacitors (100 nF
ceramic + 1 F tantalum or ceramic).
• V
DDUSB
can be connected either to V
DD
or an external independent power supply (3.0
to 3.6V) for USB transceivers. For example, when the device is powered at 1.8V, an
independent power supply 3.3V can be connected to V
DDUSB
.
The V
DDUSB
pin must be connected to two external decoupling capacitors (100 nF
ceramic + 1 F tantalum or ceramic).
• V
BAT
= 1.65 to 3.6 V: power supply for the RTC, the external clock 32 kHz oscillator and
backup registers (through power switch) when V
DD
is not present.
The V
BAT
pin can be connected to the external battery (1.65 V < V
BAT
< 3.6 V). If no
external battery is used, it is recommended to connect this pin to V
DD
with a 100 nF
external ceramic decoupling capacitor.
Note: V
DD
/V
DDA
minimum value of 1.7 V is obtained when the internal reset is OFF (refer to
Section 1.3.5: Internal reset OFF).
• The V
REF+
pin can be connected to the V
DDA
external power supply. If a separate,
external reference voltage is applied on V
REF+
, a 100 nF and a 1 F capacitors must be
connected on this pin. In all cases, V
REF+
must be kept between (V
DDA
-1.2 V) and
V
DDA
with minimum of 1.7 V.
• Additional precautions can be taken to filter analog noise:
–V
DDA
can be connected to V
DD
through a ferrite bead.
–The V
REF+
pin can be connected to V
DDA
through a resistor (typ. 47 ).
• For the voltage regulator configuration, there is a specific BYPASS_REG pin (not
available on all the packages) that should be connected either to V
SS
or V
DD
to activate
or deactivate the voltage regulator specific.
Note: Refer to the voltage regulator section of the related device datasheet for more details.
• When the voltage regulator is enabled, VCAP1 and VCAP2 pins must be connected to
2*2.2 F low ESR < 2
ceramic capacitor. In the STM32F7x2Rx devices, only the
VCAP1 pin is available and must be connected to 4.7
µF low ESR between 0.1 and
0.2
ceramic capacitor.
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