Power supplies AN4938
8/46 AN4938 Rev 4
• When an OPAMP is used, V
DDA_MIN
equals 2.0 V.
• When a reference voltage (VREFBUF_OUT) is provided by the device on V
REF+
pin,
V
DDA_MIN
depends on the required level for this voltage.
Note: Refer to the product datasheets for more details on V
REF+
reference voltage range.
2.1.2 USB transceiver independent power supply
There are different ways to supply the USB transceivers, depending on VDD33USB and
VDD50USB availability:
• When the VDD50USB pin is available, this p
in can be used to supply an internal
regulator dedicated to USB transceivers. In this case, VDD50USB pin should receive a
voltage ranging from 4.0 to 5.5 V, typically supplied from the VBUS line of the USB
conn
ector. The regulated power (3.0 to 3.6 V) is available on VDD33USB.
In this configuration V
DD50USB
voltage must respect the following condition:
An external capacitor must be connected to VDD33USB.
• When the VDD33USB pin is available, this p
in can be used to supply the internal
transceiver. In this case, VDD33USB pin should receive a voltage ranging from 3.0 to
3.6 V. If VDD50USB is also available, it mu
st be connected to VDD33USB. As an
example, when the device is powered at 1.8 V, an independent 3.3 V power supply can
be
applied to VDD33USB.
When VDD33USB is connected to a separate power supply, it is independent from V
DD
and V
DDA
. It must be the last supply applied and the first supply switched OFF. The
following conditions must be respected (see Figure 2):
– During the power-on and power-down phases (V
DD
< V
DD
minimum value),
V
DD33USB
should always be lower than V
DD
.
–V
DD33USB
rising and falling time specifications must be respected (refer to table
power-up/power-down operating conditions (regulator ON) and table power-
up/power-down operating conditions (regulator OFF) provided in the device
datasheets).
– In operating mode, V
DD33USB
can be either lower or higher than V
DD
:
If a USB interface is used (USB OTG_HS/OTG_FS), the associated GPIOs
powered by V
DD33USB
operate between V
DD33USB_MIN
and V
DD33USB_MAX
(see
Figure 2).
V
DD33USB
supplies both USB OTG_HS and USB OTG_FS transceivers. If only
one USB transceiver is used in the application, the GPIOs associated to the other
USB transceiver are still supplied by V
DD33USB
.
If no USB interface is used (USB OTG_HS/OTG_FS), the associated GPIOs
powered by V
DD33USB
operate in V
DD
range (between V
DD_MIN
and V
DD_MAX
).
In the above two configurations, an external capacitor must be connected to
VDD33USB.
• When neither VDD33USB nor VDD50USB is ava
ilable, VDD pins are use to supply
USB transceivers and must be in the range of 3.0 to 3.6 V for the transceiver to operate
correctly
.
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