Atmel STK526, Руководство пользователя, Страница: 10 / 38

Using the STK526
2-10 STK526 rev. B Hardware User Guide
7709B–AVR–05/07
2.2.3 AT90USB82/162 Power Configuration Settings
This section applies to the following part of the power path diagram :
Figure 2-5 . MCU Power Configurations
Once the power source selected, the internal regulator input of the AT90USB82/162
(UVcc) is powered. Firmware has the responsability to enable or disable the regulator.
Ucap is the output pin of the internal regulator (decoupled with a 1µF capacitor), and
Vcc is the main power source of the MCU. Several cases may be required by the user :
Vsource = 5V, Vcc = 5V : in this mode, the configuration switch (see figure above)
must be in position serigraphied “ NOREG ”. The MCU can still run a USB Device
application if it enables the internal regulator that will power the USB pad and macro.
Vsource = 5V, Vcc = 3.3V : in this mode, the configuration switch must be in the
position serigraphied “ INTREG ”. The Vcc pin will be tied to the regulator output, so
that the AT90USB82/162 itself will power itself from its regulator, and the I/O will be
at 3V3 level.
Vsource = 3.3V, Vcc = 3.3V : in this mode all the MCU power inputs are at the 3V3
level. The configuration switch must be in the position “ NOREG ”. In normal operation
it is recommended to tie all the power pins together (UVcc, Vcc, Ucap) and to disable
the regulator. But the board configuration does not allow to tie together all the power
pins, so that the regulator must be enabled by firmware in order to power the USB
pad and macro (that can lead to some extra-consumption).
Table 2-2 . MCU Power Configuration Jumpers
AT90USBxx2
Vsource
)
Internal
3V3 100mA
Regulator
(1) (2)
UVcc
Vcc Ucap
NOREG INTREG
(3V3 REG)
“3V3 REG”
Jumper position
AT90USB16 I/O power supply Comments View
“NOREG” Primary power source
This is the default configuration.
“INTREG” Internal regulator
This configuration is relevant with a
5V primary powered application
requiring I/O level at 3.3V on the
AT90USB82/162.
3V3 REG
NOREG
INTREG
3V3 REG
NOREG
INTREG