AT90USB646_14 Datasheet, PDF (56/456 Pages) ATMEL Corporation – USB boot loader programmed by default in the factory

8.8.3
8.8.4
8.8.5
8.8.6
8.8.7
Brown-out detector
If the Brown-out Detector is not needed by the application, this module should be turned off. If
the Brown-out Detector is enabled by the BODLEVEL Fuses, it will be enabled in all sleep
modes, and hence, always consume power. In the deeper sleep modes, this will contribute sig-
nificantly to the total current consumption. Refer to “Brown-out detection” on page 60 for details
on how to configure the Brown-out Detector.
Internal voltage reference
The internal voltage reference will be enabled when needed by the Brown-out Detection, the
Analog Comparator or the ADC. If these modules are disabled as described in the sections
above, the internal voltage reference will be disabled and it will not be consuming power. When
turned on again, the user must allow the reference to start up before the output is used. If the
reference is kept on in sleep mode, the output can be used immediately. Refer to “Internal volt-
age reference” on page 62 for details on the start-up time.
Watchdog timer
If the Watchdog Timer is not needed in the application, the module should be turned off. If the
Watchdog Timer is enabled, it will be enabled in all sleep modes, and hence, always consume
power. In the deeper sleep modes, this will contribute significantly to the total current consump-
tion. Refer to “Interrupts” on page 68 for details on how to configure the Watchdog Timer.
Port pins
When entering a sleep mode, all port pins should be configured to use minimum power. The
most important is then to ensure that no pins drive resistive loads. In sleep modes where both
the I/O clock (clk_I/O) and the ADC clock (clk_ADC) are stopped, the input buffers of the device will
be disabled. This ensures that no power is consumed by the input logic when not needed. In
some cases, the input logic is needed for detecting wake-up conditions, and it will then be
enabled. Refer to the section “Digital input enable and sleep modes” on page 75 for details on
which pins are enabled. If the input buffer is enabled and the input signal is left floating or have
an analog signal level close to V_CC/2, the input buffer will use excessive power.
For analog input pins, the digital input buffer should be disabled at all times. An analog signal
level close to V_CC/2 on an input pin can cause significant current even in active mode. Digital
input buffers can be disabled by writing to the Digital Input Disable Registers (DIDR1 and
DIDR0). Refer to “DIDR1 – Digital Input Disable Register 1” on page 306 and “DIDR0 – Digital
Input Disable Register 0” on page 326 for details.
On-chip debug system
If the On-chip debug system is enabled by the OCDEN Fuse and the chip enters sleep mode,
the main clock source is enabled, and hence, always consumes power. In the deeper sleep
modes, this will contribute significantly to the total current consumption.
There are three alternative ways to disable the OCD system:
• Disable the OCDEN Fuse
• Disable the JTAGEN Fuse
• Write one to the JTD bit in MCUCR
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