AT90USB82 datasheet(52/306 Pages) ATMEL

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7707D–AVR–07/08

AT90USB82/162

9.8

Internal Voltage Reference

AT90USB82/162 features an internal bandgap reference. This reference is used for Brown-out

Detection, and it can be used as an input to the Analog Comparator.

9.8.1

Voltage Reference Enable Signals and Start-up Time

The voltage reference has a start-up time that may influence the way it should be used. The

start-up time is given in Table 9-4. To save power, the reference is not always turned on. The

reference is on during the following situations:

When the BOD is enabled (by programming the BODLEVEL [2..0] Fuse).

When the bandgap reference is connected to the Analog Comparator (by setting the

ACBG bit in ACSR).

Thus, when the BOD is not enabled, after setting the ACBG bit, the user must always allow the

reference to start up before the output from the Analog Comparator is used. To reduce power

consumption in Power-down mode, the user can avoid the three conditions above to ensure that

the reference is turned off before entering Power-down mode

9.9

Watchdog Timer

AT90USB82/162 has an Enhanced Watchdog Timer (WDT). The main features are:

• Clocked from separate On-chip Oscillator

• 3 Operating modes

– Interrupt

– System Reset

– Interrupt and System Reset

Table 9-4.

Internal Voltage Reference Characteristics

Symbol

Parameter

Condition

Min

Typ

Max

Units

VBG

Bandgap reference voltage

CC = 2.7V - 5.5V

1.0

1.1

1.2

tBG

Bandgap reference start-up time

µs

IBG

Bandgap reference current

consumption

-10

µA

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