AT90USB82 datasheet(49/306 Pages) ATMEL

49 / 306 page

7707E–AVR–11/08

AT90USB82/162

9.5

Brown-out Detection

AT90USB82/162 has an On-chip Brown-out Detection (BOD) circuit for monitoring the VCC level

during operation by comparing it to a fixed trigger level. The trigger level for the BOD can be

selected by the BODLEVEL Fuses. The trigger level has a hysteresis to ensure spike free

Brown-out Detection. The hysteresis on the detection level should be interpreted as VBOT+ =

VBOT + VHYST/2 and VBOT- = VBOT - VHYST/2.

Note:

1. VBOT may be below nominal minimum operating voltage for some devices. For devices where

this is the case, the device is tested down to VCC = VBOT during the production test. This guar-

antees that a Brown-Out Reset will occur before VCC drops to a voltage where correct

operation of the microcontroller is no longer guaranteed. The test is performed using

BODLEVEL = 110 for AT90USB82/162 and BODLEVEL = 101 for AT90USB82/162L.

When the BOD is enabled, and VCC decreases to a value below the trigger level (VBOT- in Figure

9-5), the Brown-out Reset is immediately activated. When VCC increases above the trigger level

(VBOT+ in Figure 9-5), the delay counter starts the MCU after the Time-out period tTOUT has

expired.

The BOD circuit will only detect a drop in VCC if the voltage stays below the trigger level for lon-

ger than tBOD given in Table 9-1.

Table 9-2.

BODLEVEL Fuse Coding(1)

BODLEVEL 2..0 Fuses

Min VBOT

Typ VBOT

Max VBOT

Units

111

BOD Disabled

110

2.5

2.7

2.9

101

2.7

2.9

3.1

100

2.8

3.0

3.2

011

3.3

3.5

3.7

010

3.4

3.6

3.8

001

3.8

4.0

4.2

000

4.1

4.3

4.5

Table 9-3.

Brown-out Characteristics

Symbol

Parameter

Min

Typ

Max

Units

VHYST

Brown-out Detector Hysteresis

tBOD

Min Pulse Width on Brown-out Reset

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