ATtiny45 datasheet(38/196 Pages) ATMEL

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7598H–AVR–07/09

ATtiny25/45/85

Figure 8-4.

External Reset During Operation

8.5

Brown-out Detection

ATtiny25/45/85 has an On-chip Brown-out Detection (BOD) circuit for monitoring the V

CC 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 V

BOT+ =

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

Note:

1. V

BOT 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 V

CC drops to a voltage where correct

operation of the microcontroller is no longer guaranteed.

2. Centered value, not tested.

Notes:

1. This is the limit to which VDD can be lowered without losing RAM data

Table 8-2.

BODLEVEL Fuse Coding(1)

BODLEVEL [2..0] Fuses

Min V

BOT

Typ V

BOT

Max V

BOT

Units

111

BOD Disabled

110

1.7

1.8

2.0

101

2.5

2.7

2.9

100

4.0

4.3

4.6

011

2.3

(2)

010

2.2

(2)

001

1.9

(2)

000

2.0

(2)

Table 8-3.

Brown-out Characteristics

Symbol

Parameter

Min

Typ

Max

Units

RAM

RAM Retention Voltage

(1)

VHYST

Brown-out Detector Hysteresis

tBOD

Min Pulse Width on Brown-out Reset

µs

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