AT90PWM161 datasheet(53/327 Pages) ATMEL

53 / 327 page

7734Q–AVR–02/12

AT90PWM81/161

7.1.5

Brown-out Detection

AT90PWM81/161 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

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

Notes:

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 V

CC drops to a voltage where correct

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

BODLEVEL = 010 for Low Operating Voltageand BODLEVEL = 101 for High Operating

Voltage.

2. Values are guidelines only.

Notes:

1. Values are guidelines only.

When V

CC decreases to a value below the trigger level (VBOT- in Figure 7-5 on page 54), the

Brown-out Reset is immediately activated. When V

CC increases above the trigger level (VBOT+ in

Figure 7-5 on page 54), the delay counter starts the MCU after the Time-out period t

TOUT has

expired.

The BOD circuit will only detect a drop in V

CC if the voltage stays below the trigger level for lon-

ger than t

BOD given in Table 7-3.

Table 7-2.

BODLEVEL fuse coding

(1)(2).

BODLEVEL 2..0 fuses

Min VBOT

Typ VBOT

Max VBOT

Units

111

Forbidden, BOD must be enabled

110

1.8

101 (default configuration)

2.7

100

3.9

4.3

4.6

011

2.3

010

2.2

001

1.9

000

2.5

2.0

2.9

Table 7-3.

Brown-out characteristics (1).

Symbol

Parameter

Minimum

Typical

Maximum

Units

VHYST

Brown-out detector hysteresis

BOD

Minimum pulse width on brown-out reset

µs

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