5

9145D–AUTO–05/10

ATA5021

The clock frequency determines all time periods of the logical part as shown in Section 7. “Elec-

trical Characteristics” on page 9 under the subheading “Timing”.

3.3

Supply Voltage Monitoring, Pin 5

During ramp-up of the supply voltage and in the case of supply-voltage drops, the integrated

power-on reset (POR) circuitry sets the internal logic to a defined basic status and generates a

reset pulse at the reset output, pin 5. A hysteresis in the POR threshold prevents the circuit from

oscillating. During ramp-up of the supply voltage, the reset output stays active for a specified

period of time (t

on page 5).

3.4

Switch-over Mode Time, Pin 3

The switch-over mode time enables the synchronous operation of microcontroller and watchdog.

When the power-on reset time has elapsed, the watchdog has to be switched to monitoring

mode by the microcontroller by a “low” signal transmitted to the mode pin (pin 3) within the

time-out period, t

watchdog generates a reset pulse, t

chronized with the switch-over mode time, t

Figure 3-1.

Power-on Reset and Switch-over Mode

81.20

0.47

63.47

63.75

1.6%

81.20

1.04

136.32

135.00

1.9%

81.20

4.75

595.56

592.50

0.7%

81.20

10.49

1253.21

1240.00

1.3%

100.00

0.23

40.07

38.88

–2.1%

100.00

0.47

78.07

78.00

1.2%

100.00

1.04

167.76

164.00

–1.7%

100.00

4.75

733.17

730.00

0.9%

100.00

10.49

1542.84

1530.00

0.5%

119.50

0.23

47.81

46.38

–1.7%

119.50

0.47

93.20

93.00

0.8%

119.50

1.04

200.37

200.25

1.1%

119.50

4.75

875.90

870.00

0.5%

119.50

10.49

1843.26

1835.00

0.9%

Table 3-1.

Comparison Table Clock Period Calculation versus Measurement on Test Board

R1 (k

Ω)C1 (nF)

Period “T” (µs) by

New Formula

Period “T” (µs) by

Measurement

Deviation of New

Formula versus

Measurement

Reset out

Mode

Pin 3

Pin 5

Pin 6