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ATA6603

Microcontroller with LIN Transceiver, 5V Regulator and Watchdog

Atmel Corporation 

ATA6602/ATA6603

Figure 3-8. Power Dissipation: Safe Operating Area versus VDD Output Current and Supply

Voltage VS at Different Temperatures Tcase

55

105˚C

50

45

40

125˚C

35

30

25

20

15

10

5

0

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

VS (V)

3.3.17 Watchdog

The watchdog anticipates a trigger signal from the microcontroller at the NTRIG (negative edge)

or the PTRIG (positive edge) input within a period time window of Twd. The trigger signal must

exceed a minimum time ttrigmin > 3 µs. If a triggering signal is not received, a reset signal will be

generated at output NRES. The timing basis of the watchdog is provided by the internal oscilla-

tor, of which the time period Tosc is adjustable via the external resistor Rwd_osc (10 kΩ to 120 kΩ).

In Silent or Sleep Mode, the watchdog is switched off to reduce current consumption.

Minimum time for first watchdog pulse is required after the undervoltage reset at NRES disap-

pears and is defined as lead time td.

3.3.17.1

Typical Timing Sequence with Rwd_osc = 51 kΩ

The trigger signal Twd is adjustable between 2.9 ms and 33 ms via the external resistor Rwd_osc.

For example, with an external resistor of Rwd_oscSC = 51 kΩ ±1%, the typical parameters of the

watchdog come out as follows:

tOSC = 12.5 µs due to 51 kΩ

td = 3922 × 12.5 µs = 49 ms

t1 = 800 × 12.5 µs = 10 ms

t2 = 840 × 12.5 µs = 10.5 ms

tnres = 157 × 12.5 µs = 1.96 ms

After ramping up the battery voltage VS or wake up from Sleep Mode, the 5V regulator is

switched on. The reset output NRES stays low for the time treset (typically 10 ms), then it

switches to high and the watchdog waits for the watchdog sequence from the microcontroller.

This lead time td follows after the reset and is td = 49 ms. After wake up from Silent Mode the

RXD switches to low. The lead time td follows the negative edge of this RXD signal. In this time,

the first watchdog pulse from the microcontroller is required. If the trigger pulse NTRIG (or

PTRIG, as the case may be) occurs during this time, the time t1 starts immediately. If no trigger

signal occurs during the time td, a watchdog reset with tNRES = 1.96 ms will reset the microcon-

15

4921C–AUTO–01/07

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