Data Sheet

2

Rev. 1.4, 2007-02-19

TLE 4278 G

The watchdog function monitors the microcontroller, including time base failures. In case

of a missing rising edge within a certain pulse repetition time the watchdog output is set

to LOW. Programming of the max. repetition time can be done easily by an external reset

delay capacitor. To prevent a reset in case of missing pulses, the watchdog output WO

is separate from the reset output RO for the TLE 4278. The watchdog output can be

used as an interrupt signal for the microcontroller. In any case it is possible to connect

pin WO and pin RO externally.

When the controller is set to sleep mode or low power mode its current consumption

drops and no watchdog pulses are created. In order to avoid unnecessary wake-up

signals due to missing pulses at pin WI the watchdog feature can be disabled as a

function of the load current. The switch off threshold is set by an external resistor to pin

WADJ. The watchdog function can also be used as a timer, which periodically wakes up

the controller. Therefore the pin WADJ has to be connected to the output Q.

The power on reset feature is necessary for a defined start of the microprocessor when

switching on the application. The reset signal at pin RO goes high after a certain delay

timed

t

delay time is set by the external delay capacitor. An under voltage reset circuit

supervises the output voltage. In case

V

is set to LOW after a short reset reaction time

t

down to an output voltage

V

adjusted by an external voltage divider. This feature is useful with microprocessors

which guarantee a safe operation down to voltages below the internally set reset

threshold of 4.65 V typical.