MIC1832

Micrel, Inc.

MIC1832

6

January 2006

Applications Information

Power Monitor

below the reset threshold voltage as determined by the TOL

pin. A 5% tolerance level (4.62V reset threshold voltage) can

be selected by connecting the TOL pin to ground and a 10%

The reset pins will remain asserted for a period of 250ms

reset function ensures the microprocessor is properly reset

and powers up into a known condition after a power failure.

Watchdog Timer

The microprocessor can be mounted by connecting the /ST

pin (watchdog input) to a bus line or I/O line. If a high-to-low

does not occur on the/ST pin within the watchdog timeout

Block Diagram

+

-

REF

WATCHDOG

TIMER

VCC (8)

GND (4)

RST (5)

TD (2)

RST (6)

RESET

GENERATOR

ST (7)

TIMEOUT

SELECT

PBRST (1)

MANUAL RESET

DEBOUNCE

TRIP POINT

SELECT

TOL (3)

period (determined by the TD pin, see Table 1.), the /RST and

the RST will remain asserted for 250ms when this occurs. A

minimum pulse of 75ns or any transition high-to-low on the

/ST pin will reset the watchdog timer. The watchdog timer

will be reset if /ST sees a valid transition within the watchdog

timeout period.

Pushbutton Reset Input

The /PBRST input can be driven with a manual pushbutton

switch or with external logic signals. the input is internally

debounced and requires an active low signal to force the

reset outputs into their active states. The /PBRST input will

recognize any pulse that is 20ms in duration or greater and

will ignore all pulses that are less than 1ms in duration.