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MIC1832

µP Supervisory Circuit

Micrel 

MIC1832

Applications Information

Power Monitor

The /RST and RST pins are asserted whenever VCC falls

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%

tolerance can be selected by connecting the TOL pin to VCC.

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

after VCC has risen above the reset threshold voltage. The

reset function ensures the microprocessor is properly reset

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

/RST will remain valid with VCC as low as 1.4V.

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

Micrel, Inc.

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.

Block Diagram

VCC (8)

TOL (3)

PBRST (1)

ST (7)

TD (2)

TRIP POINT

SELECT

+

-

REF

MANUAL RESET

DEBOUNCE

TIMEOUT

SELECT

RESET

GENERATOR

WATCHDOG

TIMER

RST (6)

RST (5)

GND (4)

MIC1832

6

January 2006

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