September 2008

5

M9999-091608

MIC6315

Micrel

Applications Information

Microprocessor Reset

reset threshold voltage or if /MR (manual reset) is forced

low. The /RESET pin remains asserted for the duration of

threshold or /MR has returned high. The reset function en-

sure the microprocessor is properly reset and powers up in

a known condition after a power failure. /RESET will remain

The /RESET output is a simple open-drain N-channel MOS-

FETstructure.Apull-upresistormustbeusedtopullthis

output up to some voltage. For most applications, this volt-

MIC6315. It is possible, however, to tie this resistor to some

other voltage. This will allow the MIC6315 to monitor one

voltage while level-shifting the /RESET output to some other

voltage. The pull-up voltage must be limited to 6.0V or less

(absolute maximum) to avoid damage to the MIC6315. The

resistor must be small enough to supply current to the inputs

and leakage paths that are driven by the /RESET output.

/RESET Valid at Low Voltage

pullthe/RESEToutputlow.Atthispoint,thepull-upresistor

will pull the output high. The value of the pull-up resistor and

the voltage it is connected to will affect the point at which

this happens.

Wire OR'ing The /RESET Output

Because the RESET output is open-drain, several reset

sources can be wire-ORed, in parallel, to allow resets from

multiple sources.

glitches below the reset threshold.Typically, a negative-going

transient 125mV below the reset threshold with a duration of

20µsorlesswillnotcauseanunwantedreset.Ifadditional

transient immunity is needed, a bypass capacitor can be

placed a close as possible to the MIC6315.

VCC

RESET

5V SYSTEM

RESET

VCC

MIC6315

+5.0V

MR

10k

+3.3V

MIC6315 Used in a Multiple Supply System