Micrel, Inc.

MIC803

August 3, 2015

9

Revision 1.2

Application Information

Microprocessor Reset

asserted for the duration of the reset timeout period

voltage. The reset function ensures the microprocessor is

properly reset and powers up in a known condition after a

as 1.0V.

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

MOSFET structure. A pull-up resistor must be used to

pull this output up to some voltage. For most applications,

this voltage will be the same power supply that supplies

however, to tie this resistor to some other voltage. This

will allow the MIC803 to monitor one voltage while level-

shifting the /RESET output to some other voltage. The

pull-up voltage must be limited to 5.5V. The resistor must

be small enough to supply current to the inputs and

leakage paths that are driven by the /RESET output.

100k

+3.3V

RESET

µP

MIC803

GND

GND

RESET

+5V

Figure 1. MIC803 Used in a Multiple Supply System

/RESET Valid at Low Voltage

pull the /RESET output low, and the pull-up resistor 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 ORing the /RESET Output

Since 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

(see

Typical

Characteristics,

graph

titled

“Maximum

Transient

Duration vs. Overdrive”). As shown in Figure 3, the

overdrive voltage is the difference between the threshold

Typically, an overdrive of 100mV, with duration of 15

μs or

less will not cause a reset. If additional transient immunity

is needed, a 0.1

μF bypass capacitor can be placed as

close as possible to the MIC803 on the VCC pin.