MIC809 datasheet(5/8 Pages) MICREL

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Microprocessor Reset

The RESET pin is asserted whenever VCC falls below

the reset threshold voltage. The reset pin remains

asserted for a period of 240ms 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. RESET

will remain valid with VCC as low as 1.4V.

VCC Transients

The MIC809/MIC810 are relatively immune to negative-

going VCC glitches below the reset threshold. Typically,

a negative-going transient 125mV below the reset

threshold with a duration of 50

µs (25µs for

MIC8__R/S/T) or less will not cause an unwanted reset.

Interfacing to Bidirectional Reset Pins

The MIC809/MIC810 can interface with

µPs with

bidirectional reset pins by connecting a 4.7K

Ω resistor in

series with the MIC809/MIC810 output and the

µP reset

pin.

RESET Valid to 0V

A resistor can be added from the RESET pin to ground

to ensure the RESET output remains low with VCC

down to 0V. A 100K

Ω resistor connected from RESET

to ground is recommended. The size of the resistor

should be large enough to not load the RESET output

and small enough to pull-down any stray leakage

currents.

Circuit Description

Figure 2. Reset Timing Diagram

Figure 3. RESET Valid to VCC = OV

8++

8JDH

4-5-6

8JDH

VCC

RESET

µP

RESET

VCC

MIC809

VCC

100K

MIC809/MIC810 Microprocessor Reset Circuits

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