MIC803-40D3VM3 データシートの表示（PDF） - Micrel

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MIC803-40D3VM3

3-Pin Microprocessor Supervisor Circuit with Open-Drain Reset Output

Micrel 

Micrel, Inc.

Application Information

Microprocessor Reset

The /RESET pin is asserted whenever VCC falls below the

reset threshold voltage, VTH. The /RESET pin remains

asserted for the duration of the reset timeout period

(tRESET) after VCC has risen above the reset threshold

voltage. The reset function ensures the microprocessor is

properly reset and powers up in a known condition after a

power failure. /RESET will remain valid with VCC as low

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

VCC to the MIC803. As shown in Figure 1, it is possible,

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.

MIC803

/RESET Valid at Low Voltage

As VCC drops to 0V, the MIC803 will no longer be able to

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.

+3.3V

VCC

100k

MIC803

RESET

GND

+5V

VCC

µP

RESET

GND

Figure 1. MIC803 Used in a Multiple Supply System

Figure 2. /RESET at Falling VCC

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.

VCC Transients

The MIC803 is relatively immune to negative-going VCC

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

voltage and the minimum point of the VCC glitch.

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

less will not cause a reset. If additional transient immunity

is needed, a 0.1μF bypass capacitor can be placed as

close as possible to the MIC803 on the VCC pin.

August 3, 2015

Figure 3. VCC Threshold

9

Revision 1.2

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