MIC2777-29BM5 Ver la hoja de datos (PDF) - Micrel

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MIC2777-29BM5

Dual Micro-Power Low Voltage Supervisor

Micrel 

MIC2777

VCORE

1.0V 5%

VI/O

2.5V 5%

R1

676k

1%

R2

324k

1%

MIC2777-23

VDD /RST

IN

RST

GND

MICROPROCESSOR

VCORE

VI/O

/RESET GND

Figure 1. MIC2777 Example Design

Transient response

The MIC2777 is inherently immune to very short negative-

going “glitches.” Very brief transients may exceed the voltage

thresholds without tripping the output.

As shown in Figure 2a and 2b, in general the narrower the

transient, the deeper the threshold overdrive that will be

ignored by the MIC2777. The graph represents the typical

allowable transient duration for a given amount of threshold

overdrive that will not generate a reset.

Typical INPUT

Transient Response

40

35

30

25

20

15

10

5

0

0

100

200

300

RESET COMP. OVERDRIVE, VREF–VIN(mV)

Figure 2a. Typical INPUT Transient Response

Typical VDD

100 Transient Response

80

60

40

20

00

500 1000 1500 2000

RESET COMP. OVERDRIVE, VREF–VDD(mV)

Figure 2b. Typical VDD Transient Response

Micrel, Inc.

Ensuring Proper Operation at Low Supply

At levels of VDD below 1.2V, the MIC2777’s /RST output

cannot turn on sufficiently to produce a valid logic-low on

/RST. In this situation, other circuits driven by /RST could

be allowed to float, causing undesired operation. (In most

cases, however, it is expected that the circuits driven by the

MIC2777 will be similarly inoperative at VDD ≤ 1.2V.)

If a given application requires that /RST be valid below VDD

= 1.2V, this can be accomplished by adding a pull-down re-

sistor to the /RST output. A value of 100kΩ is recommended

as this is usually an acceptable compromise of quiescent

current and pull-down current. The resistor’s value is not

critical, however. See Figure 3.

The statements above also apply to the MIC2777’s RST out-

put. That is, to ensure valid RST signal levels at VDD<1.2V,

a pull-up resistor (as opposed to a pull-down) should be

added to the RST output. A value of 100kΩ is typical for this

application as well. See Figure 4.

VCC

MICROPROCESSOR

VCC

MIC2777-XX

R1

VDD /RST

/RESET GND

IN

R2

RST

100k

Rpull-down

GND

Figure 3. MIC2777 Valid /RST Below 1.2V

VCC

MICROPROCESSOR

VCC

100k

R1

MIC2777-XX

VDD RST

Rpull-up

RESET GND

IN

R2

/RST

GND

Figure 4. MIC2777 Valid RST Below 1.2V

November 2005

7

MIC2777

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