MIC2774L データシートの表示（PDF） - Micrel

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MIC2774L

Dual Micro-Power Low Voltage Supervisor

Micrel 

Micrel, Inc.

the resistors, simply reduce the value of RTOTAL to

minimize offset errors.

MIC2774

Transient Response

The MIC2774 is inherently immune to very short

negative-going glitches. Very brief transients may exceed

the voltage thresholds without tripping the output.

In general, as shown in Figure 3 and Figure 4, the

narrower the transient, the deeper the threshold overdrive

that the MIC2774 will ignore. The graphs represent the

typical allowable transient duration for a given amount of

threshold overdrive that will not generate a reset.

Figure 1. MIC2774 Example Design

Interfacing to Processors with Bidirectional Reset

Pins

Some microprocessors have reset signal pins that are

bidirectional, rather than input-only. The Motorola

68HC11 family is one example. Because the MIC2774N’s

output is open-drain, it can be connected directly to the

processor’s reset pin using only the pull-up resistor

normally required. See Figure 2.

Figure 3. Typical Input Transient Response

Figure 2. Interfacing to Bidirectional Reset Pin

Figure 4. Typical VDD Transient Response

Ensuring Proper Operation at Low Supply

At VDD levels below 1.2V, the MIC2774’s reset output

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

/RST. In this situation, 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 MIC2774L 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 resistor to the /RST output. A value of 100kΩ is

recommended because this is usually an acceptable

compromise of quiescent current and pull-down current.

The resistor’s value is not critical, however. See Figure 5.

March 16, 2015

8

Revision 2.0

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