Micrel, Inc.

MIC2774

March 16, 2015

8

Revision 2.0

minimize offset errors.

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 2. Interfacing to Bidirectional Reset Pin

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 3. Typical Input Transient Response

Ensuring Proper Operation at Low Supply

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

≤ 1.2V.

If a given application requires that /RST be valid below

down resistor to the /RST output. A value of 100k

Ω 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.