MIC2775_15 Datasheet, PDF (7/9 Pages) Micrel Semiconductor – Micro-Power Voltage Supervisor

Micrel, Inc.
Application Information
Ensuring Proper Operation at Low Supply
At V_DD levels below 1.2V, the MIC2775’s /RST 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 MIC2775 will be similarly inoperative at V_DD ≤ 1.2V.
If a given application requires that /RST be valid below
V_DD = 1.2V, this can be accomplished by adding a pull-
down resistor to the /RST output. A value or 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 1.
MIC2775
Transient Response
The MIC2775 is inherently immune to very short
negative-going glitches. Very brief transients may exceed
the voltage threshold without tripping the output.
In general, as shown in Figure 3, the narrower the
transient, the deeper the threshold overdrive that will be
ignored by the MIC2775. The graph represents the
typical allowable transient duration for a given amount of
threshold overdrive that will not generate a reset.
Figure 1. MIC2775 Valid /RST Below 1.2V
The statements above also apply to the MIC2775’s RST
output. That is, to ensure valid RST signal levels when
V_DD < 1.2V, a pull-up resistor (as opposed to a pull-down)
should be added to the RST output. A value or 100kΩ is
typical for this application, as well. See Figure 2.
Figure 3. Typical VDD Transient Response
Figure 2. MIC2775 Valid RST Below 1.2V
March 23, 2015
7
Revision 4.0