MIC2775
Micrel, Inc.
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.
As shown in Figure 3, in general 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.
Typical V
100
80
60
Application Information
Ensuring Proper Operation at Low Supply
At levels of V
DD
below 1.2V, the MIC2775’s /RST output can-
not 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 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 1.
V
CC
MICROPROCESSOR
VCC
Transient Response
DD
40
20
MIC2775-XX
VDD /RST
RST
/MR
Manual
Reset
GND
100k
/RESET GND
0
0
500
1000
1500
2000
RESET COMP. OVERDRIVE, V
REF
–V
DD
(mV)
Figure 3. Typical V
DD
Transient Response
Figure 1. MIC2775 Valid /Reset Below 1.2V
The statements above also apply to the MIC2775’s RST
output. That is, to ensure valid RST signal levels at V
DD
<
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 2.
V
CC
MIC2775-XX
VDD /RST
RST
/MR
GND
MICROPROCESSOR
VCC
/RESET GND
100k
Rpull-down
Manual
Reset
Figure 2. MIC2775 Valid Reset Below 1.2V
MIC2775
6
November 2005
MICREL [ MICREL SEMICONDUCTOR ]
