Micrel, Inc.
MIC841/842
October 29, 2013
7
Revision 4.1
Using 3.1V for the VIN(LO) threshold allows calculation of
the two remaining resistor values:
VIN(LO) = 3.1V = 1.24V
+
k
344
2
R
M
1
Eq. 4
Where:
R2 = 56k
R1 = 1M
R2 R3
R1 = 600k
The accuracy of the resistors can be chosen based upon
the accuracy required by the system.
VIN
OUT
VIN(LO)
0V
VIN(HI)
OUT
0V
H AND N VERSIONS
L VERSION
VHYSTERISIS
Figure 2. Output Response and Hysteresis
Programming the MIC842 Thresholds
The voltage threshold is calculated using Equation 5:
VIN(LO) = VREF
+
2
R
2
R
1
R
Eq. 5
Where:
VREF = 1.240V
Figure 3. MIC842 Example Circuit
In order to provide the additional criteria needed to solve
for the resistor values, the resistors can be selected such
that they have a given total value, that is, R1 + R2 =
RTOTAL
. A value such as 1MΩ for R
TOTAL is a reasonable
value because it draws minimum current but has no
significant effect on accuracy.
Input Transients
The MIC841/2 is inherently immune to very short
negative-going “glitches.” Very brief transients may
exceed the VIN(LO) threshold without tripping the output.
As shown in
Figure 4, the narrower the transient, the
deeper the threshold overdrive that will be ignored by the
MIC841/2. The graph represents the typical allowable
transient duration for a given amount of threshold
overdrive that will not generate an output.
Figure 4. Input Transient Response