September 2001 5 MIC834
MIC834 Micrel
INP
OUTVDD
GND
MIC834
470k
V
IN
R1
R2
V
OUT
4
21
5
Figure 1. Example Circuit
Input Transients
The MIC834 is inherently immune to very short negative-
going “glitches.” Very brief transients may exceed the V
IN(lo)
threshold without tripping the output.
As shown in Figure 2, the narrower the transient, the deeper
the threshold overdrive that will be ignored by the MIC834.
The graph represents the typical allowable transient duration
for a given amount of threshold overdrive that will not gener-
ate an output.
0
20
40
60
80
100
120
140
1 10 100 1000
MAX. TRANSIENT DURATION (µs)
RESET COMP. OVERDRIVE, V
REF
–V
LTH
(mV)
Input Transient
Response
Figure 2. Input Transient Response
Applications Information
Output
Since the MIC834 output is an open-drain MOSFET, most
applications will require a pull-up resistor. The value of the
resistor should not be too large or leakage effects may
dominate. 470kΩ is the maximum recommended value. Note
that the output may be pulled up as high as 6V regardless of
the IC’s supply voltage. See “Electrical Characteristics.”
Programming the Threshold
The voltage threshold is calculated using:
VV
R1 R2
R2
IN(lo) REF
=
+
where:
V 1.240V
REF
=
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 = R
TOTAL
. A
value such as 1MΩ for R
TOTAL
is a reasonable value because
it draws minimum current but has no significant effect on
accuracy.
When working with large resistors, a small amount of leakage
current can cause voltage offsets that degrade system accu-
racy. The maximum recommended total resistance from V
IN
to ground is 3MΩ. The accuracy of the resistors can be
chosen based upon the accuracy required by the system. The
inputs may be subjected to voltages as high as 6V steady-
state without adverse effects of any kind regardless of the
IC’s supply voltage. This applies even if the supply voltage is
zero. This permits the situation in which the IC’s supply is
turned off, but voltage is still present on the inputs. See
“Electrical Characteristics.”
