3-Pin, Low-Power
碌P Reset Circuits
Ensuring a Valid Reset Output
Down to V
CC
= 0
When V
CC
falls below 1V and approaches the minimum
operating voltage of 0.7V, push/pull-structured reset
sinking (or sourcing) capabilities decrease drastically.
High-impedance CMOS-logic inputs connected to the
RESET
pin can drift to indeterminate voltages. This
does not present a problem in most cases, since most
碌Ps and circuitry do not operate when V
CC
drops
below 1V. For the MAX6801 application, where
RESET
must be valid down to 0, adding a pulldown resistor
between
RESET
and GND removes stray leakage cur-
rents, holding
RESET
low (Figure 2a). The pulldown
resistor value is not critical; 100k鈩?is large enough not
to load
RESET
and small enough to pull it low. For the
MAX6800 application, where RESET must be valid to
V
CC
= 0, a 100k鈩?pullup resistor between RESET and
V
CC
will hold RESET high when V
CC
falls below 0.7V
(Figure 2b).
Since the MAX6802 has an open-drain, active-low out-
put, it typically uses a pullup resistor. With this device,
RESET
will most likely not maintain an active condition,
but will drift to a non-active level due to the pullup
resistor and the reduced sinking capability of the open-
drain device. Therefore, this device is not recommend-
ed for applications where the
RESET
pin is required to
be valid down to V
CC
= 0.
MAX6800/MAX6801/MAX6802
Table 1. Factory-Trimmed Reset Thresholds
RESET
THRESHOLD
SUFFIX
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
T
A
= +25擄C
MIN
4.714
4.615
4.547
4.419
4.301
4.223
4.124
4.026
3.928
4.830
3.732
3.633
3.535
3.437
3.339
3.241
3.142
3.025
2.946
2.877
2.750
2.651
2.583
TYP (V
TH
)
4.80
4.70
4.63
4.50
4.38
4.30
4.20
4.10
4.00
3.90
3.80
3.70
3.60
3.50
3.40
3.30
3.20
3.08
3.00
2.93
2.80
2.70
2.63
MAX
4.886
4.785
4.713
4.581
4.459
4.377
4.276
4.174
4.072
3.970
3.868
3.767
3.665
3.563
3.461
3.359
3.258
3.135
3.054
2.983
2.850
2.749
2.677
T
A
= -40擄C to +125擄C
MIN
4.656
4.559
4.491
4.365
4.249
4.171
4.074
3.977
3.880
3.783
3.686
3.589
3.492
3.395
3.298
3.201
3.104
2.988
2.910
2.842
2.716
2.619
2.551
MAX
4.944
4.841
4.769
4.635
4.511
4.429
4.326
4.223
4.120
4.017
3.914
3.811
3.708
3.605
3.502
3.399
3.296
3.172
3.090
3.018
2.884
2.781
2.709
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