Low-Cost, µP Supervisory Circuits
MAX705–MAX708/MAX813L
+12V
+5V
TO
µP
1M
1%
V
CC
RESET
MAX70_
RESET
R1
130k
1%
PFI
MAX70_
MR
PFO
GND
PARAMETER
MIN
TYP
MAX
UNIT
V
+12V Reset
10.67 10.87 11.50
Threshold at +25°C
Figure 5. RESET Valid to Ground Circuit
Figure 6. Monitoring Both +5V and +12V
+5V
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
V
CC
R1
MR
100k
MAX70_
PFI
PFO
100k
2N3904
V
CC
V
CC
MAX70_
R2
GND
RESET
TO
µP
RESET
4.7k
RESET
µP
V-
+5V
MR
0V
+5V
PFO
0V
V-
5
−
1.25
R1
V
TRIP
GND
GND
Figure 8. Interfacing to µPs with Bidirectional Reset I/O
0V
=
1.25
−
VTRIP
R2
, VTRIP
<
0
Interfacing to µPs with
Bidirectional Reset Pins
µPs with bidirectional reset pins, such as the Motorola
68HC11 series, can contend with the MAX705-MAX708
RESET output. If, for example, the RESET output is driven
high and the µP wants to pull it low, indeterminate logic
levels may result. To correct this, connect a 4.7kΩ
resistor between the RESET output and the µP reset I/O,
as in Figure 8. Buffer the RESET output to other system
components.
Figure 7. Monitoring a Negative Voltage
8
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