Low-Cost, µP Supervisory Circuits
MAX70_
RESET
R1
+12V
+5V
1M
VCC
RESET
1%
MAX70_
MR
130k
1%
PFI
PFO
GND
TO µP
PARAMETER MIN TYP MAX UNIT
+12V Reset
10.67 10.87 11.50 V
Threshold at +25°C
Figure 5. RESET Valid to Ground Circuit
Figure 6. Monitoring Both +5V and +12V
+5V
R1
R2
VCC
MR
MAX70_
100k
PFO
PFI
100k
2N3904
RESET
GND
TO µP
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
VCC
MAX70_
4.7k
RESET
VCC
µP
RESET
V-
+5V
MR
0V
+5V
PFO
0V
V-
VTRIP
0V
5 − 1.25 = 1.25 − VTRIP , VTRIP < 0
R1
R2
Figure 7. Monitoring a Negative Voltage
GND
GND
Figure 8. Interfacing to µPs with Bidirectional Reset I/O
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.
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