MAX793RCSE データシートの表示（PDF） - Maxim Integrated
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MAX793RCSE Datasheet PDF : 20 Pages
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3.0V/3.3V Adjustable Microprocessor
Supervisory Circuits
VIN
R1
R2
PFI
R3
VCC
MAX793
MAX794
C1*
PFO
GND
TO µP
*OPTIONAL
VIN
R1
R2
PFI
R3
VCC
MAX793
MAX794
C1*
PFO
GND
TO µP
*OPTIONAL
PFO
0V
0V
VL
VH
VIN
VTRIP
( ) VTRIP = VPFT
R1 + R2
R2
WHERE VPFT = 1.237V
( ) VH = (VPFT + VPFH) (R1)
111
++
R1 R2 R3
VPFH = 10mV
( ) VL = R1 VPFT
111
++
– VCC
R1 R2 R3 R3
(a)
PFO
0V
0V
VTRIP
VH
VIN
( ) R1 + R2
VTRIP = VPFT R2
( ) VH = R1 (VPFT + VPFH)
111
++
R1 R2 R3
– VD
R3
WHERE VPFT = 1.237V
VPFH = 10mV
VD = DIODE FORWARD VOLTAGE DROP
(b)
VL = VTRIP
Figure 16. Adding Hysteresis to the Power-Fail Comparator: (a) Symmetrical Hysteresis, (b) Hysteresis Only on Rising VIN
Monitoring an Additional Power Supply
These µP supervisors can monitor either positive or
negative supplies using a resistor voltage divider to
VCC
PFI. PFO can be used to generate an interrupt to the µP
or to cause reset to assert (Figure 12).
Interfacing to µPs with
Bidirectional Reset Pins
Since the RESET output is open drain, the MAX793/
MAX794/MAX795 interface easily with µPs that have
bidirectional reset pins, such as the Motorola 68HC11.
Connecting the RESET output of the µP supervisor
directly to the RESET input of the microcontroller with a
single pullup resistor allows either device to assert
reset (Figure 17).
Negative-Going VCC Transients
These supervisors are relatively immune to short-dura-
tion negative-going VCC transients (glitches) while issu-
ing resets to the µP during power-up, power-down, and
brownout conditions. Therefore, resetting the µP when
VCC experiences only small glitches is usually not rec-
ommended.
VCC
RESET
GENERATOR
RESET
N
MAX793
MAX794
MAX795
GND
VCC
RESET
µP
GND
Figure 17. Interfacing to µPs with Bidirectional Reset I/O
______________________________________________________________________________________ 17
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