Datasheet
Note that this method does not work with the open-drain
output of the MAX6343. The resistor value used is not
critical, but it must be large enough not to load the reset
output when V
CC
is above the reset threshold. For most
applications, 100kΩ is adequate.
Monitoring Two Supplies
Monitor another voltage by connecting a resistor-divider
to PFI as shown in Figure 7. The threshold voltage will
then be given by:
V
TH(PFI)
= 1.25[(R1 + R2) / R2]
where V
TH(PFI)
is the threshold at which the monitored
voltage will trip PFO.
A good rule of thumb for selecting the resistors is to
choose R2 between 250kΩ and 500kΩ and solve for R1.
Connect PFO to MR in applications that require reset to
assert when the second voltage falls below its threshold.
Monitoring a Negative Voltage
Connect the circuit as shown in Figure 8 to use the
power-fail comparator to monitor a negative supply rail.
PFO stays low when V- is good. When V- rises to cause
PFI to be above +1.25V, PFO goes high. By adding the
resistors and transistor as shown, a high PFO triggers
reset. As long as PFO remains high, the MAX6342/
MAX6343/MAX6344 will keep reset asserted. Note that
the accuracy of this circuit depends on the PFI thresh-
old tolerance, the V
CC
line voltage, and the resistors.
Also, ensure that the voltage at PFI remains above
GND.
Interfacing to µPs with
Bidirectional Reset Pins
MAX6342–MAX6345
6-Pin µP Reset Circuit with
Power-Fail Comparator
_______________________________________________________________________________________ 7
V
CC
V
CC
R1
R2
V+
GND
( ) ARE FOR MAX6344 ONLY.
TO µP
PFI MR
PFO
RESET
(RESET)
MAX6342
MAX6343
MAX6344
Figure 7. Monitoring Two Supplies
V
CC
V
CC
R1
R1 R2
R2
V-
GND
( ) ARE FOR MAX6344 ONLY.
V
CC
- 1.25V = 1.25V - V
TRIP
100kΩ
100kΩ
PFI
MR
PFO
RESET
(RESET)
MAX6342
MAX6343
MAX6344
V
TRIP
< 0
Figure 8. Monitoring a Negative Voltage
V
CC
GND
BUFFERED RESET TO
OTHER SYSTEM
COMPONENTS
4.7kΩ
RESET
MAX6342
MAX6345
V
CC
GND
µP
RESET
Figure 9. Interfacing to µPs with Bidirectional Reset I/O
SOT Top Marks
PART
SOT TOP
MARK
PART
SOT TOP
MARK
MAX6342LUT-T AACP MAX6344LUT-T AADQ
MAX6342MUT-T AACQ MAX6344MUT-T AADR
MAX6342TUT-T AACR MAX6344TUT-T AADS
MAX6342SUT-T AACS MAX6344SUT-T AADT
MAX6342RUT-T AACT MAX6344RUT-T AADU
MAX6342ZUT-T AACU MAX6344ZUT-T AADV
MAX6343LUT-T AACV MAX6345LUT-T AADW
MAX6343MUT-T AACW MAX6345MUT-T AADX
MAX6343TUT-T AACX MAX6345TUT-T AADY
MAX6343SUT-T AACY MAX6345SUT-T AADZ
MAX6343RUT-T AACZ MAX6345RUT-T AAEA
MAX6343ZUT-T AADA MAX6345ZUT-T AAEB