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

applications, 100k

Ω 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:

voltage will trip PFO.

A good rule of thumb for selecting the resistors is to

choose R2 between 250k

Ω 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-

Also, ensure that the voltage at PFI remains above

GND.

Interfacing to µPs with

Bidirectional Reset Pins

6-Pin µP Reset Circuit with

Power-Fail Comparator

_______________________________________________________________________________________

7

R1

R2

V+

GND

( ) ARE FOR MAX6344 ONLY.

TO

µP

PFI

MR

PFO

RESET

(RESET)

MAX6342

MAX6343

MAX6344

Figure 7. Monitoring Two Supplies

R1

R1

R2

R2

V-

GND

( ) ARE FOR MAX6344 ONLY.

100k

Ω

100k

Ω

PFI

MR

PFO

RESET

(RESET)

MAX6342

MAX6343

MAX6344

Figure 8. Monitoring a Negative Voltage

GND

BUFFERED RESET TO

OTHER SYSTEM

COMPONENTS

4.7k

Ω

RESET

MAX6342

MAX6345

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