MAX793 Maxim, MAX793 Datasheet - Page 17

• Manufacturer Part Number: MAX793
• Description: 3.0V/3.3V Adjustable Microprocessor Supervisory Circuits
• Manufacturer: Maxim

Figure 16. Adding Hysteresis to the Power-Fail Comparator: (a) Symmetrical Hysteresis, (b) Hysteresis Only on Rising V
timeout period (because PFI is below the PFI thresh-
old), the IC will test the voltage level on PFO, find that it
is low, and incorrectly decide to enter freshness seal
mode. If V
not be connected to OUT and any devices powered by
OUT will lose power.
Applications that do not use the PFO comparator need
not be affected by this problem. Simply connect PFI to
V
out periods. Freshness seal mode can be entered only
when PFO is low.
The IC is under revision to correct this problem. The
revised IC will disable PFO during all reset timeout peri-
ods including MR-initiated ones. This revision will not
affect applications that either do not use MR or do not
use PFO, but could affect applications that require the
use of the PFO output during MR-initiated reset timeout
periods. The revised ICs are expected to be available
in late 1996. For technical assistance, please contact
Maxim Applications at 1-800-998-8800 or at
http:// www. maxim-ic.com.
CC
(a)
and PFO will be driven high during all reset time-
PFO
R1
R2
V
CC
V
0V
V
TRIP
H
L
V
= (V
= R1 V
0V
IN
= V
is later removed, the backup battery will
PFT
PFT
+ V
PFT
______________________________________________________________________________________
(
R1 + R2
PFH
C1*
(
R2
R1
) (R1)
1
TO P
+
)
1
R2
R3
(
3.0V/3.3V Adjustable Microprocessor
R1
1
+
V
L
+
1
R3
PFI
PFO
1
R2
)
V
TRIP
–
+
V
1
R3
R3
CC
MAX793
MAX794
)
GND
V
WHERE
CC
V
H
V
V
PFT
PFH
*OPTIONAL
= 1.237V
= 10mV
V
IN
(b)
Figure 17. Interfacing to µPs with Bidirectional Reset I/O
V
CC
GENERATOR
Supervisory Circuits
RESET
PFO
V
MAX793
MAX794
MAX795
V
TRIP
WHERE
V
GND
R1
R2
H
0V
CC
= R1 (V
V
= V
0V
IN
PFT
V
V
PFT
PFH
PFT
V
V
(
R1 + R2
D
L
RESET
+ V
= 1.237V
= DIODE FORWARD VOLTAGE DROP
= V
N
= 10mV
R2
C1*
TRIP
PFH
TO P
)
)
(
R1
R3
1
V
+
TRIP
1
R2
PFI
PFO
+
1
R3
RESET
MAX793
MAX794
)
V
GND
–
CC
V
H
V
R3
D
GND
V
CC
P
*OPTIONAL
IN
V
IN
17