MAX793 Maxim, MAX793 Datasheet - Page 19

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

have without causing a reset pulse to be issued. As
the amplitude of the transient increases (i.e., goes far-
ther below the reset threshold), the maximum allowable
pulse width decreases. Typically, a V
goes 40mV below the reset threshold and lasts for
10µs or less will not cause a reset pulse to be issued.
A 0.1µF bypass capacitor mounted close to the V
pin provides additional transient immunity.
There is a way to help the watchdog timer monitor soft-
ware execution more closely, which involves setting
and resetting the watchdog input at different points in
the program rather than “pulsing” the watchdog input
high-low-high or low-high-low. This technique avoids a
“stuck” loop, in which the watchdog timer would con-
tinue to be reset within the loop, keeping the watchdog
from timing out. Figure 19 shows an example of a flow
diagram where the I/O driving the watchdog input is
set high at the beginning of the program, set low at the
beginning of every subroutine or loop, then set high
again when the program returns to the beginning. If
the program should “hang” in any subroutine, the prob-
lem would quickly be corrected, since the I/O is contin-
ually set low and the watchdog timer is allowed to time
out, causing a reset or interrupt to be issued.
* The MAX793/MAX795 offer a choice of reset threshold voltage.
Select the letter corresponding to the desired reset threshold volt-
age range (T = 3.00V to 3.15V, S = 2.85V to 3.00V, R = 2.55V
to 2.70V) and insert it into the blank to complete the part number.
The MAX794’s reset threshold is adjustable.
_Ordering Information (continued)
MAX794CPE
MAX794CSE
MAX794EPE
MAX794ESE
MAX795_CPA
MAX795_CSA
MAX795_EPA
MAX795_ESA
PART*
Watchdog Software Considerations
______________________________________________________________________________________
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
TEMP. RANGE
0°C to +70°C
0°C to +70°C
0°C to +70°C
0°C to +70°C
3.0V/3.3V Adjustable Microprocessor
CC
16 Plastic DIP
16 Narrow SO
16 Plastic DIP
16 Narrow SO
PIN-PACKAGE
8 Plastic DIP
8 SO
8 Plastic DIP
8 SO
transient that
CC
TRANSISTOR COUNT: 1271
___________________Chip Information
_________________Pin Configurations
TOP VIEW
( ) ARE FOR MAX794
(RESET IN) BATT OK
Supervisory Circuits
BATT ON
BATT ON
GND
OUT
PFO
GND
V
OUT
V
PFI
MR
CC
CC
1
2
3
4
5
6
7
8
1
2
3
4
DIP / Narrow SO
MAX793
MAX794
DIP/SO
MAX795
16
15
14
13
12
11
10
9
8
7
6
5
RESET
CE OUT
CE IN
BATT
RESET
LOWLINE
RESET
CE OUT
CE IN
WDI
WDO
BATT
19