MAX6746 Maxim, MAX6746 Datasheet - Page 10

• Manufacturer Part Number: MAX6746
• Description: UP Reset Circuits with Capacitor-Adjustable Reset/Watchdog Timeout Delay
• Manufacturer: Maxim

µP Reset Circuits with Capacitor-Adjustable
Reset/Watchdog Timeout Delay
The reset timeout period is adjustable to accommodate
a variety of µP applications. Adjust the reset timeout
period (t
SRT and ground. Calculate the reset timeout capacitor
as folllows:
with t
The watchdog timeout period is adjustable to accom-
modate a variety of µP applications. With this feature,
the watchdog timeout can be optimized for software
execution. The programmer can determine how often
the watchdog timer should be serviced. Adjust the
watchdog timeout period (t
ic value capacitor (C
10
Figure
RESET
RESET
RESET
WDI
WDI
WDI
______________________________________________________________________________________
RP
5. MAX6752/MAX6753 Window Watchdog Diagram
in seconds and C
RP
t
WDI
(c) NORMAL OPERATION (NO PULSING, OUTPUT STAYS HIGH)
t
) by connecting a capacitor (C
WD1
< t
WD1
(MAX) < t
(b) SLOW FAULT
(a) FAST FAULT
C
Applications Information
(MIN)
SRT
WDI
t
WDI
= t
SWT
< t
Selecting Reset/Watchdog
> t
WD2
RP
WD2
) between SWT and GND. For
(MIN)
SRT
(MAX)
/ (5.06 x 10
WD
in Farads.
) by connecting a specif-
Timeout Capacitor
6
),
SRT
) between
normal mode operation, calculate the watchdog time-
out capacitor as follows:
with t
For the MAX6752 and MAX6753 windowed watchdog
function, calculate the slow watchdog period, t
follows:
C
capacitor. Ceramic capacitors are recommended.
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, these supervi-
sors are relatively immune to short-duration supply tran-
sients (glitches). The Maximum Transient Duration vs.
Reset Threshold Overdrive graph in the Typical
Operating Characteristics shows this relationship.
The area below the curves of the graph is the region
in which these devices typically do not generate a reset
pulse. This graph was generated using a falling pulse
applied to V
(V
(reset-threshold overdrive). As the magnitude of the tran-
sient increases (farther below the reset threshold), the
maximum allowable pulse width decreases. Typically, a
V
and lasts 50µs or less does not cause a reset pulse to be
issued.
Figure 6. Interfacing to Other Voltage Levels
CC
SRT
TH
) and ending below it by the magnitude indicated
transient that goes 100mV below the reset threshold
RP
and C
in seconds and C
MAX6747
MAX6749
MAX6451
MAX6753
CC
SWT
V
5V
CC
t
, starting above the actual reset threshold
C
WD2
RESET
N
SWT
must be a low-leakage (<10nA) type
GND
= 0.65 x 10
= t
WD
100kΩ
SRT
/(5.06 x 10
in Farads.
Transient Immunity
9
x C
RESET
SWT
6
),
3.3V
GND
V
µP
CC
WD2
as