MAX6302 Maxim, MAX6302 Datasheet - Page 8

• Manufacturer Part Number: MAX6302
• Description: +5V / Low-Power uP Supervisory Circuits with Adjustable Reset/Watchdog
• Manufacturer: Maxim

The reset timeout period is adjustable to accommodate
a variety of µP applications. Adjust the reset timeout
period (t
(C
the reset timeout capacitor as follows:
with C
age (<10nA) type capacitor. Ceramic is recommended.
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
(Figure 3). For normal-mode operation, calculate the
watchdog timeout capacitor as follows:
where C
low leakage (<10nA) type capacitor. Ceramic is recom-
mended.
The Typical Operating Circuit monitors V
monitoring other voltages is simple, and Figure 4 shows
a circuit that accomplishes this. Calculate V
shown in the Reset Threshold section.
+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog
Figure 4. Monitoring a Voltage Other than V
8
__________Applications Information
SRT
_______________________________________________________________________________________
) between SRT and ground (Figure 3). Calculate
SRT
SWT
RS
Monitoring Voltages Other than V
R1
R2
in pF and t
) by connecting a specific value capacitor
V
is in pF and t
IN
Watchdog Timeout Capacitor
RESET IN
C
C
SWT
SRT
RP
MAX6301
MAX6302
MAX6303
MAX6304
SWT
in µs. C
Selecting the Reset and
= t
= t
) between SWT and ground
WD
WD
RP
WD
V
CC
) by connecting a specif-
is in µs. C
⁄ 2.67
⁄ 2.67
SRT
V
CC
V
must be a low-leak-
RST
CC
0.1µF
= 1.22
SRT
CC
(
R1 + R2
. However,
must be a
R2
RST
)
CC
as
In some applications, it is advantageous to put a µP
into sleep mode, periodically “wake it up” to perform
checks and/or tasks, then put it back into sleep mode.
The MAX6301 family supervisors can easily accommo-
date this technique. Figure 5 illustrates an example
using the MAX6302 and an 80C51.
In Figure 5, just before the µC puts itself into sleep
mode, it pulls WDS high. The µC’s I/O pins maintain
their logic levels while in sleep mode and WDS remains
high. This places the MAX6302 in extended mode,
increasing the watchdog timeout 500 times. When the
watchdog timeout period ends, a reset is applied on
the 80C51, “waking it up” to perform tasks. While the µP
is performing tasks, the 80C51 pulls WDS low (select-
ing normal mode), and the MAX6302 monitors the µP
for hang-ups. When the µP finishes its tasks, it puts
itself back into sleep mode, drives WDS high, and
starts the cycle over again. This is a power-saving tech-
nique, since the µP is operating only part of the time
and the MAX6302 has very low quiescent current.
A manual reset option can easily be implemented by
connecting a normally open momentary switch in paral-
lel with R2 (Figure 6). When the switch is closed, the
voltage on RESET IN goes to zero, initiating a reset.
When the switch is released, reset remains asserted for
the reset timeout period and then is cleared. The push-
button switch is effectively debounced by the reset
timer.
Figure 5. Wake-Up Timer
* THREE-STATE LEAKAGE MUST BE <10µA.
MAX6302
GND
Adding a Manual Reset Function
RESET
WDS
WDI
V
CC
V
CC
*
Wake-Up Timer
RST
I/O
I/O
I/O
80C51
GND
V
CC
V
CC