MAX6302 Maxim, MAX6302 Datasheet - Page 6

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

The reset output is typically connected to the reset
input of a microprocessor (µP). A µP’s reset input starts
or restarts the µP in a known state. The MAX6301–
MAX6304 µP supervisory circuits provide the reset
logic to prevent code-execution errors during power-
up, power-down, and brownout conditions (see Typical
Operating Circuit ).
For the MAX6301/MAX6303, RESET changes from high
to low whenever the monitored voltage (V
below the reset threshold voltage (V
remains low as long as V
exceeds V
period, then goes high. When a reset is asserted due to
a watchdog timeout condition, RESET stays low for the
reset timeout period. Anytime reset asserts, the watch-
dog timer clears. At the end of the reset timeout period,
RESET goes high and the watchdog timer is restarted
from zero. If the watchdog timeout period is exceeded
again, then RESET goes low again. This cycle contin-
ues unless WDI receives a transition.
On power-up, once V
teed to be a logic low. For information about applica-
tions where V
Ensuring a Valid RESET/RESET Output Down to V
0V (MAX6303/MAX6304) . As V
low. When V
and RESET remains low. When the reset timeout period
ends, RESET goes high.
On power-down, once V
goes low and is guaranteed to be low until V
below 1V. For information about applications where
V
RESET/RESET Output Down to V
MAX6304) .
The MAX6302/MAX6304 active-high RESET output is
the inverse of the MAX6301/MAX6303 active-low
RESET output, and is guaranteed valid for V
These supervisors monitor the voltage on RESET IN.
The MAX6301–MAX6304 have an adjustable reset
threshold voltage (V
voltage divider (Figure 1). Use the following formula to
calculate V
age triggers a reset):
where V
V
+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog
6
_______________Detailed Description
CC
TH
_______________________________________________________________________________________
is the reset input threshold (1.22V). Resistors R1 and
is less than 1V, see the section Ensuring a Valid
RST
RST
RST
IN
is the desired reset threshold voltage and
, RESET remains low for the reset timeout
V
RST
CC
rises above V
(the point at which the monitored volt-
is less than 1V, see the section
RST
CC
V
TH
) set with an external resistor
reaches 1V, RESET is guaran-
IN
Reset Function/Output
IN
R2
R1 R2
goes below V
RST
is below V
CC
, the reset timer starts
rises, RESET remains
Reset Threshold
CC
= 0V (MAX6303/
V
RST
RST
RST
CC
. Once V
CC
IN
). RESET
, RESET
> 1.31V.
) drops
droops
CC
IN
=
R2 can have very high values to minimize current con-
sumption. Set R2 to some conveniently high value (1MΩ,
for example) and calculate R1 based on the desired
reset threshold voltage, using the following formula:
The watchdog circuit monitors the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within t
(user selected), reset asserts. The internal watchdog
timer is cleared by reset, by a transition at WDI (which
can detect pulses as short as 30ns), or by a transition
at WDS. The watchdog timer remains cleared while
reset is asserted; as soon as reset is released, the timer
starts counting (Figure 2).
The MAX6301–MAX6304 feature two modes of watch-
dog timer operation: normal mode and extended mode.
In normal mode (WDS = GND), the watchdog timeout
period is determined by the value of the capacitor con-
nected between SWT and ground (see the section
Selecting the Reset and Watchdog Timeout Capacitor ).
In extended mode (WDS = V
period is multiplied by 500. For example, in the extend-
ed mode, a 1µF capacitor gives a watchdog timeout
period of 22 minutes (see the graph Extended-Mode
Watchdog Timeout Period vs. C
Operating Characteristics ).
In extended mode, the watchdog function can be dis-
abled by leaving WDI unconnected or by three-stating
the driver connected to WDI. In this mode, the watch-
dog input is internally driven low during the watchdog
Figure 1. Calculating the Reset Threshold Voltage (V
R1
R2
V
IN
R1 R2
RESET IN
MAX6301
MAX6302
MAX6303
MAX6304
V
V
V
CC
RST
TH
CC
), the watchdog timeout
1
V
Watchdog Timer
RST
SWT
0.1µF
= 1.22
in the Typical
(
R1 + R2
R2
RST
)
)
WD