Datasheet

DS1831/A/B
9 of 14
NON-MASKABLE INTERRUPT CIRCUIT EXAMPLE Figure 9
Example: V
SENSE1
= 11.50V trip point V
SENSE1
=
R2
R2R1
+
X 1.25V
Therefore: 11.50V =
k 100
k 100R1 +
X 1.25V
Resulting In: R1 = 820kW
Repeat the same steps to solve for R3 and R4 with V
SENSE2
.
OPERATION - WATCHDOG TIMER
The watchdog timer function (DS1831A only) forces the WDS signal active (low) when the ST input
does not have a transition (high-to-low or low-to-high) within the predetermined time period. The time-
out period is determined by the condition of the TD
WD
pin (see Table 1). If TD
WD
is connected to ground
the minimum watchdog time-out would be 10ms, TD floating would yield a minimum time-out of 100ms,
and TD
WD
connected to V
CC
would provide a time-out of 1000ms minimum. Time-out of the watchdog
starts when at least one of the RST outputs becomes inactive (high). If a transition occurs on the ST input
pin prior to time-out, the watchdog timer is reset and begins to time-out again. If the watchdog timer is
allowed to time-out, then the WDS output is pulsed active for a minimum of 100µs.
The
WDS output is an open-drain output and must be pulled up externally. In most applications this
output would be connected to one of the Pushbutton inputs and would not require an external pull-up
resistor. The value of the resistors is not critical in most cases but must be set low enough to pull the
output to a high state. A common value used is 10kW. If a
WDS output is connected to a pushbutton input
an additional pull-up resistor can be used (to improve speed of transitions) but is not required.
R1
DS1831
GND
IN1
V
SENSE1
R2
IN2
R3
V
SENSE2
R4
V
CC
10 KW
PBRST
5V
PBRST
3.3V
NMI1
NMI2
MPBRST
W
W