DS1831CS datasheet(3/14 Pages) DALLAS

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DS1831C/D/E

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OPERATION – POWER MONITOR

The DS1831 provides the functions of detecting out-of-tolerance conditions on a 3.3 (or 3) volt and

2.5 volt power supply and warning a processor based system of impending power failure. When an input

is detected as out-of-tolerance on either voltage input the RST for that supply will be forced active low.

When that input returns to a valid state the associated RST will remain active for the time delay selected

with the associated TD input and then return to an inactive state until the next input out-of-tolerance

condition.

On power-up both resets are kept active for the selected reset time after the associated power supply input

has reached the selected tolerance. This allows the power supply and system power to stabilize before

RST

is released.

All internal operating current for the DS1831 will be supplied by either the IN3.3V or IN2.5V input which

ever has the highest voltage level.

OPERATION - TOLERANCE SELECT

The DS1831 provides 2 TOL inputs for individual customization of the DS1831 to specific application

requirements. If the TOL for the 2.5 volt supply is tied to the 2.5 volt input a 5% tolerance is selected. If

the TOL is connected to ground a 10% tolerance is selected or if it is left unconnected a 15% tolerance is

selected. If the TOL for the 3.3 volt supply is tied to the 3.3 volt input a 5% tolerance is selected, a 10%

tolerance is selected if it is connected to ground, and a 20% tolerance is selected if the input is left

unconnected. These tolerance conditions are set at power up and can only be changed by power cycling

the device.

OPERATION - RESET TIME-DELAY SELECT

The DS1831 provides 2 TD inputs for individual customization of reset time delays and an additional one

for the DS1831D watchdog. TD inputs select time delays for the IN2.5V and IN3.3V resets outputs and the

Watchdog on the DS1831D. The reset time delays are shown in table 1. These allow the selection of

minimum delays of 10 ms, 100 ms, and 1000 ms.

Wiring an individual reset output to the push-button input of the other voltage reset allows custom reset

timings or allows for the sequencing of the reset outputs. See figure 2.

These time delays are set at power-up and cannot be changed after the device reaches an in-tolerance

condition.

TD INPUTS/RESET AND WATCHDOG TIME-DELAYS Table 1

RESET TIME-DELAY

MIN

TYP

MAX

GND

10 ms

16 ms

20 ms

Float

100 ms

160 ms

200 ms

VCC

1000 ms

1600 ms

2000 ms

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