Dallas Semiconductor DS1832U, DS1832S, DS1832 Datasheet

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FEATURES

 Halts and restarts an out-of-control

microprocessor

 Holds microprocessor in check during power

transients

 Automatically restarts microprocessor after

power failure

 Monitors pushbutton for external override
 Accurate 10% or 20% microprocessor power

monitoring

 Eliminates need for discrete components
 20% tolerance for use with 3.0-volt systems
 Pin-compatible with the DS1232
 Low cost 8-pin DIP, 8-pin SOIC, and space

saving µ-SOP packages available

 Industrial temperature range of -40°C to

+85°C

PIN ASSIGNMENT

PIN DESCRIPTION

PBRST - Pushbutton Reset Input

TD - Time Delay Set
TOL - Selects 10% or 20% VCC Detect
GND - Ground
RST - Active High Reset Output

RST - Active Low Reset Output
ST - Strobe Input

VCC - Power Supply

DESCRIPTION

The DS1832 3.3-Volt MicroMonitor monitors three vital conditions for a microprocessor: power supply,
software execution, and external override. First, a precision temperature-compensated reference and
comparator circuit monitor the status of V

CC

. When an out-of-tolerance condition occurs, an internal
power-fail signal is generated which forces the resets to an active state. When VCC returns to an
in-tolerance condition, the reset signals are kept in the active state for a minimum of 250 ms to allow the
power supply and processor to stabilize.

DS1832

3.3-Volt MicroMonitor Chip

www.dalsemi.com

DS1832 8-Pin DIP (300-mil)
See Mech. Drawings Section

PBRST

TD

TOL

GND

V

CC

ST
RST
RST

1
2
3
4

8
7
6
5

DS1832S 8-Pin SOIC (150-mil)

See Mech. Drawings Section

1
2
3

4

8
7
6

5

PBRST

TD

TOL

GND

V

CC

ST
RST
RST

DS1832µ 8-Pin µ-SOP (118-mil)

See Mech. Drawings Section

PBRST

TD

TOL

GND

V

CC

ST
RST
RST

1
2
3
4

8
7
6
5

DS1832

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The second function the DS1832 performs is pushbutton reset control. The DS1832 debounces the
pushbutton input and guarantees an active reset pulse width of 250 ms minimum. The third function is a
watchdog timer. The DS1832 has an internal timer that forces the reset signals to the active state if the
strobe input is not driven low prior to timeout. The watchdog timer function can be set to operate on
timeout settings of approximately 150 ms, 600 ms, or 1.2 seconds.

OPERATION - POWER MONITOR

The DS1832 detects out-of-tolerance power supply conditions and warns a processor-based system of
impending power failure. When V

CC

falls below a preset level as defined by TOL, the V

CC

comparator

outputs the signals RST and

RST . When TOL is connected to ground, the RST and RST signals become

active as VCC falls below 2.98 volts. When TOL is connected to VCC, the RST and RST signals become
active as VCC falls below 2.64 volts. The RST and RST are excellent control signals for a micropro cessor,
as processing is stopped at the last possible moments of valid VCC. On power-up, RST and RST are kept

active for a minimum of 250 ms to allow the power supply and processor to stabilize.

OPERATION - PUSHBUTTON RESET

The DS1832 provides an input pin for direct connection to a pushbutton reset (see Figure 2). The
pushbutton reset input requires an active low signal. Internally, this input is debounced and timed such

that RST and RST signals of at least 250 ms minimum are generated. The 250 ms dela y commences as
the pushbutton reset input is released from the low level.

OPERATION - WATCHDOG TIMER

The watchdog timer function forces RST and RST signals active when the ST input is not clocked within
the predetermined time period. The timeout period is determined by the condition of the TD pin. If TD is
connected to ground the minimum watchdog timeout would be 62.5 ms, TD floating would yield a
minimum timeout of 250 ms, and TD connected to VCC would provide a timeout of 500 ms minimum.

Timeout of the watchdog starts when RST and RST become inactive. If a high-to-low transition occurs
on the ST input pin prior to timeout, the watchdog timer is reset and begins to timeout again. If the
watchdog timer is allowed to timeout, then the RST and RST signals are driven active for a minimum of
250 ms. The

ST input can be derived from many microprocessor outputs. The most typical signals used

are the microprocessor address signals, data signals or control signals. When the microprocessor
functions normally, these signals would, as a matter of routine, cause the watchdog to be reset prior to
timeout. To guarantee that the watchdog timer does not timeout, a high-to-low transition must occur at or
less than the minimum times shown in Table 1. A typical circuit example is shown in Figure 4.

The DS1832 watchdog function cannot be disabled. The watchdog strobe input must be strobed to avoid
a watchdog timeout and reset.

DS1832

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MICROMONITOR BLOCK DIAGRAM Figure 1

PUSHBUTTON RESET Figure 2

TIMING DIAGRAM: PUSHBUTTON RESET Figure 3