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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 VCC. 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 k ept 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
VCC
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
VCC
ST
RST
RST
DS1832
µ
8-Pin
µ
-SOP (118-mil)
See Mech. Drawings Section
PBRST
TD
TOL
GND
VCC
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 VCC falls below a preset level as defined by TOL, the VCC 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 ex cell ent control si gnals for a mi cropro 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 delay commences as
the pushbutton reset input is released from the low level.
OPERATION - WATCHDOG TIMER
The watchdog timer function forces RST and RST signals acti ve when th e ST input is not clocked within
the predetermined time period. The timeout period is determined b y 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 disabl ed. The watchdog strobe input must be strobed to avoid
a watchdog timeout and reset.
DS1832
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MICROMONITOR BLOCK DI AGRAM Figure 1
PUSHBUTTON RESET Figure 2
TIMING DI AGRAM: PUSHBUTTON RESET Figure 3
DS1832
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WATCHDOG TIMER Figure 4
WATCHDOG TIMEOUTS Table 1 TIMEOUT
TD MIN TYP MAX
GND 62.5 ms 150 ms 250 ms
Float 250 ms 600 ms 1000 ms
VCC 500 ms 1200 ms 2000 ms
TIMING DI AGRAM: STROBE INPUT Figure 5
TIMING DI AGRAM: POWER DOWN Figure 6
DS1832
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TIMING DIAGRAM: POWER-UP Figure 7
RST VALID TO 0 VOLTS VCC Figure 8
OUTPUT VALID CONDITIONS
The RST output uses a push-pull output which can maintain a valid output down to 0.8 volts VCC. To sink
current below 0.8 volts a resistor can be conn ected from RST to Ground (see Fi gure 8). This arrangement
will maintain a valid value on RST during both power-up and power-down but will draw current when
RST is in the high state. A value of about 100 kΩ=should be adequate in most situations. The output with
a resistor pull-down can maintain a valid reset down to VCC equal to 0 volts.
DS1832
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ABSOLUTE MAXIMUM RATINGS*
Voltage on any Pin Relative to Ground -0.5V to +7.0V
Voltage on I/O Relative to Ground -0.5V to VCC +0.5V
Operating Temperature -40°C to +85°C
Storage Temper ature -55°C to +125°C
Soldering Temperature 260°C for 10 seconds
* This is a stress rating only and functional operation of the device at these or any other conditions
above those indicated in the operation sections of this specification is not implied. Exposure to
absolute maximum rating conditions for extended periods of time may affect reliability.
RECOMMENDED DC OPERATING CONDITIONS (-40°C to +85°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Supply Voltage VCC 1.0 5.5 V 1
2.0 1, 3
ST and PBRST Input High Level VIH
VCC
-0.4
VCC+0.3 V
1, 4
ST and PBRST Input Low Level VIL -0.3 0.5 V 1
DC ELECTRICAL CHARACTERISTICS (-40°C to +85°C; VCC=1.2V to 5.5V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
VCC Trip Point (TOL = GND) VCCTP 2.80 2.88 2.97 V 1
VCC Trip Point (TOL = VCC)V
CCTP 2.47 2.55 2.64 V 1
Input Leakage IIL -1.0 +1.0 µA2
Output Current @ 2.4V IOH 350 µA3
Output Current @ 0.4V IOL 10 mA 3
Output Voltage @ -500 uA VOH VCC
-0.3V
VCC
-0.1V
V4
Operating Current ICC 35 µA5
CAPACITANCE (tA=25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Capacitance CIN 5pF
Output Capacitance COUT 7pF
DS1832
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AC ELECTRICAL CHARACTERISTICS (-40°C to +85°C; VCC=1.2V to 5.5V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
PBRST = VIL tPB 20 ms
RESET Active Time tRST 250 610 1000 ms
ST Pulse Width tST 20 ns 6, 7
VCC Detect to RST and RST tRPD 58µs8
VCC Slew Rate tF20 µs
VCC Detect to RST and RST tRPU 250 610 1000 ms 9
VCC Slew Rate tR0ns
PBRST Stable Low to RST and RST tPDLY 20 ms
NOTES:
1. All voltages referenced to ground.
2. PBRST is internally pulled up to VCC with an internal impedance of 40 kΩ=typical.
3. Measured with VCC ≥ 2.7V.
4. Measured with VCC < 2.7V.
5. Measured with outputs open, VCC ≤ 3.6 volts, and all inputs at VCC or Ground.
6. Must not exceed tTD minimum.
7. The Watchdog cannot be disabled it must be strobed to avoid resets.
8. Noise immunity - Pulses < 2 µs at VCCTP minimum will not cause a reset.
9. tR = 5 µs.
MARKING INFORMATION :
8-pin DIP - “DS1832”
8-pin SOIC - “DS1832”
8-pin - µ-SOP - “1832”
