1 of 7 111899
FEATURES
Super-low power version of DS1232
50 µA quiescent current
Halts and restarts an out-of-control
microprocessor
Automatically restarts microprocessor after
power failure
Monitors pushbutton for external override
Accurate 5% or 10% microprocessor power
supply monitoring
8-pin DIP, 8-pin SOIC or space saving µ-SOP
package available
Optional 16-pin SOIC package available
Industrial temperature -40°C to +85°C
available, designated N
PIN ASSIGNMENT
PIN DESCRIPTION
PBRST - Pushbutton Reset Input
TD - Time Delay Set
TOL - Selects 5% or 10% VCC Detect
GND - Ground
RST - Reset Output (Active High)
RST - Reset Output (Active Low, open
drain)
ST - Strobe Input
VCC - +5 Volt Power
DESCRIPTION
The DS1232LP/LPS Low Power MicroMonitor Chip monitors three vital conditions for a
microprocessor: power supply, software execution, and ex ternal over-ri de. First, a precision temperatur e-
compensated reference and comparator circuit monitors the status of VCC. When an out-of-tolerance
condition occurs, an internal power-fail signal is generated which forces reset to the 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.
DS1232LP/LPS
Low Power MicroMonitor Chip
www.dalsemi.com
DS1232LP 8-Pin DIP (300-mil)
See Mech. Drawings Section
PBRST
TD
TOL
GND
V
CC
ST
RST
1
2
3
4
8
7
6
5RST
DS1232LPS 16-Pin SOIC (300-mil)
See Mech. Drawings Section
NC
PBRST
NC
TD
NC
TOL
NC
GND
NC
VCC
NC
ST
NC
RST
NC
RST
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
DS1232LP
µ
(118-mil
µ
-SOP)
See Mech. Drawings Section
PBRST
TD
TOL
GND
V
CC
ST
RST
RST
DS1232LPS-2 8-Pin SOIC (150-mil)
See Mech. Drawings Section
PBRST
TD
TOL
GND
VCC
ST
RST
1
2
3
4
8
7
6
5RST
8
7
6
5
1
2
3
4
DS1232LP/LPS
2 of 7
The second function the DS1232LP/LPS performs is pushbutton reset control. The DS1232LP/LPS
debounces the pushbutton input and guarantees an a ctive reset pulse width of 250 ms minimum. The third
function is a watchdog timer. The DS1232LP/LPS has an internal timer that forces the r eset 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, and 1.2 seconds.
OPERATION - POWER MONITOR
The DS1232LP/LPS 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 4.75 volts. When TOL is connected to VCC, the RST and RST
signals become activ e as VCC falls below 4.5 volts. The RST and RST are excellent control signals for a
microprocessor, 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 DS1232LP/LPS provides an input pin for direct connection to a pushbutton (Figure 1). 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 starts as the
pushbutton reset input is released from low level.
OPERATION - WATCHDOG TIMER
The watchdog timer function forces RST and RST signals to the active state when the ST input is not
stimulated for a predetermined time period. The time period is set b y the TD input to be t ypically 150 ms
with TD connected to ground, 600 ms with TD left unconnected, and 1.2 seconds with TD connected to
VCC. The watchdog timer starts timing out from the set time period as soon as RST and RST are inact ive.
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 to the active state for 250 ms minimum. The ST input can be derived from mic roproc essor address
signals, data signals, and/or control signals. When the microprocessor is functioning 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
shown in Table 1. A typical circuit example is shown in Figure 2.
DS1232LP/LPS
3 of 7
MICROMONITOR BLOCK DI AGRAM
PUSHBUTTON RESET Figure 1
WATCHDOG TIMER Figure 2
DS1232LP/LPS
4 of 7
TIMING DI AGRAM: PUSHBUTTON RESET Figure 3
TIMING DI AGRAM: STROBE INPUT Figure 4
WATCHDOG TIME -OUTS Table 1 TIME-OUT
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
DS1232LP/LPS
5 of 7
TIMING DI AGRAM: POWER-DOWN Figure 5
TIMING DIAGRAM: POWER-UP Figure 6
DS1232LP/LPS
6 of 7
ABSOLUTE MAXIMUM RATINGS*
Voltage on VCC Pin Relative to Ground -0.5V to +7.0V
Voltage on I/O Relative to Ground -0.5V to VCC + 0.5V
Operating Temperature 0°C to 70°C
Operating Temperature (Industrial Version) -40°C to +85°C
Storage Temperature -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 (0°C to 70°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Supply Voltage VCC 4.5 5.0 5.5 V 1
ST and PBRST Input High Level VIH 2.0 VCC+0.3 V 1
ST and PBRST Input Low Level VIL -0.3 +0.8 V 1
DC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCC=4.5 to 5.5V)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Leakage IIL -1.0 +1.0 µA3
Output Current @ 2.4V IOH -8 -10 mA 5
Output Current @ 0.4V IOL 10 mA
Low Level @ RST VOL 0.4 V 1
Output Voltage @ -500 uA VOH VCC
-0.5V
VCC
-0.1V
V 1, 7
Output Current (CMOS) ICC1 50 µA2
Operating Current (TTL) ICC2 200 500 µA8
VCC Trip Point (TOL=GND) VCCTP 4.50 4.62 4.74 V 1
VCC Trip Point (TOL=VCC)V
CCTP 4.25 4.37 4.49 V 1
CAPACITANCE (tA=25°C)
PARAMETER SYMBOL MIN TYP MAX UNITS NOTES
Input Capacitance CIN 5pF
Output Capacitance COUT 7pF
DS1232LP/LPS
7 of 7
AC ELECTRICAL CHARACTERISTICS (0°C to 70°C; VCC=5V ± 10%)
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, 9
VCC Fail Detect to RST and RST tRPD 50 175 µs
VCC Slew Rate 4.75V to 4.25V tF300 µs
VCC Detect to RST and RST Inactive tRPU 250 610 1000 ms 4
VCC Slew Rate 4.25V to 4.75V tR0ns
PBRST Stable Low to RST and RST tPDLY 20 ms
NOTES:
1. All voltages referenced to ground.
2. Measured with outputs open and ST and PBRST within 0.5V of supply rails.
3. PBRST is internally pulled up to VCC with an internal impedance of 40k typical.
4. tR = 5 µs.
5. RST is an open-drain output.
6. Must not exceed tTD minimum. See Table 1.
7. RST remains within 0.5V of VCC on power-down until VCC drops below 2.0V. RST remains within
0.5V of GND on power-down until VCC drops below 2.0V.
8. Measured with outputs open and ST and PBRST at TTL levels.
9. Watchdog can not be disabled. It must be strobed to avoid resets.
MARKING INFORMATION:
8-pin DIP - “DS1232L”
16-pin SOIC - “DS1232L”
8-pin SOIC - “DS1232L”
8-pin µ-SOP - “1232”
