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IN1232 MICROMONITOR CHIP
DESCRIPTION The IN1232 MicroMonitor Chip monitors three vital conditions for a microprocessor: power supply, software execution, and external override. First, a precision temperature-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. The second function the IN1232 performs is pushbutton reset control. The IN1232 debounces the pushbutton input and guarantees an active reset pulse width of 250 ms minimum. The third function is a watchdog timer. The IN1232 has an internal timer that forces the reset signals to the active state if the strobe input is not driven low prior to time-out. The watchdog timer function can be set to operate on time-out settings of approximately 150 ms, 600 ms, and 1.2 seconds. 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 5% or 10% microprocessor power supply monitoring Eliminates the need for discrete components
Dip-8
PBRST TD TOL GND RST RST
V
ST CC NC
SO-14 PIN DESCRIPTION Pushbutton Reset Input Time Delay Set Selects 5% or 10% VCC Detect Ground Reset Output (Active High) Reset Output (Active Low, open drain) Strobe Input +5 Volt Power No Connections
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IN1232
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 0oC to 70oC Operating Temperature (Industrial -40oC to +85oC Version) Storage Temperature -55oC to +125oC Soldering Temperature 260oC 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 (0oC to 70oC)
PARAMETER Supply Voltage ST and PBRST Input High Level ST and PBRST Input Low Level SYMBOL MIN VCC 4.5 VIH 2.0 VIL -0.3 TYP 5.0 MAX 5.5 VCC+0.3 +0.8 UNITS V V V
C; V
NOTES 1 1 1
DC ELECTRICAL CHARACTERISTICS
(0 C to 70
CC = 4.5 to 5.5V)
NOTES 3 5
PARAMETER SYMBOL MIN TYP MAX Input Leakage IIL -1.0 +1.0 Output Current @ 2.4V IOH -8 -10 Output Current @ 0.4V IOL 8 10 Low Level @ RST VOL 0.4 VCC-0.5V VCC-0.1V Output Voltage @ -500 A VOH Operating Current ICC 0.5 2.0 VCC Trip Point (TOL = GND) VCCTP 4.50 4.62 4.74 VCC Trip Point (TOL = VCC) VCCTP 4.25 4.37 4.49 CAPACITANCE PARAMETER SYMBOL MIN TYP MAX Input Capacitance CIN 5 Output Capacitance COUT 7 o oC; V AC ELECTRICAL CHARACTERISTICS (0 C to 70 CC = 5V + 10%) PARAMETER SYMBOL MIN TYP MAX PBRST = VIL tPB 20 RESET Active Time tRST 250 610 1000 ST Pulse Width tST 20 VCC Fail Detect to RST and tRPD 100 175 RST VCC Slew Rate 4.75V to tF 300 4.25V VCC Detect to RST and RST tRPU 250 610 1000 Transition VCC Slew Rate 4.25V to tR 0 5 4.75V PBRST Stable Low to RST tPDLY 20 and RST
UNITS A mA mA V V mA V V
1 1,7 2 1 1 ( tA = 25oC) UNITS NOTES pF pF NOTES 6, 8
UNITS ms ms ns s s ms s ms
4
NOTES: 1. All voltages referenced to ground. 2. Measured with outputs open. 3. PBRST is internally pulled up to VCC with an internal impedance of 10K typical. 4. tR = 5 s.
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IN1232
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. Watchdog can not be disabled. It must be strobed to avoid resets.
OPERATION - POWER MONITOR The IN1232 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 (Pin 3), the VCC comparator outputs the signals RST (Pin 5) and RST (Pin 6). 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 active 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 IN1232 provides an input pin for direct connection to a pushbutton (Figure 2). The pushbutton reset input requires an active low signal. Internally, this input is de-bounced 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 A 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 by the TD input to be typically 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 inactive. If a high-to-low 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 RST and RST signals are driven to the active state for 250 ms minimum. The ST input can be derived from microprocessor 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 time-out. To guarantee that the watchdog timer does not time-out, 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 3. MICROMONITOR BLOCK DIAGRAM
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IN1232
PUSHBUTTON RESET
WATCHDOG TIMER
TIMING DIAGRAM: PUSHBUTTON RESET
TIMING DIAGRAM: STROBE INPUT
WATCHDOG TIMEOUTS TD PIN TIME-OUT MIN TYP MAX GND 62.5 ms 150 ms 250 ms Float 250 ms 600 ms 1000 ms V CC 500 ms 1200 ms 2000 ms TIMING DIAGRAM: POWER DOWN
4
IN1232
TIMING DIAGRAM: POWER UP
5
IN1232
6

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