DS1832 DS1832 3.3 Volt MicroMonitor Chip FEATURES PIN ASSIGNMENT * Halts and restarts an out-of-control microprocessor * Holds microprocessor in check during power tran- sients * Automatically restarts microprocessor after power PBRST 1 8 VCC TD 2 7 ST TOL 3 6 RST GND 4 5 RST DS1832 8-PIN DIP (300 MIL) See Mech. Drawings Section failure * Monitors pushbutton for external override PBRST * Accurate 10% or 20% microprocessor power monitoring * Eliminates need for discrete components 1 2 8 VCC TD 7 ST TOL 3 6 RST GND 4 5 RST DS1832S 8-PIN SOIC (150 MIL) See Mech. Drawings Section * 20% tolerance for use with 3.0 volt systems PBRST TD TOL GND * Pin compatible with the DS1232 * Low cost 8-pin DIP, 8-pin SOIC, and space saving 1 2 3 4 8 7 6 5 VCC ST RST RST DS1232 8-PIN -SOP (118 MIL) See Mech. Drawings Section -SOP packages available * Industrial temperature range of -40C to +85C PIN DESCRIPTION PBRST TD TOL GND RST RST ST VCC - - - - - - - - Pushbutton Reset Input Time Delay Set Selects 10% or 20% VCC Detect Ground Active High Reset Output Active Low Reset Output Strobe Input 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 monitors 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 kept in the active state for a minimum of 250 ms to allow the power supply and processor to stabilize. 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 time-out. The watchdog timer function can be set to operate on time-out settings of approximately 150 ms, 600 ms, or 1.2 seconds. 062698 1/7 DS1832 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 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 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 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 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 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 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 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. The watchdog timer function forces RST and RST signals active when the ST input is not clocked within the MICROMONITOR BLOCK DIAGRAM Figure 1 VCC ST RST VCC VCC TOLERANCE BIAS TOL + - VCC DIGITAL DELAY T.C. REFERENCE RST PBRST LEVEL SENSE AND DEBOUNCE TD VOLTAGE SENSE 062698 2/7 TIME-OUT COMPARATOR DS1832 PUSHBUTTON RESET Figure 2 SUPPLY VOLTAGE 8051 P VCC PBRST TD ST ALE DS1832 TOL RST GND RST RST TIMING DIAGRAM: PUSHBUTTON RESET Figure 3 tPB PBRST tPDLY VIH VIL tRST RST VOH RST VOL WATCHDOG TIMER Figure 4 SUPPLY VOLTAGE VCC PBRST Z80 ST TD MREQ DS1832 TOL RST RST GND RST DECODER ADDRESS BUS 062698 3/7 DS1832 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 TIMING DIAGRAM: STROBE INPUT Figure 5 INVALID STROBE INDETERMINATE STROBE VALID STROBE ST MIN. MAX. tTD RST TIMING DIAGRAM: POWER DOWN Figure 6 tF VCC VCCTP(MAX) VCCTP VCCTP(MIN) tRPD RST RST SLEWS WITH VCC VOH RST 062698 4/7 VOL DS1832 TIMING DIAGRAM: POWER UP Figure 7 tR VCCTP(MAX) VCCTP VCCTP(MIN) VCC tRPU RST VOH VOL RST RST VALID TO 0 VOLTS VCC Figure 8 RST INPUT 100K 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 connected from RST to Ground (see Figure 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 100K 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. 062698 5/7 DS1832 ABSOLUTE MAXIMUM RATINGS* Voltage on any Pin Relative to Ground Voltage on I/O Relative to Ground Operating Temperature Storage Temperature Soldering Temperature -0.5V to +7.0V -0.5V to VCC +0.5V -40C to +85C -55C to +125C 260C 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. (-40C to +85C) RECOMMENDED DC OPERATING CONDITIONS PARAMETER SYMBOL MIN Supply Voltage VCC ST and PBRST Input High Level VIH TYP MAX UNITS NOTES 1.0 5.5 V 1 2.0 VCC+0.3 V 1, 3 VCC-0.4 ST and PBRST Input Low Level VIL 1, 4 -0.3 0.5 1 (-40C to +85C; VCC=1.2V to 5.5V) DC ELECTRICAL CHARACTERISTICS PARAMETER V 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) VCCTP 2.47 2.55 2.64 V 1 Input Leakage IIL -1.0 +1.0 A 2 Output Current @ 2.4V IOH A 3 Output Current @ 0.4V IOL 10 mA 3 Output Voltage @ -500 uA VOH VCC-0.3V V 4 Operating Current ICC A 5 350 VCC-0.1V 35 (tA = 25C) CAPACITANCE PARAMETER Input Capacitance Output Capacitance 062698 6/7 SYMBOL MIN TYP MAX UNITS CIN 5 pF COUT 7 pF NOTES DS1832 (-40C to +85C; VCC = 1.2V to 5.5V) AC ELECTRICAL CHARACTERISTICS PARAMETER SYMBOL MIN PBRST = VIL tPB 20 RESET Active Time tRST 250 ST Pulse Width tST 20 VCC Detect to RST and RST VCC Slew Rate VCC Detect to RST and RST VCC Slew Rate PBRST Stable Low to RST and RST tRPD TYP MAX 610 1000 20 tRPU 250 tR 0 NOTES ms 5 tF UNITS 8 ms ns 6, 7 s 8 s 610 tPDLY 1000 ms 9 ns 20 ms NOTES: 1. All voltages referenced to ground. 2. PBRST is internally pulled up to VCC with an internal impedance of 40K 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 s at VCCTP minimum will not cause a reset. 9. tR = 5 s. MARKING INFORMATION: 8-pin DIP - "DS1832" 8-pin SOIC - "DS1832" 8-pin - -SOP - "1832" 062698 7/7