DS1832 3.3-Volt MicroMonitor Chip www.dalsemi.com FEATURES PIN ASSIGNMENT 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 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 PBRST 1 8 VCC TD 2 7 ST TOL 3 6 RST GND 4 5 RST DS1832S 8-Pin SOIC (150-mil) See Mech. Drawings Section PBRST TD TOL GND 1 2 3 4 8 7 6 5 VCC ST RST RST DS1832µ 8-Pin µ-SOP (118-mil) See Mech. Drawings Section 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 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 kept in the active state for a minimum of 250 ms to allow the power supply and processor to stabilize. 1 of 7 112099 DS1832 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 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 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. 2 of 7 DS1832 MICROMONITOR BLOCK DIAGRAM Figure 1 PUSHBUTTON RESET Figure 2 TIMING DIAGRAM: PUSHBUTTON RESET Figure 3 3 of 7 DS1832 WATCHDOG TIMER Figure 4 WATCHDOG TIMEOUTS Table 1 TIMEOUT TD GND MIN 62.5 ms TYP 150 ms MAX 250 ms Float 250 ms 600 ms 1000 ms VCC 500 ms 1200 ms 2000 ms TIMING DIAGRAM: STROBE INPUT Figure 5 TIMING DIAGRAM: POWER DOWN Figure 6 4 of 7 DS1832 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 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 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. 5 of 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 -40°C to +85°C -55°C to +125°C 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 PARAMETER Supply Voltage ST and PBRST Input High Level SYMBOL VCC MIN 1.0 VIH 2.0 (-40°C to +85°C) TYP MAX 5.5 UNITS V NOTES 1 VCC+0.3 V 1, 3 1, 4 VCC -0.4 ST and PBRST Input Low Level VIL DC ELECTRICAL CHARACTERISTICS -0.3 0.5 V 1 (-40°C to +85°C; VCC=1.2V to 5.5V) PARAMETER VCC Trip Point (TOL = GND) SYMBOL VCCTP MIN 2.80 TYP 2.88 MAX 2.97 UNITS V NOTES 1 VCC Trip Point (TOL = VCC) VCCTP 2.47 2.55 2.64 V 1 Input Leakage IIL -1.0 +1.0 µA 2 Output Current @ 2.4V IOH µA 3 Output Current @ 0.4V IOL 10 mA 3 Output Voltage @ -500 uA VOH VCC -0.3V V 4 Operating Current ICC µA 5 350 VCC -0.1V 35 CAPACITANCE PARAMETER Input Capacitance Output Capacitance (tA=25°C) SYMBOL CIN COUT 6 of 7 MIN TYP MAX 5 UNITS pF 7 pF NOTES DS1832 AC ELECTRICAL CHARACTERISTICS PARAMETER (-40°C to +85°C; VCC=1.2V to 5.5V) MIN 20 TYP MAX = VIL SYMBOL tPB UNITS ms RESET Active Time tRST 250 610 1000 ms Pulse Width tST 20 PBRST ST 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 5 tF 20 tRPU 250 tR 0 8 610 1000 20 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. 8-pin DIP - “DS1832” 8-pin SOIC - “DS1832” 8-pin - µ-SOP - “1832” 7 of 7 6, 7 µs 8 ms ns NOTES: MARKING INFORMATION: ns µs tPDLY 9. tR = 5 µs. NOTES ms 9