DS1814 DALLAS | Alldatasheet
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Technical content
FEATURES
/g167 Halts and restarts an out-of-control microprocessor /g167 Holds microprocessor in check during power transients /g167 Automatically restarts microprocessor after power failure /g167 Monitors pushbutton for external override /g167 Accurate 5%, 10%, or 20% (3V only) microprocessor power monitoring /g167 Eliminates the need for discrete components /g167 20% tolerance for use with 3.0V systems /g167 Pin- and function-compatible with the MAX823/24/25 products /g167 Low cost SOT-23-5 package /g167 Industrial temperature range: -40/g176C to +85/g176C DEVICE RST RST PBRST WD DS181xA DS181xB DS181xC X X X X X X X X X x = "DS1814" for 5V devices x = "DS1819" for 3V devices PIN ASSIGNMENT PIN DESCRIPTION DS181xA
1 RST Active Low Reset Output
2 GND Ground
3 PBRST Pushbutton Reset Input
4 ST Strobe Input
5 VCC Power Supply
3 RST Active High Reset Output
PBRST Pushbutton Reset Input
DESCRIPTION
The DS1814 5-Volt MicroMonitor and the DS1819 3.3V MicroMonitor monitor 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 V CC. When an out-of-tolerance condition occurs, an internal power-fail signal is generated which forces the reset(s) to an active state. When V CC returns to an in-tolerance condition, the reset signal is kept in the active state for a minimum of 140ms to allow the power supply and processor to stabilize. DS1814/DS1819 5V and 3.3V MicroMonitor www.maxim-ic.com 321 SOT-23-5 PACKAGE See Mech. Drawing
The DS1814/DS1819 ‘A’ and ‘C’ perform pushbutton reset control. They debounce the pushbutton input and generate an active reset pulse width of 140ms minimum. The DS1814/9 ‘A’ and ‘B’ versions perform a watchdog function. The watchdog is an internal timer th at forces the reset signals to the active state if the strobe input does not change state every 1.12 seconds. The watchdog timer function can be disabled by leaving the watchdog strobe input disconnected. OPERATION Power Monitor The DS1814 detects out-of-tolerance power supply c onditions and warns a processor-based system of impending power failure. When V CC falls below a preset level, a comparator outputs the signal RST (or RST). RST (or RST) are excellent control signals for a mic roprocessor, as processing is stopped at the last possible moment of valid VCC. On power-up, RST (or RST) are kept active for a minimum of 140ms to allow the power supply and processor to stabilize. Pushbutton Reset The DS1814 ‘A’ and ‘C’ provide an input pin for direct connection to a pushbutton reset (see Figure 2). The pushbutton reset input requires an active low sign al. Internally, this input is debounced and timed such that a RST (or RST) signal of at least 140ms minimum will be generated. The 140ms delay commences as the pushbutton reset input is released from the low level (see Figure 3). Watchdog Timer The DS1814/DS1819 ‘A’ and ‘B’ versions watchdog timer function forces RST (and RST) signal(s) active when the ST input is not clocked within the 1.12 s econd watchdog time-out period. Time-out of the watchdog starts when RST (and RST) become(s) inactive. If a 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 reset output(s) will go active for 140ms. The watchdog can be disabled by floating (or tri-stating) the ST input. The ST input can be derived from many microprocessor outputs. The most typical signals used are the microprocessor data I/O signals and 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 transition mu st occur at or less than 1.12 seconds. A typical circuit example is shown in Figure 4. The DS1814/19 watchdog function can be disabled at any time by tri-starting the strobe input. A sample circuit to disable the watchdog is shown in Figure 6.
DS1814/DS1819 BLOCK DIAGRAM Figure 1 *Notes: ST available on'A' and 'B' versions PBRST available on 'A' and 'C' versions RST available on 'B' and 'C' versions PUSHBUTTON RESET Figure 2 TIMING DIAGRAM: PUSHBUTTON RESET Figure 3
TIMING DIAGRAM: STROBE INPUT Figure 5 WATCHDOG DISABLE CIRCUIT Figure 6 TIMING DIAGRAM: POWER-DOWN Figure 7
TIMING DIAGRAM: POWER-UP Figure 8 RST VALID TO 0 VOLTS VCC Figure 9 OUTPUT VALID CONDITIONS The RST output uses a push-pull output which can maintain a valid output down to 1.0V V CC. To sink current below 1.0V a resistor can be connected form RST to Ground (see Figure 9.) This arrangement will maintain a valid value on RST during both power-up and -down but will draw current when RST is in the high state. A value of about 100k /g87/g32should be adequate in most situations. The output with a resistor pull-down can maintain a valid reset down to VCC equal to 0V.
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 V CC + 0.5V Operating Temperature Range -40 /g176C to +85/g176C Storage Temperature Range -55 /g176C to +125/g176C Soldering Temperature 260 /g176C 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/g176C to +85/g176C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Supply Voltage V CC 1.0 5.5 V 1 ST and PBRST Input High Level VIH 0.8 VCC V1 ST and PBRST Input Low Level VIL 0.3 VCC V1 DC ELECTRICAL CHARACTERISTICS (-40/g176C to +85/g176C; VCC = 1.2V to 5.5V) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES VCC Trip Point DS1814-5 V CCTP 4.50 4.75 V 1 VCC Trip Point DS1814-10 V CCTP 4.25 4.50 V 1 VCC Trip Point DS1819-5 V CCTP 3.00 3.15 V 1 VCC Trip Point DS1819-10 V CCTP 2.85 3.00 V 1 VCC Trip Point DS1819-20 V CCTP 2.55 2.70 V 1 Reset Trip Point Hysteresis (DS1814) V RH 10 mV Reset Trip Point Hysteresis (DS1819) V RH 5m V Output Current @ 2.4V I OH 350 /g109A 3 Output Current @ 0.4V I OL 3.2 6 mA 3 Output Voltage @ -30 /g109A VOH VCC*.8 V CC*.9 V 3 Operating Current DS1814 I CC 10 15 /g109A 4 Operating Current DS1819 I CC 81 2 /g109A 5 ST Input Current ST = VCC, Time Averaged 120 160 /g109A 6 ST Input Current ST = GND, Time Averaged -20 -15 /g109A 6
AC ELECTRICAL CHARACTERISTICS (-40/g176C to +85/g176C; VCC = 1.2V to 5.5V) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES PBRST = VIL tPB 1 /g109s 7 Reset Active Time t RST 140 200 280 ms ST Pulse Width tST 50 ns 8 Watchdog Time-out t TD 1.12 1.60 2.40 s VCC Detect to RST and RST tRPD 30 40 /g109s 9 VCC Slew Rate (rising edge) 12.5 V//g109s VCC Detect to RST and RST tRPU 140 200 280 ms PBRST Stable Low to RST and RST tPDLY 500 ns CAPACITANCE (tA = 25/g176C) PARAMETER SYMBOL MIN TYP MAX UNITS NOTES Input Capacitance C IN 5p F Output Capacitance C OUT 7p F NOTES: 1) All voltages are referenced to ground. 2) PBRST is internally pulled up to VCC with an internal impedance of 50k/g87/g32typical. 3) Measured with VCC/g32/g179/g322.7V. 4) Measured with outputs open, VCC /g163/g325.5V, and all inputs at VCC or Ground, except the ST input at <10kHz duty cycle-square wave or ST input open. 5) Measured with outputs open, VCC /g163/g323.6V, and all inputs at VCC or Ground, except the ST input at <10kHz duty cycle-square wave or ST input open. 6) The ST input current is defined as the average input current when ST is driven high or low. This input must be driven high or low by an output that can source or sink at least 200/g109A when active. 7) Noise immunity: pulses <100ns at pushbutton input will not cause a reset. 8) Must not exceed tTD minimum. 9) Noise immunity: pulses <2/g109s at VCCTP minimum will not cause a reset and VCCTP - VCC = 100mV.
‘A’, ‘B’ and ‘C’ represents the Device Type. 14A - DS1814A 14B - DS1814B 14C - DS1814C 19A - DS1819A 19B - DS1819B 19C - DS1819C ‘D’ represents the Device Tolerance. A - 5% B - 10% C - 20% SOT-23-5 PACKAGE