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DS1819CR-5-U+ ,5 Volt and 3.3 Volt MicroMonitorPIN DESCRIPTION Pin- and function-compatible with theDS181xAMAX823/24/25 products1 RST Active Low ..
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DXT3150-13 , NPN SURFACE MOUNT TRANSISTOR
DXT3904 , TECHNICAL SPECIFICATIONS OF NPN EPITAXIAL PLANAR TRANSISTOR
DXT3904-13 , NPN SURFACE MOUNT TRANSISTOR
DXT5551 , TECHNICAL SPECIFICATIONS OF NPN EPITAXIAL PLANAR TRANSISTOR
DXT651-13 , LOW VCE(SAT) NPN SURFACE MOUNT TRANSISTOR
DZ23C10 ,Zener DiodesDZ23C2V7–DZ23C51Vishay Telefunken300 mW Dual Surface Mount Zener Diodes
DS1814AR-5/T&R-DS1814CR-10-U+-DS1814CR-5/T&R-DS1819AR-10-U+-DS1819BR-10/T&R-DS1819CR-5-U+
5 Volt and 3.3 Volt MicroMonitor
FEATURESHalts and restarts an out-of-control
microprocessorHolds microprocessor in check during power
transientsAutomatically restarts microprocessor after
power failureMonitors pushbutton for external overrideAccurate 5%, 10%, or 20% (3V only)
microprocessor power monitoringEliminates the need for discrete components20% tolerance for use with 3.0V systemsPin- and function-compatible with the
MAX823/24/25 productsLow cost SOT-23-5 packageIndustrial temperature range: -40C to +85C
DEVICERSTRSTPBRSTWDDS181xA
DS181xB
DS181xC
x = "DS1814" for 5V devices
x = "DS1819" for 3V devices
PIN ASSIGNMENT
PIN DESCRIPTIONDS181xARSTActive Low Reset OutputGNDGroundPBRSTPushbutton Reset InputSTStrobe InputVCCPower Supply
DS181xBRSTActive Low Reset OutputGNDGroundRSTActive High Reset OutputSTStrobe InputVCCPower Supply
DS181xCRSTActive Low Reset OutputGNDGroundRSTActive High Reset OutputPBRSTPushbutton Reset Input
5 VCCPower Supply
DESCRIPTIONThe 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 VCC. When an out-of-tolerance
condition occurs, an internal power-fail signal is generated which forces the reset(s) to an active state.
DS1814/DS1819
5V and 3.3V MicroMonitor
1
SOT-23-5 PACKAGE
See Mech. Drawing
DS1814/DS1819
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 that 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 MonitorThe DS1814 detects out-of-tolerance power supply conditions and warns a processor-based system of
impending power failure. When VCC falls below a preset level, a comparator outputs the signal RST (or
RST). RST (or RST) are excellent control signals for a microprocessor, 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 ResetThe 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 signal. 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 TimerThe 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 second 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 must 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
DS1814/DS1819 BLOCK DIAGRAM Figure 1
*Notes: 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
DS1814/DS1819
WATCHDOG TIMER Figure 4
TIMING DIAGRAM: STROBE INPUT Figure 5
WATCHDOG DISABLE CIRCUIT Figure 6
TIMING DIAGRAM: POWER-DOWN Figure 7
DS1814/DS1819
TIMING DIAGRAM: POWER-UP Figure 8
RST VALID TO 0 VOLTS VCC Figure 9
OUTPUT VALID CONDITIONSThe RST output uses a push-pull output which can maintain a valid output down to 1.0V VCC. 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 100kshould be adequate in most situations. The output with a
resistor pull-down can maintain a valid reset down to VCC equal to 0V.
DS1814/DS1819
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 Range-40C to +85C
Storage Temperature Range-55C to +125C
Soldering Temperature 260C for 10 secondsThis 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 (-40C to +85C)
PARAMETERSYMBOLMINTYPMAXUNITSNOTESSupply VoltageVCC1.05.5V1 and PBRST Input High LevelVIH0.8 VCCV1 and PBRST Input Low LevelVIL0.3 VCCV1
DC ELECTRICAL CHARACTERISTICS (-40C to +85C; VCC = 1.2V to 5.5V)
PARAMETERSYMBOLMINTYPMAXUNITSNOTESVCC Trip Point DS1814-5VCCTP4.504.75V1
VCC Trip Point DS1814-10VCCTP4.254.50V1
VCC Trip Point DS1819-5VCCTP3.003.15V1
VCC Trip Point DS1819-10VCCTP2.853.00V1
VCC Trip Point DS1819-20VCCTP2.552.70V1
Reset Trip Point Hysteresis (DS1814)VRH10mV
Reset Trip Point Hysteresis (DS1819)VRH5mV
Output Current @ 2.4VIOH350A3
Output Current @ 0.4VIOL3.26mA3
Output Voltage @ -30 AVOHVCC*.8VCC*.9V3
Operating Current DS1814ICC1015A4
Operating Current DS1819ICC812A5 Input Current = VCC, Time Averaged
120160A6 Input Current = GND, Time Averaged
-20-15A6
