Dallas DS1814C 5v and 3.3v micromonitor Datasheet

DS1814/DS1819
5V and 3.3V MicroMonitor
www.maxim-ic.com
FEATURES
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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 5%, 10%, or 20% (3V only)
microprocessor power monitoring
Eliminates the need for discrete components
20% tolerance for use with 3.0V systems
Pin- and function-compatible with the
MAX823/24/25 products
Low cost SOT-23-5 package
Industrial temperature range: -40°C to +85°C
DEVICE
RST
RST
DS181xA
X
DS181xB
X
X
DS181xC
X
X
x = "DS1814" for 5V devices
x = "DS1819" for 3V devices
PBRST
WD
X
X
X
3
4
2
1
5
SOT-23-5 PACKAGE
See Mech. Drawing
PIN DESCRIPTION
X
DS181xA
1
RST
2 GND
PBRST
3
4 ST
5 VCC
Active Low Reset Output
Ground
Pushbutton Reset Input
Strobe Input
Power Supply
DS181xB
1
RST
2 GND
3 RST
4 ST
5 VCC
Active Low Reset Output
Ground
Active High Reset Output
Strobe Input
Power Supply
DS181xC
1
RST
2 GND
3 RST
4
PBRST
5 VCC
Active Low Reset Output
Ground
Active High Reset Output
Pushbutton Reset Input
Power Supply
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 temperaturecompensated 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.
When VCC 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.
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122001
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 Monitor
The 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 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 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 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 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.
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DS1814/DS1819
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
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DS1814/DS1819
WATCHDOG TIMER Figure 4
TIMING DIAGRAM: STROBE INPUT Figure 5
WATCHDOG DISABLE CIRCUIT Figure 6
TIMING DIAGRAM: POWER-DOWN Figure 7
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DS1814/DS1819
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 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 100kW should be adequate in most situations. The output with a
resistor pull-down can maintain a valid reset down to VCC equal to 0V.
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DS1814/DS1819
ABSOLUTE MAXIMUM RATINGS*
Voltage on VCC Pin Relative to Ground
Voltage on I/O Relative to Ground
Operating Temperature Range
Storage Temperature Range
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
SYMBOL
VCC
MIN
1.0
ST and PBRST Input High Level
VIH
0.8 VCC
ST and PBRST Input Low Level
VIL
TYP
MAX
5.5
0.3 VCC
DC ELECTRICAL CHARACTERISTICS
PARAMETER
(-40°C to +85°C)
UNITS
V
NOTES
1
V
1
V
1
(-40°C to +85°C; VCC = 1.2V to 5.5V)
SYMBOL
MIN
VCC Trip Point DS1814-5
VCCTP
VCC Trip Point DS1814-10
TYP
MAX
UNITS
NOTES
4.50
4.75
V
1
VCCTP
4.25
4.50
V
1
VCC Trip Point DS1819-5
VCCTP
3.00
3.15
V
1
VCC Trip Point DS1819-10
VCCTP
2.85
3.00
V
1
VCC Trip Point DS1819-20
VCCTP
2.55
2.70
V
1
Reset Trip Point Hysteresis (DS1814)
VRH
10
mV
Reset Trip Point Hysteresis (DS1819)
VRH
5
mV
Output Current @ 2.4V
IOH
350
mA
3
Output Current @ 0.4V
IOL
3.2
6
mA
3
Output Voltage @ -30 mA
VOH
VCC*.8
VCC*.9
V
3
Operating Current DS1814
ICC
10
15
mA
4
Operating Current DS1819
ICC
8
12
mA
5
120
160
mA
6
mA
6
ST Input Current
ST = VCC, Time Averaged
-20
ST Input Current
ST = GND, Time Averaged
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DS1814/DS1819
AC ELECTRICAL CHARACTERISTICS
PARAMETER
(-40°C to +85°C; VCC = 1.2V to 5.5V)
SYMBOL
tPB
MIN
1
TYP
Reset Active Time
tRST
140
200
ST Pulse Width
tST
50
Watchdog Time-out
tTD
1.12
VCC Detect to RST and RST
tRPD
PBRST = VIL
VCC Slew Rate (rising edge)
MAX
ms
280
tRPU
PBRST Stable Low to RST and RST
tPDLY
140
1.60
2.40
s
30
40
ms
Output Capacitance
8
9
V/ms
200
280
500
ms
ns
CAPACITANCE
PARAMETER
Input Capacitance
NOTES
7
ms
ns
12.5
VCC Detect to RST and RST
UNITS
(tA = 25°C)
SYMBOL
CIN
MIN
TYP
MAX
5
UNITS
pF
7
pF
COUT
NOTES
NOTES:
1) All voltages are referenced to ground.
2) PBRST is internally pulled up to VCC with an internal impedance of 50kW typical.
3) Measured with VCC ³ 2.7V.
4) Measured with outputs open, VCC £ 5.5V, 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 £ 3.6V, 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 200mA 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 <2ms at VCCTP minimum will not cause a reset and VCCTP - VCC = 100mV.
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DS1814/DS1819
PART MARKING CODES
SOT-23-5 PACKAGE
‘D’ represents the Device Tolerance.
‘A’, ‘B’ and ‘C’ represents the Device Type.
14A
14B
14C
19A
19B
19C
-
A
B
C
DS1814A
DS1814B
DS1814C
DS1819A
DS1819B
DS1819C
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5%
10%
20%
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