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Low-Cost, µP Supervisory Circuits
General DescriptionThe MAX705–MAX708/MAX813L microprocessor (µP)
supervisory circuits reduce the complexity and number of
components required to monitor power-supply and battery functions in µP systems. These devices signiicantly improve
system reliability and accuracy compared to separate ICs or
discrete components.
The MAX705/MAX706/MAX813L provide four functions:
1) A reset output during power-up, power-down, and
brownout conditions.
2) An independent watchdog output that goes low if
the watchdog input has not been toggled within 1.6
seconds.
3) A 1.25V threshold detector for power-fail warning, low-
battery detection, or for monitoring a power supply
other than +5V.
4) An active-low manual-reset input.
The MAX707/MAX708 are the same as the MAX705/
MAX706, except an active-high reset is substituted for
the watchdog timer. The MAX813L is the same as the
MAX705, except RESET is provided instead of RESET.
Two supply-voltage monitor levels are available: The
MAX705/MAX707/MAX813L generate a reset pulse when
the supply voltage drops below 4.65V, while the MAX706/
MAX708 generate a reset pulse below 4.40V. All four parts
are available in 8-pin DIP, SO, and µMAX® packages.
Applications●Computers●Controllers●Intelligent Instruments●Critical μP Power Monitoring
Beneits and Features●Supervisory-Function Integration Significantly
Improves System Reliability While Reducing Board
SpaceμMAX PackageGuaranteed RESET Valid at VCC = 1V-200ms Reset Pulse Width-Debounced TTL/CMOS-Compatible Manual-
Reset Input-Active-High Reset Output (MAX707/MAX708/
MAX813L)Precision-Supply Voltage Monitor-4.65V (MAX705/MAX707/MAX813L)-4.40V (MAX706/MAX708)Voltage Monitor for Power-Fail or Low-Battery
Warning
µMAX is a registered trademark of Maxim Integrated Products, Inc.
*Dice are specified at TA = +25°C.
**Contact factory for availability and processing to MIL-STD-883. Devices in PDIP, SO, and μMAX packages are available in both
leaded and lead(Pb)-free/RoHS-compliant packaging. Specify lead-free by adding the + symbol at the endof the part number when ordering.
Lead-free packaging is not available for CERDIP packages.
PARTTEMP RANGEPIN-PACKAGE
MAX705CPA0°C to +70°C8 Plastic DIP
MAX705CSA0°C to +70°C8 SO
MAX705CUA0°C to +70°C8 μMAX
MAX705C/D0°C to +70°CDice*
Pin Configurations appear at end of data sheet.
Ordering Information continued at end of data sheet.VCC
PFIPFO
WDO
RESET
UNREGULATED DC
PUSHBUTTON
SWITCH
PFII/O LINE
INTERRUPT
MAX705
MAX706
MAX813L
MAX667+5V DC LINEAR
REGULATOR
VCC
RESET
NMI
MAX705–MAX708/MAX813LLow-Cost, μP Supervisory Circuits
Typical Operating Circuit
Ordering Information
Terminal Voltage (with respect to GND)
VCC .....................................................................-0.3V to 6.0VAll Other Inputs (Note 1) .....................-0.3V to (VCC + 0.3V)
Input Current
VCC .................................................................................20mA
GND ...............................................................................20mA
Output Current (all outputs) ................................................20mA
Continuous Power Dissipation (TA = +70°C)Plastic DIP (derate 9.09mW/°C above +70°C) ............727mWSO (derate 5.88mW/°C above +70°C) ........................471mW μMAX (derate 4.10mW/°C above +70°C) ...................330mWCERDIP (derate 8.00mW/°C above +70°C) ................640mW
Operating Temperature RangesMAX70_C__, MAX813LC__ ...............................0°C to +70°CMAX70_E__, MAX813LE__ ..........................-40°C to +85°C
MAX70_MJA .................................................-55°C to +125°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow)
Lead(Pb)-free...............................................................+260°CContaining Lead(Pb) ....................................................+240°C
(VCC = 4.75V to 5.5V for MAX705/MAX707/MAX813L, VCC = 4.5V to 5.5V for MAX706/MAX708, TA = TMIN to TMAX, unless otherwise
noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Voltage RangeVCC
MAX70_C1.05.5MAX813LC1.15.5
MAX70_E/M, MAX813LE/M1.25.5
Supply CurrentISUPPLY
MAX705C, MAX706C, MAX813LC150350MAX705E/M, MAX706E/M, MAX813LE/M150500
MAX707C, MAX708C50350
MAX707E/M, MAX708E/M50500
Reset Threshold (Note 2)VRT
MAX705, MAX707, MAX813L4.504.654.75MAX706, MAX7084.254.404.50
Reset Threshold Hysteresis (Note 2)40mV
Reset Pulse Width (Note 2)tRS140200280ms
RESET Output Voltage
ISOURCE = 800μAVCC - 1.5ISINK = 3.2mA0.4
MAX70_C, VCC = 1V, ISINK = 50μA0.3
MAX70_E/M, VCC = 1.2V, ISINK = 100μA0.3
RESET Output Voltage
MAX707, MAX708, ISOURCE = 800μAVCC - 1.5
MAX707, MAX708, ISINK = 1.2mA0.4
MAX813LC, ISOURCE = 4μA, VCC = 1.1V0.8
MAX813LE/M, ISOURCE = 4μA, VCC = 1.2V0.9
MAX813L
ISOURCE = 800μAVCC - 1.5
ISINK = 3.2mA0.4
MAX705–MAX708/MAX813LMAX705–MAX708/MAX813L Low-Cost, μP Supervisory Circuits
Note 1: The input-voltage limits on PFI and MR can be exceeded if the input current is less than 10mA.
Absolute Maximum RatingsStresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Electrical Characteristics
(VCC = 4.75V to 5.5V for MAX705/MAX707/MAX813L, VCC = 4.5V to 5.5V for MAX706/MAX708, TA = TMIN to TMAX, unless otherwise
noted.)
Note 2: Applies to both RESET in the MAX705–MAX708 and RESET in the MAX707/MAX708/MAX813L.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSWatchdog Timeout PeriodtWDMAX705, MAX706, MAX813L1.001.602.25s
WDI Pulse WidthtWPVIL = 0.4V, VIH = (VCC) (0.8)50ns
WDI Input Threshold
Low
MAX705, MAX706, MAX813L, VCC = 5V
High3.5
WDI Input CurrentMAX705, MAX706, MAX813L, VCC = 5V50150µA
MAX705, MAX706, MAX813L, WDI = 0V-150-50
WDO Output Voltage
MAX705, MAX706, MAX813L,
ISOURCE = 800μAVCC - 1.5
MAX705, MAX706, MAX813L,
ISINK = 1.2mA0.4
MR Pull-Up CurrentMR = 0V100250600μA
MR Pulse WidthtMR150ns
MR Input ThresholdLow0.8V
High2.0
MR to Reset Out Delay (Note 2)tMD250ns
PFI Input ThresholdVCC = 5V1.201.251.30V
PFI Input Current-25.00+0.01+25.00nA
PFO Output Voltage
ISOURCE = 800μAVCC - 1.5ISINK = 3.2mA0.4
MAX705–MAX708/MAX813LMAX705–MAX708/MAX813L Low-Cost, μP Supervisory Circuits
Electrical Characteristics (continued)
MAX705/MAX707
RESET RESPONSE TIME2µs/div
VCC
+5V
RESET
+5V
+4V
1V/div
TA = +25°C
VCC
GND
RESET
VCC10kΩ
RESET
30pF
MAX705 toc02
POWER-FAIL COMPARATOR
DE-ASSERTION RESPONSE TIME400ns/div
PFI
+1.20V
PFO
+3V
+1.30V
VCC = +5V
TA = +25°C
+5V
PFO
30pF1kΩ
+1.25V
PFI
MAX705 toc08
POWER-FAIL COMPARATOR
ASSERTION RESPONSE TIME400ns/div
PFI
+1.30V
PFO
+5V
+1.20V
1V/div
50mV/div
+5V
PFO
30pF
1kΩ
+1.25V
PFI
VCC = +5V
TA = +25°C
MAX705 toc04
MAX707
RESET, RESET ASSERTION400ns/div
+5V
RESET
RESET
1V/div
VCC = VRT
TA = +25°C
+5V
VCC
GND
RESET10k
330pF
RESET
10kΩ
330pF
MAX705 toc05
MAX707
RESET, RESET DE-ASSERTION400ns/div
+5V
RESET
RESET
2V/div
VCC = VRT
TA = +25°C
+5V
VCC
GND
RESET
RESET
10kΩ
330pF
10k
330pF
MAX705 toc06
MAX707/MAX708/MAX813L
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGEVCC
RESET
+5V
1V/div
+5V
1V/div
TA = +25°C
GND
RESET
VCC
330pF10kΩ
MAX705 toc07
MAX705/MAX707
RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE500ms/div
VCC
RESET
+5V
1V/div
+5V
1V/div
VCC
GND
RESET
VCC2kΩ
RESET
330pF
TA = +25°C
MAX705 toc01
MAX813L
RESET RESPONSE TIME+5V
VCC
+4V
+4V
GND
RESET
VCC
330pF10kΩ
MAX705 toc08
MAX705–MAX708/MAX813LMAX705–MAX708/MAX813L Low-Cost, μP Supervisory Circuits
Typical Operating Characteristics
PIN
NAMEFUNCTIONMAX705/MAX706MAX707/MAX708MAX813L
DIP/SOμMAXDIP/SOμMAXDIP/SOμMAX31313MR
Manual-Reset Input triggers a reset pulse when
pulled below 0.8V. This active-low input has an internal 250μA pullup current. It can be driven from a
TTL or CMOS logic line, as well as shorted to ground
with a switch.42424VCC+5V Supply Input53535GND0V Ground Reference for all signals64646PFI
Power-Fail Voltage-Monitor Input. When PFI is less
than 1.25V, PFO goes low. Connect PFI to GND or
VCC when not used.75757PFOPower-Fail Output goes low and sinks current when
PFI is less than 1.25V; otherwise PFO stays high.8——68WDI
Watchdog Input. If WDI remains high or low for
1.6sec, the internal watchdog timer runs out and
WDO goes low (Figure 1). Floating WDI or connecting
WDI to a high-impedance three-state buffer disables
the watchdog feature. The internal watchdog timer
clears whenever reset is asserted, WDI is three
stated, or WDI sees a rising or falling edge.—6———N.C.No Connect171——RESET
Active-Low Reset Output pulses low for 200ms when
triggered, and stays low whenever VCC is below the
reset threshold (4.65V in the MAX705 and 4.40V in
the MAX706). It remains low for 200ms after VCC
rises above the reset threshold or MR goes from low
to high (Figure 3). A watchdog timeout will not trigger
RESET unless WDO is connected to MR.2——82WDO
Watchdog Output pulls low when the internal watchdog timer inishes its 1.6sec count and does
not go high again until the watchdog is cleared. WDO
also goes low during low-line conditions. Whenever
VCC is below the reset threshold, WDO stays low;
however, unlike RESET, WDO does not have a
minimum pulse width. As soon as VCC rises above
the reset threshold, WDO goes high with no delay.—8271RESET
Active-High RESET Output is the inverse of RESET.
Whenever RESET is high, RESET is low, and vice
versa (Figure 2). The MAX813L has a RESET output
only.
MAX705–MAX708/MAX813LMAX705–MAX708/MAX813L Low-Cost, μP Supervisory Circuits
Pin Description
Detailed Description
Reset OutputA microprocessor’s (μP’s) reset input starts the μP in a known state. Whenever the μP is in an unknown state, it
should be held in reset. The MAX705–MAX708/MAX813L
assert reset during power-up and prevent code execution
errors during power-down or brownout conditions.
On power-up, once VCC reaches 1V, RESET is a
guaranteed logic low of 0.4V or less. As VCC rises, RESET
stays low. When VCC rises above the reset threshold, an
internal timer releases RESET after about 200ms. RESET
pulses low whenever VCC dips below the reset threshold,
i.e. brownout condition. If brownout occurs in the middle
of a previously initiated reset pulse, the pulse continues
for at least another 140ms. On power-down, once VCC
falls below the reset threshold, RESET stays low and is
guaranteed to be 0.4V or less until VCC drops below 1V.
The MAX707/MAX708/MAX813L active-high RESET
output is simply the complement of the RESET output,
and is guaranteed to be valid with VCC down to 1.1V. Some μPs, such as Intel’s 80C51, require an active-high
reset pulse.
Watchdog TimerThe MAX705/MAX706/MAX813L watchdog circuit monitors the μP’s activity. If the μP does not toggle the
stated, WDO goes low. As long as RESET is asserted or
the WDI input is three stated, the watchdog timer stays
cleared and will not count. As soon as reset is released
and WDI is driven high or low, the timer starts counting.
Pulses as short as 50ns can be detected.
Typically, WDO is not connected to the nonmaskable interrupt input (NMI) of a μP. When VCC drops below
the reset threshold, WDO goes low whether or not
the watchdog timer has timed out yet. Normally this
would trigger an NMI interrupt, but RESET goes low
simultaneously, and thus overrides the NMI interrupt.
If WDI is left unconnected, WDO can be used as a low-line output. Since loating WDI disables the internal timer,
WDO goes low only when VCC falls below the reset
threshold, thus functioning as a low-line output.
The MAX705/MAX706 have a watchdog timer and a
RESET output. The MAX707/MAX708 have both active-
high and active-low reset outputs. The MAX813L has both
an active-high reset output and a watchdog timer.
Manual ResetThe manual-reset input (MR) allows reset to be triggered
by a pushbutton switch. The switch is effectively
debounced by the 140ms minimum reset pulse width. MR
is TTL/CMOS-logic compatible, so it can be driven by an
external logic line. MR can be used to force a watchdog
timeout to generate a reset pulse in the MAX705/ MAX706/
Figure 1. MAX705/MAX706/MAX813L Block DiagramFigure 2. MAX707/MAX708 Block Diagram
WATCHDOG
TIMER
TIMEBASE FOR
RESET AND
WATCHDOG
RESET
GENERATOR
VCC
250µAWDORESET
(RESET)PFO
GND3
1.25V
4.65V*
* 4.40V FOR MAX7O6. ( ) ARE FOR MAX813L ONLY.WDIMRVCCPFI
MAX705
MAX706
MAX813LWATCHDOG
TRANSITION
DETECTOR
RESET
GENERATORRESETRESETPFO
1.25V
4.65V*
* 4.40V FOR MAX7O6. MRVCCPFI
MAX707
MAX708VCC
250µA
GND3
MAX705–MAX708/MAX813LMAX705–MAX708/MAX813L Low-Cost, μP Supervisory Circuits
