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MAX690RCSA+ |MAX690RCSAMAXIMN/a22avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690RESA+N/AN/a2500avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690RESA+ |MAX690RESAMAXIMN/a22avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690SCSA+ |MAX690SCSAMAXIMN/a9avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690SESA+ |MAX690SESAMAXIMN/a18avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690TCSA+ |MAX690TCSAMAXIMN/a12avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690TESA+MAXICN/a2500avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX690TESA+ |MAX690TESAMAXIMN/a120avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704RCSA+ |MAX704RCSAMAXIMN/a50avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704TCSA+ |MAX704TCSAMAXN/a28avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704TESA+ |MAX704TESAMAXIMN/a55avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704RCSA+TMAXIMN/a1500avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SCSA+ |MAX704SCSAMAXIMN/a135avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SCSA+T |MAX704SCSATMAXIMN/a2181avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SCSA+T |MAX704SCSATMAXIM Pb-freeN/a1632avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SESA+ |MAX704SESAMAXIMN/a180avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SESA-T |MAX704SESATMAXIMN/a5087avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704SESA+T |MAX704SESATMAXIMN/a435avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX704TCSA+T |MAX704TCSATMAXIMN/a13930avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX805SCSA+ |MAX805SCSAMAXIMN/a30avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX805SCSA+TMAXIMN/a637avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX806SESA+TMAXIMN/a11avai3.0V/3.3V Microprocessor Supervisory Circuits
MAX806TCSA+ |MAX806TCSAMAXIMN/a90avai3.0V/3.3V Microprocessor Supervisory Circuits


MAX704TCSA+T ,3.0V/3.3V Microprocessor Supervisory CircuitsFeaturesThese microprocessor (µP) supervisory circuits reduce the ● RESET and RESET Outputscomplexi ..
MAX704TESA ,3.0V or 3.3V microprocessor supervisory circuit. Reset threshold 3.075V. Active-low reset. Manual reset input. Backup-battery switch. Power-fail threshold accuracy +-4%. Power-fail comparator. Reset window +-75mVGeneral Description ________
MAX704TESA ,3.0V or 3.3V microprocessor supervisory circuit. Reset threshold 3.075V. Active-low reset. Manual reset input. Backup-battery switch. Power-fail threshold accuracy +-4%. Power-fail comparator. Reset window +-75mVFeatures– — — — — –These microprocessor (µP) supervisory circuits reduce' RESET and RESET Outputsth ..
MAX704TESA ,3.0V or 3.3V microprocessor supervisory circuit. Reset threshold 3.075V. Active-low reset. Manual reset input. Backup-battery switch. Power-fail threshold accuracy +-4%. Power-fail comparator. Reset window +-75mVMAX690T/S/R, 704T/S/R, 802T/S/R, 804–806T/S/RReset WindowPower-Fail ComparatorPower-Fail Threshold ..
MAX704TESA+ ,3.0V/3.3V Microprocessor Supervisory CircuitsReset WindowPower-Fail ComparatorPower-Fail Threshold Accuracy Backup-Battery Switch Manual Rese ..
MAX705 ,Low-Cost, µP Supervisory CircuitsApplications lead-free by adding the + symbol at the endof the part number when ordering. ● Comput ..
MB40768H ,D/A Converter (1-ch, 8-bit, 60 MSPS)FEATURES• Resolution: 8 bits• Conversion characteristics: Maximum conversion rate: 60 MSPS [min.]Li ..
MB40768HP ,D/A Converter (1-ch, 8-bit, 60 MSPS)FEATURES• Resolution: 8 bits• Conversion characteristics: Maximum conversion rate: 60 MSPS [min.]Li ..
MB40768HPF ,D/A Converter (1-ch, 8-bit, 60 MSPS)FUJITSU SEMICONDUCTORDS04-28313-1EDATA SHEETASSP Image ProcessingBIPOLARD/A Converter (1-ch, 8-b ..
MB40776H , 1 Channel 6-bit D/A converter
MB40778PF , C-MOS 8-BIT VIDEO D/A CONVERTER
MB408 , 40 Amp Single Phase Bridge Rectifier 50 to 1000 Volts


MAX690RCSA+-MAX690RESA+-MAX690SCSA+-MAX690SESA+-MAX690TCSA+-MAX690TESA+-MAX704RCSA+-MAX704RCSA+T-MAX704SCSA+-MAX704SCSA+T-MAX704SESA+-MAX704SESA+T-MAX704SESA-T-MAX704TCSA+-MAX704TCSA+T-MAX704TESA+-MAX805SCSA+-MAX805SCSA+T-MAX806SESA+T-MAX806TCSA+
3.0V/3.3V Microprocessor Supervisory Circuits
General Description
These microprocessor (µP) supervisory circuits reduce the
complexity and number of components required for pow-
er-supply monitoring and battery-control functions in µP
systems. They significantly improve system reliability and
accuracy compared to separate ICs or discrete components.
These devices are designed for use in systems powered
by 3.0V or 3.3V supplies. See the selector guide in the
back of this data sheet for similar devices designed for
5V systems. The suffixes denote different reset threshold
voltages: 3.075V (T), 2.925V (S), and 2.625V (R) (see the
Reset Threshold section in the Detailed Description). All
these parts are available in 8-pin DIP and SO packages.
Functions offered in this series are as follows:
Features
●RESET and RESET Outputs●Manual Reset Input●Precision Supply-Voltage Monitor●200ms Reset Time Delay●Watchdog Timer (1.6sec timeout)●Battery-Backup Power Switching—Battery Can
Exceed VCC in Normal Operation●40µA VCC Supply Current●1µA Battery Supply Current●Voltage Monitor for Power-Fail or Low-Battery
Warning●Guaranteed RESET Assertion to VCC = 1V●8-Pin DIP and SO Packages
Applications
●Battery-Powered Computers and Controllers●Embedded Controllers●Intelligent Instruments●Critical µP Power Monitoring●Portable Equipment
Pin Configuration appears at end of data sheet.Typical Operating Circuits continued at at end of data
sheet.
Ordering Information continued at end of data sheet.
*Contact factory for dice specifications.
**These parts offer a choice of reset threshold voltage. Select

the letter corresponding to the desired nominal reset threshold
voltage (T = 3.075V, S = 2.925V, R = 2.625V) and insert it into
the blank to complete the part number.
Devices in PDIP and SO packages are available in both leaded
and lead(Pb)-free packaging. Specify lead free by adding the +
symbol at the end of the part number when ordering. Lead free
not available for CERDIP package.
PART**TEMP RANGEPIN-PACKAGE
MAX690_CPA
0°C to +70°C8 Plastic DIP
MAX690_CSA0°C to +70°C8 SO
MAX690_C/D0°C to +70°CDice*
MAX690_EPA-40°C to +85°C8 Plastic DIP
MAX690_ESA-40°C to +85°C8 SO
MAX690_MJA-55°C to +125°C8 CERDIP
MAX690T/S/RMAX802T/S/R
MAX804T/S/R
MAX805T/S/R

0.1µF
VOUT
RESET
(RESET)
PFO
WDI
VBATT
VCC
GND
GND
GND
VCC
0.1µF0.1µF
3.6V
LITHIUM
BATTERY
CMOS RAMVCC
RESET
NMI
I/O LINE
UNREGULATED
REGULATED +3.3V OR +3.0VBUS
( ) ARE FOR MAX804T/S/R, MAX805T/S/R
PFI
Active-Low Reset Active-High Reset Watchdog Input Manual Reset Input Backup-Battery SwitchPower-Fail Threshold Accuracy
Power-Fail ComparatorReset Window

MAX690±4%±75mV
MAX704±4%±75mV
MAX802±2%±2%
MAX804±2%±2%
MAX805±4%±75mV
MAX806±2%±2%
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804‒MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
Typical Operating Circuits
Ordering Information
(VCC = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25°C.)
Terminal Voltage (with respect to GND)
VCC ...................................................................-0.3V to +6.0V
VBATT ..............................................................-0.3V to +6.0V
All Other Inputs.................-0.3V to the higher of VCC or VBATT
Continuous Input Current
VCC ...............................................................................100mA
VBATT ............................................................................18mA
GND ................................................................................18mA
Output Current
RESET, PFO ..................................................................18mA
VOUT .............................................................................100mA
Continuous Power Dissipation (TA = +70°C)
Plastic DIP (derate 9.09mW/°C above +70°C) ............727mW
SO (derate 5.88mW/°C above +70°C) ........................471mW
CERDIP (derate 8.00mW/°C above +70°C) ................640mW
Operating Temperature Ranges
MAX690_C_ _/MAX704_C_ _/MAX80_ _C_ _ .......0°C to +70°C
MAX690_E_ _/MAX704_E_ _/MAX80_ _E_ _. ...-40°C to +85°C
MAX690_M_ _/MAX704_M_ _/MAX80_ _M_ _ ...-55°C to +125°C
Storage Temperature Range ............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

Operating Voltage Range,
VCC, VBATT (Note 1)
MAX690_C, MAX704_C, MAX80_ _C1.05.5VMAX690_E/M, MAX704_E/M, MAX80_ _E/M1.15.5
VCC Supply Current
(excluding IOUT)ISUPPLY
MR = VCC
(MAX704_/
MAX806_)
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC < 3.6V4050
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E, VCC < 5.5V5065
MAX690_M, MAX704_M,
MAX80_ _M, VCC < 3.6V4055
MAX690_M, MAX704_M,
MAX80_ _M, VCC < 5.5V5070
VCC Supply Current in Battery-
Backup Mode(excluding IOUT)
MR = VCC
(MAX704_/
MAX806_)
VCC = 2.0V, VBATT = 2.3V2550µA
VBATT Supply Current, Any
Mode (excluding IOUT) (Note 2)
MAX690_C/E, MAX704_C/E, MAX80_ _C/E0.41µAMAX690_M, MAX704_M, MAX80_ _M0.410
Battery Leakage Current
(Note 3)
MAX690_C/E, MAX704_C/E, MAX80_ _C/E0.010.5µAMAX690_M, MAX704_M, MAX80_ _M0.015
VOUT Output Voltage
MAX690_C/E, MAX704_C/E, MAX80_ _C/E,
IOUT = 5mA (Note 4)
VCC
VCC
MAX690_C/E, MAX704_C/E, MAX80_ _C/E
IOUT = 50mA
VCC
VCC
MAX690_M, MAX704_M, MAX80_ _M
IOUT = 5mA (Note 4)
VCC
VCC
MAX690_M, MAX704_M, MAX80_ _M
IOUT = 50mA
VCC
VCC
IOUT = 250µA, VCC > 2.5V (Note 4)VCC
VCC
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
Absolute Maximum Ratings

Stresses 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 = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

VOUT in Battery-Backup
Mode
IOUT = 250µA, VBATT = 2.3VVBATT
- 0.1
VBATT
- 0.034
IOUT = 1mA, VBATT = 2.3VVBATT
Battery Switch Threshold,
VCC Falling
VBATT - VCC, VSW > VCC > 1.75V (Note 5)6525mV
VSWVBATT > VCC (Note 6)2.302.402.50V
Battery Switch Threshold,
VCC Rising (Note 7)
This value is identical to the reset threshold,
VCC risingV
Reset Threshold (Note 8)VRST
MAX690T/704T/805T
VCC falling3.003.0753.15
VCC rising3.003.0853.17
MAX802T/804T/806TVCC falling3.003.0753.12
VCC rising3.003.0853.14
MAX690S/704S/805SVCC falling2.852.9253.00
VCC rising2.852.9353.02
MAX802S/804S/806SVCC falling2.882.9253.00
VCC rising2.882.9353.02
MAX690R/704R/805RVCC falling2.552.6252.70
VCC rising2.552.6352.72
MAX802R/804R/806S
VCC falling2.592.6252.70
VCC rising2.592.6352.72
Reset Timeout PeriodtWPVCC < 3.6V140200280ms
PFO, RESET Output VoltageVOHISOURCE = 50µAVCC-
VCC-
0.05V
PFO, RESET Output Short to
GND Current (Note 4)IOSVCC = 3.3V, VOH = 0V180500µV
PFO, RESET, RESET
Output VoltageVOL
ISINK = 1.2mA;
MAX690_/704_/802_/806_, VCC = VRST min;
MAX804_/805_, VCC = VRST max
0.060.3V
PFO, RESET Output VoltageVOL
VBATT = 0V, VCC = 1.0V, ISINK = 40µA,
MAX690_C, MAX704_C, MAX80_ _C0.130.3
VBATT = 0V, VCC = 1.2V, ISINK = 200µA,
MAX690_E/M, MAX704_E/M, MAX80_ _E/M0.170.3
RESET Output Leakage
Current (Note 9)
VBATT = 0V,
VCC = VRST min;
VRESET = 0V, VCC
MAX804_C,
MAX805_C-1+1
MAX804_E/M,
MAX805_E/M-10+10
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
Electrical Characteristics (continued)
(VCC = 3.17V to 5.5V for the MAX690T/MAX704T/MAX80_T, VCC = 3.02V to 5.5V for the MAX690S/MAX704S/MAX80_S, VCC = 2.72V to
5.5V for the MAX690R/MAX704R/MAX80_R; VBATT = 3.6V; TA = TMIN to TMAX; unless otherwise noted. Typical values are at TA = +25C.)
Note 1: VCC supply current, logic input leakage, watchdog functionality (MAX690_/802_/805_/804_), MR functionality

(MAX704_/806_), PFI functionality, state of RESET (MAX690_/704_/802_/806_), and RESET (MAX804_/805_) tested at
VBATT = 3.6V, and VCC = 5.5V. The state of RESET or RESET and PFO is tested at VCC = VCC min.
Note 2:
Tested at VBATT = 3.6V, VCC = 3.5V and 0V. The battery current will rise to 10µA over a narrow transition window around
VCC = 1.9V.
Note 3:
Leakage current into the battery is tested under the worst-case conditions at VCC = 5.5V, VBATT = 1.8V and at VCC = 1.5V,
VBATT= 1.0V.
Note 4:
Guaranteed by design.
Note 5:
When VSW > VCC > VBATT, VOUT remains connected to VCC until VCC drops below VBATT. The VCC-to-VBATT compara-
tor has a small 25mV typical hysteresis to prevent oscillation. For VCC < 1.75V (typ), VOUT switches to VBATT regardless
of the voltage on VBATT.
Note 6: When VBATT > VCC > VSW, VOUT remains connected to VCC until VCC drops below the battery switch threshold (VSW).
Note 7:
VOUT switches from VBATT to VCC when VCC rises above the reset threshold, independent of VBATT. Switchover back to
VCC occurs at the exact voltage that causes RESET to go high (on the MAX804_/805_, RESET goes low); however
switchover occurs 200ms prior to reset.
Note 8:
The reset threshold tolerance is wider for VCC rising than for VCC falling to accommodate the 10mV typical hysteresis,
which prevents internal oscillation.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS

PFI Input ThresholdVPFTVCC < 3.6V
VPFI falling
MAX802_C/E, MAX804_C/E,
MAX806_C/E1.2121.2371.262V
MAX690_/MAX704_/MAX805_1.1871.2371.287
PFI Input Current
MAX690_C/E, MAX704_C/E, MAX80_ _C/E-25225MAX690_M, MAX704_M, MAX80_ _M-5002500
PFI Hysteresis, PFI RisingVPFHVCC < 3.6V
MAX690_C/E, MAX704_C/E,
MAX80_ _C/E1020
MAX690_M, MAX704_M,
MAX80_ _M1025
PFI Input CurrentMAX690_C/E, MAX704_C/E, MAX80_ _C/E-25225nAMAX690_M, MAX704_M, MAX80_ _M-5002500
MR Input Threshold
VIHMAX704_/MAX806_ only0.7 x VCCVVIL0.3 x VCC
MR Pulse WidthtMRMAX704_/MAX806_ only10020ns
MR to Reset DelaytMDMAX704_/MAX806_ only60500ns
MR Pull-Up CurrentMAX704_/MAX806_ only, MR = 0V, VCC = 3V2060350µA
WDI Input ThresholdVIHMAX690_/MAX802_/MAX804_/MAX805_ only0.7 x VCCVVIL0.3 x VCC
WDI Input Current0V< VCC <
5.5V
MAX690_C/E, MAX802_C/E,
MAX804_C/E, MAX805_C/E-1+0.01+1
MAX690_M, MAX802_M,
MAX804_M, MAX805_M-10+0.01+10
Watchdog Timeout PeriodtWDVCC < 3.6VMAX690/MAX802/MAX804/
MAX805 only1.121.602.24s
WDI Pulse WidthMAX690_/MAX802_/MAX804_/MAX805_ only10020ns
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
Electrical Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
VBATT-TO-VOUT ON-RESISTANCE
vs. TEMPERATURE
MAX690 toc02
TEMPERATURE (°C)
VBATT-TO-V
OUT
ON-RESISTANCE (100–4008040120
VCC = 0V
VBATT = 3.3V
VBATT = 3V
VBATT = 2V
VBATT = 5V
SUPPLY CURRENT
vs. TEMPERATURE
MAX690-806 TOC03
TEMPERATURE (°C)
SUPPLY CURRENT (µA)100–4008040120
VCC = 5V
VCC = 3.3V
VCC = 2.5V
VBATT = 3V
PFI = GND
MR/WDI FLOATING
10,000
BATTERY SUPPLY CURRENT
vs. TEMPERATURE
MAX690 toc04
TEMPERATURE (°C)
BATTERY SUPPLY CURRENT (nA)100–4008040120
100VBATT = 3V
VBATT = 5V
VBATT = 2V
VCC = 0V
PFI = GND
RESET TIMEOUT PERIOD
vs. TEMPERATURE
MAX690 toc05
TEMPERATURE (°C)
RESET TIMEOUT PERIOD (ms)100–4008040120
VCC = 5V
VCC = 3.3V
VBATT = 3.0V
RESET-COMPARATOR PROPAGATION
DELAY vs. TEMPERATURE
MAX690 toc06
TEMPERATURE (°C)
PROPAGATION DELAY (µs)100–4008040120
VBATT = 3.0V
100mV OVERDRIVE
PFI THRESHOLD
vs. TEMPERATURE
MAX690 toc07
PFI THRESHOLD (V)100–4008040120
VCC = 5V
VCC = 3.3V
VCC = 2.5V
VBATT = 3.0V
VCC-TO-VOUT ON-RESISTANCE
vs. TEMPERATURE
MAX690 toc01
TEMPERATURE (°C)
-TO-V
OUT
ON-RESISTANCE (100–4008040120
VCC = 5V
VCC = 3.3V
VCC = 2.5V
VBATT = 3.0V
NORMALIZED RESET THRESHOLD
vs. TEMPERATURE
MAX690 toc08
NORMALIZED RESET THRESHOLD (V)100–4008040120
VBATT = 3.0V
3.0V/3.3V Microprocessor
Supervisory Circuits
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
Typical Operating Characteristics
Detailed Description
Reset Output

A microprocessor’s (µP’s) reset input starts the µP in a
known state. These µP supervisory circuits assert reset
to prevent code execution errors during power-up, power-
down, brownout conditions, or a watchdog timeout.
RESET is guaranteed to be a logic low for 0V < VCC <
VRST, provided that VBATT is greater than 1V. Without a
backup battery, RESET is guaranteed valid for VCC > 1V.
Once VCC exceeds the reset threshold, an internal timer
keeps RESET low for the reset timeout period; after this
interval, RESET goes high (Figure 2).
If a brownout condition occurs (VCC dips below the reset
threshold), RESET goes low. Each time RESET is assert-
ed, it stays low for the reset timeout period. Any time VCC
goes below the reset threshold, the internal timer restarts.
The watchdog timer can also initiate a reset. See the
Watchdog Input section.
The MAX804_/MAX805_ active-high RESET output is
open drain, and the inverse of the MAX690_/MAX704_/
Reset Threshold

The MAX690T/MAX704T/MAX805T are intended for 3.3V
systems with a ±5% power-supply tolerance and a 10%
system tolerance. Except for watchdog faults, reset will
not assert as long as the power supply remains above
3.15V (3.3V - 5%). Reset is guaranteed to assert before
the power supply falls below 3.0V.
The MAX690S/MAX704S/MAX805S are designed for
3.3V ±10% power supplies. Except for watchdog faults,
they are guaranteed not to assert reset as long as the
supply remains above 3.0V (3.3V - 10%). Reset is
guaranteed to assert before the power supply falls below
2.85V (VCC - 14%).
The MAX690R/MAX704R/MAX805R are optimized for
monitoring 3.0V ±10% power supplies. Reset will not
occur until VCC falls below 2.7V (3.0V - 10%), but is
guaranteed to occur before the supply falls below 2.59V
(3.0V - 14%).
The MAX802R/S/T, MAX804R/S/T, and MAX806R/S/T are
respectively similar to the MAX690R/S/T, MAX805R/S/T,
and MAX704R/S/T, but with tightened reset and power-fail
PIN
NAMEFUNCTIONMAX690
MAX802
MAX704
MAX806
MAX804
MAX805
11VOUT
Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT is
connected to VCC through a p-channel MOSFET switch. When VCC falls below VSW and
VBATT, VBATT connects to VOUT. Connect to VCC if no battery is used.22VCCMain Supply Input33GNDGround44PFIPower-Fail Input. When PFI is less than VPFT or when VCC falls below VSW, PFO goes
low; otherwise, PFO remains high. Connect to ground if unused.55PFOPower-Fail Output. When PFI is less than VPFT, or VCC falls below VSW, PFO goes low;
otherwise, PFO remains high. Leave open if unused.—6WDI
Watchdog Input. If WDI remains high or low for 1.6s, the internal watchdog timer runs out
and reset is triggered. The internal watchdog timer clears while reset is asserted or when
WDI sees a rising or falling edge. The watchdog function cannot be disabled.6—MR
Manual Reset Input. A logic low on MR asserts reset. Reset remains asserted as long as
MR is low and for 200ms after MR returns high. This active-low input has an internal
70µA pullup current. It can be driven from a TTL or CMOS logic line, or shorted to ground
with a switch. Leave open if unused.7—RESET
Active-Low Reset Output. Pulses low for 200ms when triggered, and stays low whenever
VCC is below the reset threshold or when MR is a logic low. It remains low for 200ms
after either VCC rises above the reset threshold, the watchdog triggers a reset, or MR
goes from low to high.—7RESETActive-High, Open-Drain Reset Output is the inverse of RESET.88VBATT
Backup-Battery Input. When VCC falls below VSW and VBATT, VOUT switches from VCC
to VBATT. When VCC rises above the reset threshold, VOUT reconnects to VCC. VBATT
may exceed VCC. Connect to VCC if no battery is used.
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
Pin Description
Watchdog Input (MAX690_/802_/804_/805_)
The watchdog circuit monitors the µP’s activity. If the µP
does not toggle the watchdog input (WDI) within 1.6sec,
a reset pulse is triggered. The internal 1.6sec timer is
cleared by either a reset pulse or by a transition (low-to-
high or high-to-low) at WDI. If WDI is tied high or low, a
RESET pulse is triggered every 1.8sec (tWD plus tRS).
As long as reset is asserted, the timer remains cleared
and does not count. As soon as reset is deasserted, the
timer starts counting. Unlike the 5V MAX690 family, the
watchdog function cannot be disabled.
Power-Fail Comparator

The PFI input is compared to an internal reference. If
PFI is less than VPFT, PFO goes low. The power-fail
comparator is intended for use as an undervoltage
detector to signal a failing power supply. However,
the comparator does not need to be dedicated to this
function because it is completely separate from the rest
of the circuitry.
The power-fail comparator turns off and PFO goes low
when VCC falls below VSW on power-down. The power-
fail comparator turns on as VCC crosses VSW on power-
up. If the comparator is not used, connect PFI to ground
and leave PFO unconnected. PFO can be connected to
MR on the MAX704_/MAX806_ so that a low voltage on
PFI will generate a reset (Figure 5b).
Figure 1. Block DiagramFigure 2. Timing Diagram
VBATT
RESET
(RESET)WDI
VCC
BATTERY
SWITCHOVER
COMPARATOR
RESET
COMPARATOR
RESET
GENERATOR
WATCHDOG
TIMER
BATTERY
SWITCHOVER
CIRCUITRY
MAX690T/S/R
MAX704T/S/R
MAX802T/S/R
MAX804T/S/R
MAX805T/S/R
MAX806T/S/R

PFO
VOUT
PFI
VPFT
1.237V
1.237V*
POWER-FAIL
COMPARATOR
* MAX690T/S/R, MAX802T/S/R, MAX804T/S/R, MAX805T/S/R ONLY
** MAX704T/S/R, MAX806T/S/R ONLY
( ) MAX804T/S/R, MAX805T/S/R ONLY
VBATT = 3.6V
3.0V OR 3.3V
VSWtWP
RESET
PFO
VCC
( ) MAX804T/S/R, MAX805T/S/R ONLY, RESET EXTERNALLY PULLED UP TO VCC
VOUT
VSW
(RESET)
3.0V OR 3.3V
3.0V OR 3.3V
VRST
VBATT = PFI = 3.6V
IOUT = 0mA
MAX690T/S/R, MAX704T/S/R, MAX802T/S/R, MAX804−MAX806T/S/R
3.0V/3.3V Microprocessor
Supervisory Circuits
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