MAX690ACSA+ ,Microprocessor Supervisory CircuitsElectrical Characteristics(V = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, V = 4.5V to 5.5V for MAX6 ..
MAX690ACSA+T ,Microprocessor Supervisory CircuitsMAX690A/MAX692A/ Microprocessor Supervisory CircuitsMAX802L/MAX802M/MAX805L
MAX690AEPA ,Microprocessor Supervisory CircuitsGeneral Description _______
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MAX690ACPA+-MAX690ACSA+-MAX690ACSA+T-MAX690AEPA+-MAX690AESA+-MAX690AESA+T-MAX692ACSA+-MAX692AEPA+-MAX692AESA+-MAX692AESA+T-MAX802LCSA+-MAX802LCSA+T-MAX802LESA+-MAX805LCSA+-MAX805LEPA+-MAX805LESA+
Microprocessor Supervisory Circuits
General DescriptionThe MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
reduce the complexity and number of components
required for power-supply monitoring and battery- control functions in microprocessor (μP) systems. They
significantly improve system reliability and accuracy compared to separate ICs or discrete components.
These parts provide four functions:
1) A reset output during power-up, power-down, and brownout conditions.
2) Battery-backup switching for CMOS RAM, CMOS μP, or other low-power logic.
3) A reset pulse if the optional watchdog timer has not been toggled within 1.6s.
4) A 1.25V threshold detector for power-fail warning or low-battery detection, or to monitor a power supply other than +5V.
The parts differ in their reset-voltage threshold levels and reset outputs. The MAX690A/MAX802L/MAX805L generate a reset pulse when the supply voltage drops below 4.65V, and the MAX692A/MAX802M generate a reset below 4.40V.
The MAX802L/MAX802M guarantee power-fail accuracies to ±2%. The MAX805L is the same as the MAX690A except that RESET is provided instead of RESET.
All parts are available in 8-pin DIP and SO packages.
The MAX690A/MAX802L are pin compatible with the MAX690 and MAX694. The MAX692A/MAX802M are pin compatible with the MAX692.
Applications●Battery-Powered Computers and Controllers●Intelligent Instruments●Critical μP Power Monitoring
Features●Precision Supply Voltage Monitor: 4.65V for MAX690A/MAX802L/MAX805L 4.40V for MAX692A/MAX802M●Reset Time Delay: 200ms●Watchdog Timer: 1.6s Timeout●Battery-Backup Power Switching●200μA Quiescent Supply Current●50nA Quiescent Supply Current in Battery- Backup Mode●Voltage Monitor for Power-Fail or Low-Battery
Warning●Power-Fail Accuracy Guaranteed to ±2% (MAX802L/M)●Guaranteed RESET Assertion to VCC = 1V●8-Pin SO and DIP Packages
Ordering Information continued at end of data sheet.*Dice are specified at TA = +25°C
**Contact factory for availability and processing to MIL STD-
883. 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.
PARTTEMP RANGEPIN-PACKAGE
MAX690ACPA0°C to +70°C8 Plastic DIP
MAX690ACSA0°C to +70°C8 SO
MAX690AC/D0°C to +70°CDice*
MAX690AEPA-40°C to +85°C8 Plastic DIP
MAX690AESA-40°C to +85°C8 SO
MAX690AMJA-55°C to +125°C8 CERDIP**
VCC
VCC
NMI
I/O LINEGND
GND
BUS
CMOS
RAM
UNREGULATED
REGULATED +5V
RESET
PFO
WDI
VOUT
GND
VBATT
VCC
PFI
0.1µF
3.6V
LITHIUM
BATTERY
MAX690A
MAX802LRESET
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
Typical Operating CircuitPin Conigurations
Ordering InformationVBATT
RESET(RESET)
WDI
PFOPFI
GND
VCC
VOUT
DIP/SOTOP VIEW
MAX690A
MAX692A
MAX802L
MAX802M
MAX805L( ) ARE FOR MAX805L ONLY.
Terminal Voltage (with respect to GND) VCC ...................................................................-0.3V to +6.0V VBATT ...............................................................-0.3V to +6.0VAll Other Inputs (Note 1) ..........................-0.3V to (VCC + 0.3V)
Input Current VCC ...............................................................................200mA VBATT .............................................................................50mA GND ................................................................................20mAOutput Current VOUT ..............................Short-Circuit Protected for up to 10s All Other Outputs ............................................................20mA
Rate of Rise, VCC, VBATT ..............................................100V/μsContinuous Power Dissipation 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) ................640mWOperating Temperature Ranges: MAX69_AC_ _, MAX80_ _ C_ _ ........................0°C to +70°C MAX69_AE_ _, MAX80_ _ E_ _ ...................-40°C to +85°C MAX69_AMJA, MAX805LMJA .....................-55°C to +125°CStorage Temperature Range ............................-65°C to +160°CLead Temperature (soldering, 10s) ................................ +300°C
(VCC = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, VCC = 4.5V to 5.5V for MAX692A/MAX802M, VBATT = 2.8V, TA = TMIN to
TMAX, unless otherwise noted.)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Voltage Range, VCC, VBATT (Note 2)
MAX69_AC, MAX802_C1.05.5MAX805LC1.15.5
MAX69_AE/M, MAX80_ _E1.25.5
Supply Current (Excluding IOUT)ISUPPLYMAX69_AC, MAX802_C200350MAX69_AE/M, MAX802_E, MAX805LE/M200500
ISUPPLY in Battery-Backup Mode (Excluding IOUT)VCC = 0V, VBATT = 2.8V
TA = +25°C0.051.0µA
TA = TMIN to TMAX5.0
VBATT Standby Current (Note 3)5.5V > VCC > VBATT +0.2V
TA = +25°C-0.10.02µA
TA = TMIN to TMAX-1.00.02
VOUT Output
IOUT = 5mAVCC - 0.05VCC - 0.025V
IOUT = 50mAVCC - 0. 5VCC - 0. 25
VOUT in Battery-Backup ModeIOUT = 250μA, VCC < VBATT - 0.2VVBATT - 0.1VBATT - 0.02V
Battery Switch Threshold, VCC to VBATTVCC < VRTPower-up20mVPower-down-20
Battery Switchover Hysteresis40mV
Reset ThresholdVRT
MAX690A, MAX802L, MAX805L4.504.654.75MAX692A, MAX802M4.254.404.50
MAX802L, TA = +25°C, VCC falling4.554.70
MAX802M, TA = +25°C, VCC falling4.304.45
Reset Threshold Hysteresis40mV
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
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
Note 1: The input voltage limits on PFI and WDI may be exceeded if the current into these pins is limited to less than 10mA.
(VCC = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, VCC = 4.5V to 5.5V for MAX692A/MAX802M, VBATT = 2.8V, TA = TMIN to
TMAX, unless otherwise noted.)
Note 2: Either VCC or VBATT can go to 0V, if the other is greater than 2.0V.
Note 3: “-” = battery-charging current, “+” = battery-discharging current.
Note 4: WDI is guaranteed to be in an intermediate, non-logic level state if WDI is floating and VCC is in the operating voltage range. WDI is internally biased to 35% of VCC with an input impedance of 50kΩ.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSRESET Output Voltage
ISOURCE = 800μA
ISINK = 3.2mA0.4
MAX69_AC, MAX802_C, VCC = 1.0V
ISINK = 50μA0.3
MAX69_AE/M, MAX802_E, VCC = 1.2V, ISINK = 100μA0.3
RESET Output Voltage
MAX805LC, ISOURCE = 4μA, VCC = 1.1V0.8MAX805LE/M, ISOURCE = 4μA, VCC = 1.2V0.9
MAX805L, ISOURCE = 800μAVCC - 1.5
MAX805L, ISINK = 3.2mA0.4
Watchdog TimeouttWD1.001.602.25s
WDI Pulse WidthtWPVIL = 0.4V, VIH = (0.8) (VCC)50ns
WDI Input Threshold (Note 4)VCC = 5VLogic low0.8V
Logic high3.5
WDI Input CurrentWDI = VCC50150WDI = 0V-150-50
PFI Input ThresholdMAX69_A, MAX805L, VCC = 5V1.201.251.30VMAX802_C/E, VCC = 5V1.2251.2501.275
PFI Input Current-250.0125nA
PFO Output VoltageISOURCE = 800μAVCC - 1.5V
ISINK = 3.2mA0.4
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
Electrical Characteristics (continued)
OUTPUT VOLTAGE
vs. LOAD CURRENT
IOUT (mA)
OUT
(V)
VCC = +5V
VBATT = +2.8V
TA = +25°C
SLOPE = 5Ω
MAX690A-MAX805L toc01
MAX690A
RESET RESPONSE TIME2µs/div
VCC
+5V
RESET
+5V
+4V
1V/div
TA = +25°C
VCCVCC
GND
RESET
10k
RESET
30pF
MAX690A-MAX805L toc04
MAX805L RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE500ms/div
VCC
+5V
1V/div
RESET
+5V
1V/div
10k330
VCC
RESET
GND
VBATT
MAX690A-MAX805L toc07
MAX805L
RESET RESPONSE TIME2µs/div
VCC+4V
+4V
+5V
GND
RESET
VCC
330pF10k
MAX690A-MAX805L toc08
OUTPUT VOLTAGE
vs. LOAD CURRENT
IOUT (mA)
OUT
(V)
VCC = 0V
VBATT = +2.8V
TA = +25°C
SLOPE = 80Ω
MAX690A-MAX805L toc02
POWER-FAIL COMPARATOR
RESPONSE TIME400ns/div
PFI
+1.30V
PFO
+5V
+0V
+1.2V
+5V
PFO
30pF
+1.25V
PFI
VCC = +5V
TA = +25°C
MAX690A-MAX805L toc05
MAX690A RESET OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE500ms/div
VCC
RESET
+5V
1V/div
+5V
1V/div
TA = +25°C
VBATT = OV
VCCVCC
GND
RESET
RESET
330pF
MAX690A-MAX805L toc03
POWER-FAIL COMPARATOR
RESPONSE TIME400ns/div
PFI
+1.20V
PFO
+3V
+1.3V
VCC = +5V
TA = +25°C
+5V
PFO
30pF1k
+1.25V
PFI
MAX690A-MAX805L toc06
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
Typical Operating Characteristics
PIN
NAMEFUNCTIONMAX690A/MAX692A
MAX802L/MAX802MMAX805L1VOUT
Supply Output for CMOS RAM. When VCC is above the reset threshold, VOUT connects to VCC through a P-channel MOSFET switch. When VCC is below the reset threshold, the higher of VCC or VBATT will be connected to VOUT.2VCC+5V Supply Input3GNDGround4PFIPower-Fail Comparator Input. When PFI is less than 1.25V, PFO goes low. Connect PFI to GND or VCC when not used.5PFOPower-Fail Output. When PFI is less than 1.25V, PFO goes low;
otherwise PFO stays high.6WDI
Watchdog Input. If WDI remains high or low for 1.6sec, the internal watchdog timer runs out and reset is triggered. If WDI is left loating or connected to a high-impedance three-state buffer, the watchdog feature is disabled. The internal watchdog timer clears whenever reset is asserted, WDI is three-stated, or WDI sees a rising or falling edge.7RESET
Reset Output. Whenever RESET is triggered, it pulses low for 200ms. It stays low when VCC is below the reset threshold (4.65V in the MAX690A/MAX802L and 4.4V in the MAX692A/MAX802M) and remains low for 200ms after VCC rises above the reset threshold. A watchdog
timeout also triggers RESET.—RESETActive-High Reset Output is the inverse of RESET. When RESET is asserted, the RESET output voltage = VCC or VBATT, whichever is higher.8VBATT
Backup-Battery Input. When VCC falls below the reset threshold, VBATT will be switched to VOUT if VBATT is 20mV greater than VCC. When VCC rises to 20mV above VBATT, VOUT will be reconnected to VCC. The 40mV hysteresis prevents repeated switching if VCC falls slowly.
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
Pin Description
Detailed Description
Reset OutputA microprocessor’s (μP’s) reset input starts the μP in a known state. When the μP is in an unknown state, it should be held in reset. The MAX690A/MAX692A/
MAX802L/MAX802M 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 guaranteed to be a logic low. As VCC rises, RESET remains low. When VCC exceeds the reset threshold, an internal timer keeps RESET low for a time equal to the reset pulse width; after this interval, RESET goes high (Figure 2). If a brownout condition occurs (if VCC dips below the reset threshold), RESET is triggered. Each time RESET is triggered, it stays low for the reset pulse width interval. Any time VCC goes below the reset threshold, the internal timer restarts the pulse. If a brownout condition interrupts a previously initiated reset pulse, the reset pulse continues for another 200ms. On power-down, once VCC goes below the threshold, RESET is guaranteed to be logic low until VCC droops below 1V.
RESET is also triggered by a watchdog timeout. If a high or low is continuously applied to the WDI pin for 1.6sec,
watchdog timer remains clear. When RESET comes high, the watchdog resumes timing and must be serviced within 1.6sec. If WDI is tied high or low, a RESET pulse is triggered every 1.8s (tWD plus tRS).
The MAX805L active-high RESET output is the inverse
of the MAX690A/MAX692A/MAX802L/MAX802M 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 InputThe 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 open circuiting the WDI input. As long as reset is asserted or the WDI input is open circuited, the timer remains cleared and does not count. As soon as reset is released or WDI is driven high or low, the timer starts counting. It can detect pulses as
short as 50ns.
Power-Fail ComparatorThe PFI input is compared to an internal 1.25V reference. If PFI is less than 1.25V, PFO goes low. The power-
fail comparator is intended for use as an undervoltage
Figure 1. Block DiagramFigure 2. Timing Diagram
0.8V
WATCHDOG
TIMER
PFO
RESET
(RESET)
VOUT
RESET
GENERATOR
BATTERY-SWITCHOVER
CIRCUITRY
1.25V
3.5V
VBATT
VCC
PFI
WDI
MAX690A
MAX692A
MAX802L
MAX802M
MAX805L( ) ARE FOR MAX805L ONLY.
GND
1.25V
tRS
+5V
VCC
+5V
RESET
+5V
(RESET)
3.0V
3.0V
VOUT
+5V
PFO
VBATT = PFI = 3.0V
IOUT = 0mA( ) ARE FOR MAX805L ONLY.
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
dedicated to this function though, as it is completely separate from the rest of the circuitry. The external volt-age divider drives PFI to sense the unregulated DC input to the +5V regulator (see Typical Operating Circuit). The
voltage-divider ratio can be chosen such that the voltage at PFI falls below 1.25V just before the +5V regulator drops out. PFO then triggers an interrupt which signals the μP to prepare for power-down.
To conserve backup-battery power, the power-fail
detector comparator is turned off and PFO is forced low when VBATT connects to VOUT.
Backup-Battery SwitchoverIn the event of a brownout or power failure, it may be necessary to preserve the contents of RAM. With a back-up battery installed at VBATT, the devices automatically switch RAM to backup power when VCC fails.
As long as VCC exceeds the reset threshold, VOUT connects to VCC through a 5Ω PMOS power switch. Once VCC falls below the reset threshold, VCC or VBATT (whichever is higher) switches to VOUT. Unlike the MAX690/MAX692, the MAX690A/MAX692A/MAX802L/
MAX802M/MAX805L don’t always connect VBATT to VOUT when VBATT is greater than VCC. VBATT connects to VOUT (through an 80Ω switch) only when VCC is below
the reset threshold and VBATT is greater than VCC.
When VCC exceeds the reset threshold, it is connected to
the MAX690A/MAX692A/MAX802L/MAX802M/MAX805L substrate, regardless of the voltage applied to VBATT (Figure 3). During this time, the diode (D1) between VBATT and the substrate will conduct current from VBATT to VCC if VBATT is 0.6V or greater than VCC.
Figure 3. Backup-Battery Switchover Block Diagram
Figure 4. Using a SuperCap as a Backup Power Source with a
MAX690A/MAX802L/MAX805L and a +5V ±5% Supply
Table 1. Wiper Position and Attenuation
SIGNALSTATUSVCCDisconnected from VOUT
VOUTConnected to VBATT through an internal 80Ω PMOS switch
VBATTConnected to VOUT. Current drawn from the battery is less than 1μA, as long asVCC < VBATT - 1V.
PFIPower-fail comparator is disabled.
PFOLogic low
RESETLogic low
RESETLogic high (MAX805L only)
WDIWatchdog timer is disabled
SW1/SW2SW3/SW4CONDITIONVCC > Reset ThresholdOpenClosed
ClosedOpen
OpenClosed
VCC < Reset Threshold and
VCC > VBATT
VCC < Reset Threshold and
VCC < VBATT
RESET THRESHOLD = 4.65V IN MAX690A/MAX802L/MAX805L.
RESET THRESHOLD = 4.4V IN MAX692A/MAX802M
VOUT
SUBSTRATED2
SW2SW1SW4SW3
VBATTVCC
MAX690A
MAX692A
MAX802L
MAX802M
MAX805LVBATT
VCCVOUT
RESET
(RESET)
GND
TO STATIC RAM
TO µP
0.1F
MAX690A
MAX802L
MAX805L+5V
( ) ARE FOR MAX805L ONLY.
MAX690A/MAX692A/
MAX802L/MAX802M/
MAX805L
Microprocessor Supervisory Circuits
