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19-4333; Rev 3; 9/93
Microprocessor Supervisory Circuits
__________________General Description
The MAX690A/MAX692A/MAX802L/MAX802M/MAX805L reduce the complexity and number of components required for power-supply monitoring and battery-control functions in microprocessor (P) 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 P, or other low-power logic. 3) A reset pulse if the optional watchdog timer has not been toggled within 1.6sec. 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.
___________________________Features
o Precision Supply-Voltage Monitor: 4.65V for MAX690A/MAX802L/MAX805L 4.40V for MAX692A/MAX802M o Reset Time Delay - 200ms o Watchdog Timer - 1.6sec Timeout o Battery-Backup Power Switching o 200A Quiescent Supply Current o 50nA Quiescent Supply Current in BatteryBackup Mode o Voltage Monitor for Power-Fail or Low-Battery Warning o Power-Fail Accuracy Guaranteed to 2% (MAX802L/M) o Guaranteed RESET Assertion to VCC = 1V o 8-Pin SO and DIP Packages
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
______________Ordering Information
PART MAX690ACPA MAX690ACSA MAX690AC/D MAX690AEPA MAX690AESA MAX690AMJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP**
_______________________Applications
Battery-Powered Computers and Controllers Intelligent Instruments Automotive Systems Critical P Power Monitoring
Ordering Information continued on last page. * Dice are specified at TA = +25C **Contact factory for availability and processing to MIL-STD-883.
_________________Pin Configurations
TOP VIEW
__________Typical Operating Circuit
UNREGULATED DC REGULATED +5V O.1F VCC VCC PFI R2 3.6V LITHIUM BATTERY RESET PFO RESET NMI P V CC V OUT 1 2 8 VBATT RESET (RESET) WDI PFO
R1
GND 3 PFI 4
WDI VBATT VOUT GND
I/O LINE GND BUS VCC CMOS RAM GND
MAX690A MAX692A MAX802L MAX802M MAX805L
DIP/SO
7 6 5
MAX690A MAX802L
( ) ARE FOR MAX805L ONLY.
________________________________________________________________ Maxim Integrated Products
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Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND) VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.0V All Other Inputs (Note 1) . . . . . . . . . . . . . . . . -0.3V to (VCC + 0.3V) Input Current VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200mA VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50mA GND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA Output Current VOUT . . . . . . . . . . . . . . . . . . . Short-Circuit Protected for up to 10sec All Other Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20mA Rate of Rise, VCC, VBATT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100V/s Continuous Power Dissipation Plastic DIP (derate 9.09mW/C above +70C) . . . . . . . . 727mW SO (derate 5.88mW/C above +70C) . . . . . . . . . . . . . . . . 471mW CERDIP (derate 8.00mW/C above +70C) . . . . . . . . . . . 640mW Operating Temperature Ranges: MAX69_AC_ _, MAX80_ _ C_ _ . . . . . . . . . . . . . . . . . . 0C to +70C MAX69_AE_ _, MAX80_ _ E_ _ . . . . . . . . . . . . . . . . -40C to +85C MAX69_AMJA, MAX805LMJA. . . . . . . . . . . . . . . . -55C to +125C Storage Temperature Range . . . . . . . . . . . . . . . . . . -65C to +160C Lead Temperature (soldering, 10sec) . . . . . . . . . . . . . . . . . . +300C
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.
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
(V CC = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, V CC = 4.5V to 5.5V for MAX692A/MAX802M, V BATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER Operating Voltage Range, VCC, VBATT (Note 2) Supply Current (Excluding IOUT) ISUPPLY in Battery-Backup Mode (Excluding IOUT) VBATT Standby Current (Note 3) VOUT Output VOUT in Battery-Backup Mode Battery Switch Threshold, VCC to VBATT Battery Switchover Hysteresis MAX690A, MAX802L, MAX805L Reset Threshold VRT MAX692A, MAX802M MAX802L, TA = +25C, VCC falling MAX802M, TA = +25C, VCC falling Reset Threshold Hysteresis Reset Pulse Width tRS ISOURCE = 800A ISINK = 3.2mA RESET Output Voltage MAX69_AC, MAX802_C, VCC = 1.0V ISINK = 50A MAX69_AE/M, MAX802_E, VCC = 1.2V, ISINK = 100A 2 _______________________________________________________________________________________ 140 VCC - 1.5 4.50 4.25 4.55 4.30 40 200 280 0.4 0.3 0.3 V ISUPPLY SYMBOL CONDITIONS MAX69_AC, MAX802_C MAX805LC MAX69_AE/M, MAX80_ _E MAX69_AC, MAX802_C MAX69_AE/M, MAX802_E, MAX805LE/M TA = +25C VCC = 0V, VBATT = 2.8V TA = TMIN to TMAX 5.5V > VCC> VBATT +0.2V IOUT = 5mA IOUT = 50mA IOUT = 250A, VCC < VBATT - 0.2V VCC < VRT Power-up Power-down TA = +25C TA = TMIN to TMAX -0.1 MIN 1.0 1.1 1.2 200 200 0.05 TYP MAX 5.5 5.5 5.5 350 500 1.0 5.0 0.02 -1.0 0.02 VCC - 0.05 VCC - 0.025 VCC - 0.5 VCC - 0.25 20 -20 40 4.65 4.40 4.75 4.50 4.70 4.45 mV ms V VBATT - 0.1 VBATT - 0.02 A A A V V mV mV UNITS V
Microprocessor Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(V CC = 4.75V to 5.5V for MAX690A/MAX802L/MAX805L, V CC = 4.5V to 5.5V for MAX692A/MAX802M, V BATT = 2.8V, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER SYMBOL CONDITIONS MAX805LC, ISOURCE = 4A, VCC = 1.1V RESET Output Voltage MAX805LE/M, ISOURCE = 4A, VCC = 1.2V MAX805L, ISOURCE = 800A MAX805L, ISINK = 3.2mA Watchdog Timeout WDI Pulse Width WDI Input Threshold (Note 4) WDI Input Current PFI Input Threshold PFI Input Current PFO Output Voltage ISOURCE = 800A ISINK = 3.2mA tWD tWP VIL = 0.4V, VIH = (0.8) (VCC) VCC = 5V WDI = VCC WDI = 0V MAX69_A, MAX805L, VCC = 5V MAX802_C/E, VCC = 5V -150 1.20 1.225 -25 VCC - 1.5 Logic low Logic high 3.5 50 -50 1.25 1.250 0.01 1.30 1.275 25 0.4 150 1.00 50 0.8 1.60 MIN 0.8 0.9 VCC - 1.5 0.4 2.25 sec ns V A V nA V V TYP MAX UNITS
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
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 50k.
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Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
__________________________________________Typical Operating Characteristics
OUTPUT VOLTAGE vs. LOAD CURRENT
5.00 4.95 VCC = +5V VBATT = +2.8V TA = +25C VOUT (V) 2.80 2.78
OUTPUT VOLTAGE vs. LOAD CURRENT
VCC = 0V VBATT = +2.8V TA = +25C
MAX690A RESET OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
+5V VBATT = OV TA = +25C VCC 1V/div
VOUT (V)
4.90
2.76 0V 2.74 SLOPE = 80 2.72 0V 0 0.2 0.4 0.6 0.8 1.0 500ms/div IOUT (mA) RESET VCC VCC RESET GND 2k 1V/div RESET 330pF +5V
4.85 SLOPE = 5 4.80
4.75 0 10 20 30 40 50 IOUT (mA)
2.70
MAX690A RESET RESPONSE TIME
+5V VCC TA = +25C +5V VCC RESET VCC RESET GND 1V/div +5V +4V PFO PFI
POWER-FAIL COMPARATOR RESPONSE TIME
PFI +5V PFO 30pF +1.25V +1.30V PFI 0V VCC = +5V TA = +25C +1.2V 400ns/div +0V 0V 1k PFO
POWER-FAIL COMPARATOR RESPONSE TIME
+5V PFO 30pF +1.25V 1k VCC = +5V TA = +25C +3V
10k RESET 30pF
+1.3V PFI +1.20V 400ns/div
2s/div
MAX805L RESET OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
+5V VCC 1V/div +5V VCC
MAX805L RESET RESPONSE TIME
+4V VCC RESET GND
0V RESET
VCC VBATT RESET GND
+5V
10k 330 pF
0V
10k
330pF +4V
1V/div 0V 500ms/div 2s/div
0V
4
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Microprocessor Supervisory Circuits
______________________________________________________________Pin Description
PIN MAX690A/MAX692A MAX802L/MAX802M MAX805L NAME FUNCTION
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
1
1
VOUT
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. +5V Supply Input Ground Power-Fail Comparator Input. When PFI is less than 1.25V, PFO goes low. Connect PFI to GND or VCC when not used. Power-Fail Output. When PFI is less than 1.25V, PFO goes low; otherwise PFO stays high. 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 floating 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. 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.
2 3 4
2 3 4
VCC GND PFI
5
5
PFO
6
6
WDI
7
RESET
-
7
RESET
Active-High Reset Output is the inverse of RESET. When RESET is asserted, the RESET output voltage = VCC or VBATT, whichever is higher.
8
8
VBATT
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.
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Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
VBATT BATTERY-SWITCHOVER CIRCUITRY +5V VOUT VCC 0V VOUT 0V +5V RESET 0V +5V (RESET) 3.0V 0V 0.8V PFI tRS
VCC RESET (RESET)
RESET GENERATOR 3.5V 1.25V
3.0V
WDI
WATCHDOG TIMER
MAX690A MAX692A MAX802L MAX802M MAX805L
+5V PFO PFO 0V
1.25V ( ) ARE FOR MAX805L ONLY. GND ( ) ARE FOR MAX805L ONLY. VBATT = PFI = 3.0V IOUT = 0mA
Figure 1. Block Diagram
Figure 2. Timing Diagram
_______________Detailed Description
Reset Output
A microprocessor's (P's) reset input starts the P in a known state. When the P 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 powerdown, 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, RESET pulses low. As long as RESET is assert6
ed, the 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 1.8sec (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 Ps, such as Intel's 80C51, require an active-high reset pulse.
Watchdog Input
The watchdog circuit monitors the P's activity. If the P 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 Comparator
The 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 detector to signal a failing power supply; it
_______________________________________________________________________________________
Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
VBATT VCC +5V
SW1
SW2 D1 D2
SW3
SW4
VCC
VOUT
TO STATIC RAM
SUBSTRATE
MAX690A MAX802L MAX805L MAX692A MAX802M
VOUT CONDITION VCC > Reset Threshold VCC < Reset Threshold and VCC > VBATT VCC < Reset Threshold and VCC < VBATT
D3 + 0.1F
MAX690A MAX802L VBATT MAX805L RESET (RESET)
TO P
GND SW3/SW4 Closed ( ) ARE FOR MAX805L ONLY. Open Closed Closed Open
SW1/SW2 Open
RESET THRESHOLD = 4.65V IN MAX690A/MAX802L/MAX805L. RESET THRESHOLD = 4.4V IN MAX692A/MAX802M
Figure 4. Using a SuperCap as a Backup Power Source with a MAX690A/MAX802L/MAX805L and a +5V 5% Supply
Figure 3. Backup-Battery Switchover Block Diagram
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
Table 1. Input and Output Status in Battery-Backup Mode SIGNAL VCC VOUT STATUS Disconnected from VOUT Connected to VBATT through an internal 80 PMOS switch Connected to VOUT. Current drawn from the battery is less than 1A, as long as VCC < VBATT - 1V. Power-fail comparator is disabled. Logic low Logic low Logic high (MAX805L only) Watchdog timer is disabled
need not be dedicated to this function though, as it is completely separate from the rest of the circuitry. The external voltage 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 P 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 Switchover
In the event of a brownout or power failure, it may be necessary to preserve the contents of RAM. With a backup 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 5 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 80 switch) only when VCC is below the reset threshold and VBATT is greater
VBATT
PFI PFO RESET RESET WDI
_______________________________________________________________________________________
7
Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
+5V VIN +5V
R1 VCC VOUT TO STATIC RAM PFI RESET TO P R2 + 100k 0.1F GND TO P R3 C1* PFO
VCC
MAX692A MAX802M
VBATT
MAX690 MAX692A MAX802L MAX802M MAX805L
GND
*OPTIONAL +5V
Figure 5. Using a SuperCapTM as a Backup Power Source with the MAX692A/MAX802M and a +5V 10% Supply
PFO 0V 0V VL VH
VBATT is 0.6V or greater than VCC. When VBATT connects to VOUT, backup mode is activated and the internal circuitry is powered from the battery (Table 1). When VCC is just below VBATT, the current drawn from VBATT is typically 30A. When VCC drops to more than 1V below VBATT, the internal switchover comparator shuts off and the supply current falls to less than 1A.
VTRIP VIN
VTRIP = 1.25/
R2
R2 + R2

R2 || R3 VIH = 1.25/ R1 + R2 || R3
VL - 1.25 5 - 1.25 1.25 + = R1 R3 R2
__________Applications Information
Using a SuperCapTM as a Backup Power Source
SuperCaps are capacitors with extremely high capacitance values, on the order of 0.1F. Figure 4 shows a SuperCap used as a backup power source. Do not allow the SuperCap's voltage to exceed the maximum reset threshold by more than 0.6V. In Figure 4's circuit, the SuperCap rapidly charges to within a diode drop of VCC. However, after a long time, the diode leakage current will pull the SuperCap voltage up to VCC. When using a SuperCap with the MAX690A/MAX802L/MAX805L, VCC may not exceed 4.75V + 0.6V = 5.35V. Use the SuperCap circuit of Figure 5 with a MAX692A or MAX802M and a 10% supply. This circuit ensures that the SuperCap only charges to V CC 0.5V. At the maximum V CC of 5.5V, the SuperCap charges up to 5.0V, only 0.5V above the maximum reset threshold--well within the requisite 0.6V.
TMSuperCap is a trademark of Baknor Industries.
Figure 6. Adding Hysteresis to the Power-Fail Comparator
Allowable Backup Power-Source Batteries
Lithium batteries work very well as backup batteries due to very low self-discharge rates and high energy density. Single lithium batteries with open-circuit voltages of 3.0V to 3.6V are ideal. Any battery with an open-circuit voltage less than the minimum reset threshold plus 0.3V can be
Table 2. Allowable Backup-Battery Voltages (see Using a SuperCap as a Backup Power Source section for use with a SuperCap) MAXIMUM BACKUP-BATTERY PART NO. VOLTAGE (V) MAX690A/ 4.80 MAX802L/MAX805L MAX692A/ 4.55 MAX802M
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Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
connected directly to the V BATT input of the MAX690A/MAX692A/MAX802L/MAX802M/MAX805L with no additional circuitry (see the Typical Operating Circuit). However, batteries with open-circuit voltages that are greater cannot be used for backup, as current is sourced into the substrate through the diode (D1 in Figure 3) when VCC is close to the reset threshold. ICs where battery-backup mode is entered whenever VBATT gets close to VCC, an unconnected VBATT pin accumulates leakage charge and triggers RESET/RESET in error.
Adding Hysteresis to the Power-Fail Comparator
Hysteresis adds a noise margin to the power-fail comparator and prevents repeated triggering of PFO when VIN is close to its trip point. Figure 6 shows how to add hysteresis to the power-fail comparator. Select the ratio of R1 and R2 such that PFI sees 1.25V when VIN falls to its trip point (VTRIP). R3 adds the hysteresis. It will typically be an order of magnitude greater than R1 or R 2 (about 10 times either R 1 or R 2). The current through R1 and R2 should be at least 1A to ensure that the 25nA (max) PFI input current does not shift the trip point. R3 should be larger than 10k so it does not load down the PFO pin. Capacitor C1 adds additional noise rejection.
Operation Without a Backup Power Source
If a backup power source is not used, ground VBATT and connect VOUT to VCC. Since there is no need to switch over to any backup power source, VOUT does not need to be switched. A direct connection to VCC eliminates any voltage drops across the switch which may push VOUT below VCC.
Replacing the Backup Battery
The backup battery can be removed while VCC remains valid, without danger of triggering RESET/RESET. As long as VCC stays above the reset threshold, batterybackup mode cannot be entered. In other switchover
+5V
Monitoring a Negative Voltage
The power-fail comparator can be used to monitor a negative supply rail using the circuit of Figure 7. When the negative rail is good (a negative voltage of large magnitude), PFO is low. When the negative rail is degraded (a negative voltage of lesser magnitude), PFO goes high. This circuit's accuracy is affected by the PFI threshold tolerance, the VCC line, and the resistors.
R1
VCC
PFI
R2
MAX690A MAX692A MAX802L MAX802M MAX805L
PFO
Interfacing to Ps with Bidirectional Reset Pins
Ps with bidirectional reset pins, such as the Motorola 68HC11 series, can contend with the MAX690A/MAX692A/MAX802L/MAX802M RESET output. If, for example, the RESET output is driven high and the P wants to pull it low, indeterminate logic levels may result. To correct this, connect a 4.7k resistor between the RESET output and the P reset I/O, as in Figure 8. Buffer the RESET output to other system components
0V
GND V-
+5V PFO 0V VTRIP V-
= NOTE:1 VTRIP IS NEGATIVE R R2
5 - 1.25
1.25 - VTRIP
Figure 7. Monitoring a Negative Voltage
_______________________________________________________________________________________ 9
Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
BUFFERED RESET TO OTHER SYSTEM COMPONENTS
VCC
VCC
MAX690A MAX692A MAX802L RESET MAX802M
GND
4.7k RESET
GND
Figure 8. Interfacing to Ps with Bidirectional Reset I/O
10
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Microprocessor Supervisory Circuits
________________________P Supervisory Circuits
Part Number
MAX690A/692A MAX691A/693A MAX696 MAX697 MAX700 MAX703/704 MAX705/706 MAX706P MAX706R/S/T MAX707/708 MAX708R/S/T MAX709L/M/ R/S/T MAX791 MAX792L/M/ R/S/T MAX800L/M MAX802L/M MAX805L MAX813L MAX820L/M/ R/S/T MAX1232 MAX1259
MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
Minimum Nominal Reset Reset Pulse Threshold Width (V) (ms)
4.65/4.40 4.65/4.40 Adj. Adj. 4.65/adj. 4.65/4.40 4.65/4.40 2.63 2.63/2.93/ 3.08 4.65/4.40 2.63/2.93/ 3.08 140 140/adj. 35/adj. 35/adj. 200 140 140 140 140 140 140
Nominal Watchdog Timeout Backup- CE Period Battery Write (sec) Switch Protect
1.6 1.6/adj. 1.6/adj. 1.6/adj. 1.6 1.6 1.6 1 1 1.6/adj. 1.6 1.6 1.6 1 0.15/0.60/1.2 /10ns /10ns /10ns /10ns /10ns
PowerFail Comparator
Manual- Watch- LowReset dog Line Input Output Output
Active- BatteryHigh On Reset Output
4.65/4.40/ 140 2.63/2.93/3.08 4.65 140 4.65/4.40/ 140 2.63/2.93/3.08 4.60/4.40 4.60/4.40 4.65 4.65 140 140 140 140
/2% /2%
4.65/4.40/ 140 2.63/2.93/3.08 4.37/4.62 250 -
/2%
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11
Microprocessor Supervisory Circuits MAX690A/MAX692A/MAX802L/MAX802M/MAX805L
__Ordering Information (continued)
PART MAX692ACPA MAX692ACSA MAX692AC/D MAX692AEPA MAX692AESA MAX692AMJA MAX802LCPA MAX802LCSA MAX802LEPA MAX802LESA MAX802MCPA MAX802MCSA MAX802MEPA MAX802MESA MAX805LCPA MAX805LCSA MAX805LC/D MAX805LEPA MAX805LESA MAX805LMJA TEMP. RANGE 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 0C to +70C 0C to +70C -40C to +85C -40C to +85C -55C to +125C PIN-PACKAGE 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP** 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO 8 Plastic DIP 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP**
0.078" (1.98mm) PFI PFO GND RESET (RESET) 0.061" WDI (1.55mm)
____________________Chip Topography
V CC V OUT V BATT
( ) ARE FOR MAX805L ONLY. TRANSISTOR COUNT: 573; SUBSTRATE MUST BE LEFT UNCONNECTED.
* Dice are specified at TA = +25C. **Contact factory for availability and processing to MIL-STD-883.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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