MAX705–MAX708/MAX813L
Low-Cost, µP Supervisory Circuits
________________________________________________________________Maxim Integrated Products 1
_________________Pin Configurations
__________Typical Operating Circuit
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19-4334; Rev. 5; 9/95
_______________General Description
The 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 signifi-cantly improve system reliability and accuracy com-pared 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 1.6seconds.
3)A 1.25V threshold detector for power-fail warning,low-battery detection, or for monitoring a power sup-ply 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 Automotive Systems
Critical µP Power Monitoring
___________________________Features
o µMAX Package: Smallest 8-Pin SO o Guaranteed RESET Valid at V CC = 1V o Precision Supply-Voltage Monitor
4.65V in MAX705/MAX707/MAX813L 4.40V in MAX706/MAX708o 200ms Reset Pulse Width
timeout of 5000ms exceededo Debounced TTL/CMOS-Compatible Manual-Reset Input
o Independent Watchdog Timer—1.6sec Timeout (MAX705/MAX706)o Active-High Reset Output (MAX707/MAX708/MAX813L)
o Voltage Monitor for Power-Fail or Low-Battery Warning
______________Ordering Information
Ordering Information continued at end of data sheet.*Dice are specified at T A = +25°C.
**Contact factory for availability and processing to MIL-STD-883.
M A X 705–M A X 708/M A X 813L
Low-Cost, µP Supervisory Circuits
Terminal Voltage (with respect to GND)
V CC ..............................................-0.3V to 6.0V All Other Inputs (Note 1)...............-0.3V to (V CC + 0.3V)Input Current
V CC ......................................................20mA GND ....................................................20mA Output Current (all outputs).............................20mA Continuous Power Dissipation
Plastic DIP (derate 9.09mW/°C above +70°C).......727mW
SO (derate 5.88mW/°C above +70°C)...............471mW µMAX (derate 4.10mW/°C above +70°C)............330mW CERDIP (derate 8.00mW/°C above +70°C)..........640mW Operating Temperature Ranges
MAX70_C__, MAX813LC__....................0°C to +70°C MAX70_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, 10sec)................+300°C
ELECTRICAL CHARACTERISTICS
(V CC = 4.75V to 5.5V for MAX705/MAX707/MAX813L, V CC = 4.5V to 5.5V for MAX706/MAX708, T A = T MIN to T MAX , unless otherwise noted.)
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.
ABSOLUTE MAXIMUM RATINGS
Note 1:The input voltage limits on PFI and MR can be exceeded if the input current is less than 10mA.
MAX705–MAX708/MAX813L
Low-Cost, µP Supervisory Circuits
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ELECTRICAL CHARACTERISTICS (continued)
(V CC = 4.75V to 5.5V for MAX705/MAX707/MAX813L, V CC = 4.5V to 5.5V for MAX706/MAX708, T A = T MIN to T MAX , unless otherwise noted.)
Note 2:Applies to both RESET in the MAX705-MAX708 and RESET in the MAX707/MAX708/MAX813L.
M A X 705–M A X 708/M A X 813L
Low-Cost, µP Supervisory Circuits 4_______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
MAX707/MAX708/MAX813L RESET OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
500ms/div
V CC
0V
RESET
0V
+5V
1V/div
+5V
1V/div
MAX813L
RESET RESPONSE TIME
2µs/div
+5V V CC
0V
0V
+4V
+4V
MAX705/MAX707 RESET OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
500ms/div
V CC
0V
RESET
0V
+5V
1V/div
+5V
1V/div
MAX705/MAX707 RESET RESPONSE TIME 2µs/div
V CC
+5V RESET
+5V
+4V
1V/div 0V
POWER-FAIL COMPARATOR DE-ASSERTION RESPONSE TIME
400ns/div
PFI +1.20V
PFO
0V
+3V
+1.30V
POWER-FAIL COMPARATOR ASSERTION RESPONSE TIME
400ns/div
PFI
+1.30V PFO
+5V
0V
+1.20V
1V/div
50mV/div
MAX707
RESET, RESET ASSERTION
400ns/div
0V
+5V
RESET
1V/div
+5V
0V
MAX707
400ns/div
0V +5V
RESET RESET
2V/div
+5V
0V
MAX705–MAX708/MAX813L
Low-Cost, µP Supervisory Circuits
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______________________________________________________________Pin Description
M A X 705–M A X 708/M A X 813L
_______________Detailed Description
Reset Output
A 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 execu-tion errors during power-down or brownout conditions.On power-u
p, once V CC reaches 1V, RESET is a guaran-teed logic low of 0.4V or less. As V CC rises, RESET stays low. When V CC rises above the reset threshold, an inter-nal timer releases RESET after about 200ms. RESET puls-es low whenever V CC 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 V CC falls below the reset threshold, RESET stays low and is guar-anteed to be 0.4V or less until V CC 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 V CC down to 1.1V. Some µPs,such as Intel’s 80C51, require an active-high reset pulse.
Watchdog Timer
The MAX705/MAX706/MAX813L watchdog circuit moni-tors the µP’s activity. If the µP does not toggle the watch-dog input (WDI) within 1.6sec and WDI is not three-stat-is asserted or the
WDI input is three-stated, the watchdog timer will stay cleared and will not count. As soon as reset is released and WDI is driven high or low, the timer will start counting.Pulses as short as 50ns can be detected.
Typically, WDO will be connected to the non-maskable interrupt input (NMI) of a µP. When V CC drops below will go low whether or not the watchdog timer has timed out yet. Normally this would trigger an NMI interrupt, but RESET goes low simultane-ously, and thus overrides the NMI interrupt.
If WDI is left unconnected, WDO can be used as a low-line output. Since floating WDI disables the internal timer, WDO goes low only when V CC 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 Reset
The manual-reset input (MR) allows reset to be trig-gered 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 can be used to force a watchdog timeout to generate a reset pulse in the MAX705/MAX706/MAX813L. Simply connect WDO to MR.
Low-Cost, µP Supervisory Circuits 6
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Figure 1. MAX705/MAX706/MAX813L Block Diagram Figure 2. MAX707/MAX708 Block Diagram
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