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19-0487; Rev 1; 6/97
5-Pin Microprocessor Supervisory Circuits
_______________General Description
The MAX823/MAX824/MAX825* microprocessor (P) supervisory circuits combine reset output, watchdog, and manual-reset input functions in a 5-pin SOT23-5 package. They significantly improve system reliability and accuracy compared to separate ICs or discrete components. The MAX823/MAX824/MAX825 are specifically designed to ignore fast transients on VCC. Five preprogrammed reset threshold voltages are available, designated by the following package suffixes: L = 4.63V, M = 4.38V, T = 3.08V, S = 2.93V, and R = 2.63V. All three devices have an active-low reset output, which is guaranteed to be in the correct state for VCC down to 1V. The MAX824/MAX825 also have an active-high reset output. The following Selector Guide explains the functions offered in this series of parts.
____________________________Features
o Precision Monitoring of +3V, +3.3V, and +5V Power Supplies o Operating Current: 10A (MAX823L/M) 3A (MAX825T/S/R) o Fully Specified Over Temperature o 140ms Min Power-On Reset o Guaranteed RESET Valid to VCC = 1V o Power-Supply Transient Immunity o Watchdog Timer with 1.6sec Timeout (MAX823/MAX824) o Manual-Reset Input (MAX823/MAX825) o No External Components
MAX823/MAX824/MAX825
________________________Applications
Battery-Powered Computers and Controllers Embedded Controllers Intelligent Instruments Automotive Systems Critical P Monitoring Portable/Battery-Powered Equipment
______________Ordering Information
PART MAX823_EUK MAX824_EUK MAX825_EUK TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 5 SOT23-5 5 SOT23-5 5 SOT23-5
Insert the desired suffix letter (from the table below) into the blank to complete the part number. RESET THRESHOLD (V) 4.63 4.38 3.08 2.93 2.63
_____________________Selector Guide
SUFFIX FUNCTION Active-Low Reset Active-High Reset Watchdog Input Manual-Reset Input -- -- -- MAX823 MAX824 MAX825 L M T S R
Typical Operating Circuit appears at end of data sheet. Marking Information appears at end of data sheet.
__________________________________________________________Pin Configurations
TOP VIEW
RESET 1 5 VCC RESET 1 5 VCC RESET 1 5 VCC
GND 2
MAX823
GND 2
MAX824
GND 2
MAX825
MR 3
4
WDI
RESET 3
4 WDI
RESET 3
4
MR
SOT23-5
SOT23-5
SOT23-5
*Patents Pending
________________________________________________________________ Maxim Integrated Products 1
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5-Pin Microprocessor Supervisory Circuits MAX823/MAX824/MAX825
ABSOLUTE MAXIMUM RATINGS
VCC ........................................................................-0.3V to +6.0V All Other Pins..............................................-0.3V to (VCC + 0.3V) Input Current, All Pins Except RESET and RESET..............20mA Output Current, RESET, RESET ..........................................20mA Rate of Rise, VCC ............................................................100V/s Continuous Power Dissipation (TA = +70C) SOT23-5 (derate 7.1mW/C above +70C)...................571mW Operating Temperature Range MAX82_EUK .....................................................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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 = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Operating Voltage Range SYMBOL VCC CONDITIONS TA = 0C to +70C TA = -40C to +85C WDI and MR unconnected MAX823L/M, MAX824L/M MAX823T/S/R, MAX824T/S/R MAX825L/M MAX825T/S/R TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C TA = +25C TA = -40C to +85C 4.56 4.50 4.31 4.25 3.04 3.00 2.89 2.85 2.59 2.55 10 5 40 tRP MAX82_L/M MAX82_T/S/R 140 140 200 200 280 280 2.63 2.93 3.08 4.38 MIN 1.0 1.2 10 5 4.5 3 4.63 24 12 12 8 4.70 4.75 4.45 4.50 3.11 3.15 2.96 3.00 2.66 2.70 mV ppm/C ms V A TYP MAX 5.5 UNITS V
Supply Current
ISUPPLY
MR unconnected MAX82_L MAX82_M Reset Threshold VRST MAX82_T MAX82_S MAX82_R Reset Threshold Hysteresis Reset Threshold Temperature Coefficient Reset Timeout Period MAX82_L/M MAX82_T/S/R
2
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.5V for MAX82_L, VCC = +4.5V to +5.5V for MAX82_M, VCC = +3.15V to +3.6V for MAX82_T, VCC = +3V to +3.6V for MAX82_S, VCC = +2.7V to +3.6V for MAX82_R, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER SYMBOL CONDITIONS MAX82_L/M, VCC = VRST max, ISOURCE = 120A MAX82_T/S/R, VCC = VRST max, ISOURCE = 30A MAX82_L/M, VCC = VRST min, ISINK = 3.2mA MAX82_T/S/R, VCC = VRST min, ISINK = 1.2mA TA = 0C to +70C, VCC = 1V, VCC falling, ISINK = 50A TA = -40C to +85C, VCC = 1.2V, VCC falling, VBATT = 0V, ISINK = 100A RESET Output Short-Circuit Current (Note 2) ISOURCE VOH RESET Output Voltage MAX82_L/M, RESET = 0V, VCC = 5.5V MAX82_T/S/R, RESET = 0V, VCC = 3.6V VCC > 1.8V, ISOURCE = 150A MAX824L/M, MAX825L/M, VCC = VRST max, ISINK = 3.2mA MAX824T/S/R, MAX825T/S/R, VCC = VRST max, ISINK = 1.2mA VRST - VCC = 100mV tWD tWDI VIL VIH VIL = 0.4V, VIH = 0.8VCC VCC = 5V WDI = VCC, time average WDI = 0V, time average VIL VIH 1.0 100 500 35 52 75 -20 0.3VCC 0.7VCC 1.12 50 0.3VCC 0.7VCC 120 -15 160 20 1.60 2.40 0.8VCC 0.4 0.3 s sec ns V A V MIN VCC - 1.5 0.8VCC 0.4 V 0.3 0.3 0.3 800 400 A TYP MAX UNITS
MAX823/MAX824/MAX825
VOH
RESET Output Voltage VOL
VOL
VCC to RESET Delay WATCHDOG INPUT (MAX823/MAX824) Watchdog Timeout Period WDI Pulse Width WDI Input Threshold (Note 3) WDI Input Current (Note 4) MANUAL-RESET INPUT (MAX823/MAX825) MR Input Threshold MR Pulse Width MR Noise Immunity (pulse width with no reset) MR to Reset Delay MR Pull-Up Resistance (internal) Note 1: Note 2: Note 3: Note 4:
V s ns ns k
Over-temperature limits are guaranteed by design and not production tested. The RESET short-circuit current is the maximum pull-up current when RESET is driven low by a P bidirectional reset pin. WDI is internally serviced within the watchdog period if WDI is left unconnected. The WDI input current is specified as the average input current when the WDI input is driven high or low. The WDI input is designed to drive a three-stated-output device with a 10A maximum leakage current and a maximum capacitive load of 200pF. This output device must be able to source and sink at least 200A when active. _______________________________________________________________________________________ 3
5-Pin Microprocessor Supervisory Circuits MAX823/MAX824/MAX825
__________________________________________Typical Operating Characteristics
(MAX823L, VCC = +5V, TA = +25C, unless otherwise noted.)
VCC SUPPLY CURRENT vs. TEMPERATURE
MAX823/4/5-01
RESET TIMEOUT PERIOD vs. TEMPERATURE
MAX823/4/5-02
RESET COMPARATOR PROPAGATION DELAY vs. TEMPERATURE
VCC FALLING PROPAGATION DELAY (s) 25 20 15 10 5 0
MAX823/4/5-03
12.5 12.0 SUPPLY CURRENT (A) 11.5 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 -40 -20 0 20 40 60 80
250 240 RESET TIMEOUT PERIOD (ms) 230 220 210 200 190 180 170 160 150
30
100
-40
-20
0
20
40
60
80
100
-40
-20
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
TEMPERATURE (C)
WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE
MAX823/4/5-04
NORMALIZED RESET THRESHOLD VOLTAGE vs. TEMPERATURE
MAX823/4/5-05
MAXIMUM VCC TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE
140 TRANSIENT DURATION (s) 120 100 80 60 40 20 RESET OCCURS ABOVE CURVE
MAX823/4/5-06
2.0 WATCHDOG TIMEOUT PERIOD (sec) 1.9 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 -40 -20 0 20 40 60 80
1.06 NORMALIZED RESET THRESHOLD (V) 1.04 1.02 1.00 0.98 0.96 0.94
160
0 -40 -20 0 20 40 60 80 100 0 20 40 60 80 100 120 140 160 180 200 TEMPERATURE (C) RESET THRESHOLD OVERDRIVE (mV), VRST - VCC
100
TEMPERATURE (C)
4
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits
______________________________________________________________Pin Description
MAX823 PIN MAX824 MAX825 NAME FUNCTION Active-Low Reset Output. Pulses low for 200ms when triggered, and remains low whenever VCC is below the reset threshold or when MR is a logic low. It remains low for 200ms after one of the following occurs: VCC rises above the reset threshold, the watchdog triggers a reset, or MR goes low to high. Ground. 0V reference for all signals. Manual-Reset Input. A logic low on MR asserts reset. Reset remains asserted as long as MR is held low and for 200ms after MR returns high. The active-low input has an internal 52k pull-up resistor. It can be driven from a CMOS-logic line or shorted to ground with a switch. Leave open or connect to V CC if unused. Active-High Reset Output. Inverse of RESET. Watchdog Input. If WDI remains either high or low for longer than the watchdog timeout period, the internal watchdog timer runs out and a reset is triggered. The internal watchdog timer clears whenever reset is asserted, or whenever WDI sees a rising or falling edge. If WDI is left unconnected or is connected to a three-stated buffer output, the watchdog feature is disabled. Supply Voltage
MAX823/MAX824/MAX825
1
1
1
RESET
2
2
2
GND
3
--
4
MR
--
3
3
RESET
4
4
--
WDI
5
5
5
VCC
VCC
MAX823 MAX824 MAX825
RESET GENERATOR VCC 1.25V RESET RESET (MAX824/MAX825 ONLY)
MR (MAX823/MAX825 ONLY) WDI (MAX823/MAX824 ONLY) WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER
GND
Figure 1. Functional Diagram
_______________________________________________________________________________________ 5
5-Pin Microprocessor Supervisory Circuits MAX823/MAX824/MAX825
_______________Detailed Description
RESET Output
A microprocessor's (P's) reset input starts the P in a known state. The MAX823/MAX824/MAX825 P supervisory circuits assert a reset to prevent code-execution errors during power-up, power-down, and brownout conditions. RESET is guaranteed to be a logic low for VCC down to 1V. Once VCC exceeds the reset threshold, an internal timer keeps RESET low for the specified reset timeout period (tRP); after this interval, RESET returns high (Figure 2). If a brownout condition occurs (VCC dips below the reset threshold), RESET goes low. Each time RESET is asserted it stays low for the reset timeout period. Any time VCC goes below the reset threshold the internal timer restarts. RESET both sources and sinks current. RESET on the MAX824/MAX825 is the inverse of RESET.
Watchdog Input (MAX823/MAX824)
In the MAX823/MAX824, the watchdog circuit monitors the P's activity. If the P does not toggle the watchdog input (WDI) within tWD (1.6sec), reset asserts. The internal 1.6sec timer is cleared by either a reset pulse or by toggling WDI, which detects pulses as short as 50ns. While reset is asserted, the timer remains cleared and does not count. As soon as reset is released, the timer starts counting (Figure 3). Disable the watchdog function by leaving WDI unconnected or by three-stating the driver connected to WDI. The watchdog input is internally driven low during the first 7/8 of the watchdog timeout period and high for the last 1/8 of the watchdog timeout period. When WDI is left unconnected, this internal driver clears the 1.6sec timer every 1.4sec. When WDI is three-stated or unconnected, the maximum allowable leakage current is 10A and the maximum allowable load capacitance is 200pF.
Manual-Reset Input (MAX823/MAX825)
Many P-based products require manual-reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. On the MAX823/ MAX825, a logic low on MR asserts reset. Reset remains asserted while MR is low, and for tRP (200ms nominal) after it returns high. MR has an internal 52k pull-up resistor, so it can be left open if not used. This input can be driven with CMOS-logic levels or with open-drain/ collector outputs. Connect a normally open momentary switch from MR to GND to create a manual-reset function; external debounce circuitry is not required. If MR is driven from long cables or the device is used in a noisy environment, connect a 0.1F capacitor from MR to GND to provide additional noise immunity.
__________Applications Information
Watchdog Input Current
The MAX823/MAX824 WDI inputs are internally driven through a buffer and series resistor from the watchdog counter (Figure 1). When WDI is left unconnected, the watchdog timer is serviced within the watchdog timeout period by a low-high-low pulse from the counter chain. For minimum watchdog input current (minimum overall power consumption), leave WDI low for the majority of the watchdog timeout period, pulsing it low-high-low once within the first 7/8 of the watchdog timeout period to reset the watchdog timer. If WDI is externally driven high for the majority of the timeout period, up to 160A can flow into WDI.
VCC 1V VRST VRST 1V
VCC tRST RESET*
RESET
tRP
tRD
tRP
tWD
tRP
RESET GND
tRP
tRD
WDI
*RESET ON THE MAX824/MAX825 IS THE INVERSE OF RESET.
Figure 2. Reset Timing Diagram
6
Figure 3. MAX823/MAX824 Watchdog Timing Relationship
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits
Interfacing to Ps with Bidirectional Reset Pins
The RESET output maximum pull-up current is 800A for L/M versions (400A for T/S/R versions). This allows Ps with bidirectional resets, such as the 68HC11, to force RESET low when the MAX823/MAX824/MAX825 are pulling RESET high (Figure 4). An optional 0.1F bypass capacitor mounted close to VCC provides additional transient immunity.
MAX823/MAX824/MAX825
Watchdog Software Considerations (MAX823/MAX824)
One way to help the watchdog timer monitor software execution more closely is to set and reset the watchdog input at different points in the program, rather than pulsing the watchdog input high-low-high or low-highlow. This technique avoids a stuck loop, in which the watchdog timer would continue to be reset inside the loop, keeping the watchdog from timing out. Figure 5 shows an example of a flow diagram where the I/O driving the watchdog input is set high at the beginning of the program, set low at the beginning of every subroutine or loop, then set high again when the program returns to the beginning. If the program should hang in any subroutine, the problem would quickly be corrected, since the I/O is continually set low and the watchdog timer is allowed to time out, causing a reset or interrupt to be issued. As described in the Watchdog Input Current section, this scheme results in higher time average WDI input current than does leaving WDI low for the majority of the timeout period and periodically pulsing it low-high-low.
Negative-Going VCC Transients
These supervisors are relatively immune to shortduration, negative-going VCC transients (glitches), which usually do not require the entire system to shut down. Resets are issued to the P during power-up, powerdown, and brownout conditions. The Typical Operating Characteristics show a graph of the MAX823L's Maximum VCC Transient Duration vs. Reset Threshold Overdrive, for which reset pulses are not generated. The graph was produced using negative-going VCC pulses, starting at 5V and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negative-going VCC transient can typically have without triggering a reset pulse. As the amplitude of the transient increases (i.e., goes farther below the reset threshold), the maximum allowable pulse width decreases. Typically, a VCC transient that goes 100mV below the reset threshold and lasts for 15s or less will not trigger a reset pulse.
START
VCC VCC
SET WDI HIGH PROGRAM CODE
MAX823 MAX824 MAX825
RESET GENERATOR
ISOURCE MAX = 800A L, M 400A T, S, R
VCC
RESET
P
SUBROUTINE OR PROGRAM LOOP SET WDI LOW
GND GND RETURN
Figure 4. Interfacing to Ps with Bidirectional Resets
Figure 5. Watchdog Flow Diagram
7
_______________________________________________________________________________________
5-Pin Microprocessor Supervisory Circuits MAX823/MAX824/MAX825
__________Typical Operating Circuit ___________________Chip Information
TRANSISTOR COUNT: 607
VCC VCC VCC RESET RESET
______________Package Information
MARKING INFORMATION (TOP) XXXX
AAAI = MAX823L AAAJ = MAX823M AAAK = MAX823T AAAL = MAX823S AAAM = MAX823R AAAN = MAX824L AAAO = MAX824M AAAP = MAX824T AAAQ = MAX824S AAAR = MAX824R AAAS = MAX825L AAAT = MAX825M AAAU = MAX825T AAAV = MAX825S AAAW = MAX825R
MAX823
WDI MANUAL RESET MR I/O
P
GND
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.
8 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-377-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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