19-0487; Rev 1; 6/97 5-Pin Microprocessor Supervisory Circuits ________________________Applications ____________________________Features ♦ Precision Monitoring of +3V, +3.3V, and +5V Power Supplies ♦ Operating Current: 10µA (MAX823L/M) 3µA (MAX825T/S/R) ♦ Fully Specified Over Temperature ♦ 140ms Min Power-On Reset ♦ Guaranteed RESET Valid to VCC = 1V ♦ Power-Supply Transient Immunity ♦ Watchdog Timer with 1.6sec Timeout (MAX823/MAX824) ♦ Manual-Reset Input (MAX823/MAX825) ♦ No External Components ______________Ordering Information PART† Battery-Powered Computers and Controllers Embedded Controllers Intelligent Instruments Automotive Systems Critical µP Monitoring Portable/Battery-Powered Equipment MAX823_EUK MAX824_EUK MAX825_EUK TEMP. RANGE PIN-PACKAGE -40°C to +85°C -40°C to +85°C -40°C to +85°C 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. _____________________Selector Guide FUNCTION Active-Low Reset RESET THRESHOLD (V) ✔ L 4.63 ✔ M 4.38 — ✔ T 3.08 S 2.93 R 2.63 MAX824 MAX825 ✔ ✔ ✔ Watchdog Input — ✔ Manual-Reset Input ✔ — Active-High Reset SUFFIX MAX823 ✔ Typical Operating Circuit appears at end of data sheet. Marking Information appears at end of data sheet. __________________________________________________________Pin Configurations TOP VIEW RESET 1 GND 2 5 VCC MAX823 MR 3 GND 2 4 SOT23-5 RESET 1 WDI 5 VCC MAX824 RESET 3 GND 2 4 WDI SOT23-5 RESET 1 5 VCC MAX825 RESET 3 4 MR SOT23-5 *Patents Pending ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX823/MAX824/MAX825 _______________General Description The MAX823/MAX824/MAX825* microprocessor (µP) 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. MAX823/MAX824/MAX825 5-Pin Microprocessor Supervisory Circuits 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/µs Continuous Power Dissipation (TA = +70°C) SOT23-5 (derate 7.1mW/°C above +70°C)...................571mW Operating Temperature Range MAX82_EUK .....................................................-40°C to +85°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+300°C 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 = +25°C.) (Note 1) PARAMETER Operating Voltage Range Supply Current SYMBOL VCC ISUPPLY CONDITIONS TA = 0°C to +70°C 1.0 TA = -40°C to +85°C 1.2 WDI and MR unconnected MR unconnected MAX82_L MAX82_M Reset Threshold VRST MAX82_T MAX82_S MAX82_R Reset Threshold Hysteresis MIN 2 MAX 5.5 MAX823L/M, MAX824L/M 10 24 MAX823T/S/R, MAX824T/S/R 5 12 4.5 12 3 8 4.63 4.70 MAX825L/M MAX825T/S/R TA = +25°C 4.56 TA = -40°C to +85°C 4.50 TA = +25°C 4.31 TA = -40°C to +85°C 4.25 TA = +25°C 3.04 TA = -40°C to +85°C 3.00 TA = +25°C 2.89 TA = -40°C to +85°C 2.85 TA = +25°C 2.59 TA = -40°C to +85°C 2.55 V µA 4.45 4.50 3.08 3.11 3.15 2.93 V 2.96 3.00 2.63 2.66 2.70 10 MAX82_T/S/R 5 mV 40 tRP UNITS 4.75 4.38 MAX82_L/M Reset Threshold Temperature Coefficient Reset Timeout Period TYP ppm/°C MAX82_L/M 140 200 280 MAX82_T/S/R 140 200 280 _______________________________________________________________________________________ ms 5-Pin Microprocessor Supervisory Circuits (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 = +25°C.) (Note 1) PARAMETER SYMBOL VOH RESET Output Voltage VOL RESET Output Short-Circuit Current (Note 2) ISOURCE VOH RESET Output Voltage VOL VCC to RESET Delay CONDITIONS MIN MAX82_L/M, VCC = VRST max, ISOURCE = 120µA VCC - 1.5 MAX82_T/S/R, VCC = VRST max, ISOURCE = 30µA 0.8VCC TYP MAX MAX82_L/M, VCC = VRST min, ISINK = 3.2mA 0.4 MAX82_T/S/R, VCC = VRST min, ISINK = 1.2mA 0.3 TA = 0°C to +70°C, VCC = 1V, VCC falling, ISINK = 50µA 0.3 TA = -40°C to +85°C, VCC = 1.2V, VCC falling, VBATT = 0V, ISINK = 100µA 0.3 MAX82_L/M, RESET = 0V, VCC = 5.5V 800 MAX82_T/S/R, RESET = 0V, VCC = 3.6V 400 VCC > 1.8V, ISOURCE = 150µA UNITS V µA 0.8VCC MAX824L/M, MAX825L/M, VCC = VRST max, ISINK = 3.2mA 0.4 MAX824T/S/R, MAX825T/S/R, VCC = VRST max, ISINK = 1.2mA 0.3 VRST - VCC = 100mV 20 V µs WATCHDOG INPUT (MAX823/MAX824) Watchdog Timeout Period tWD WDI Pulse Width tWDI WDI Input Threshold (Note 3) VIL VIH 1.12 VIL = 0.4V, VIH = 0.8VCC VCC = 5V WDI = 0V, time average 2.40 0.7VCC 120 -20 sec ns 0.3VCC WDI = VCC, time average WDI Input Current (Note 4) 1.60 50 160 -15 V µA MANUAL-RESET INPUT (MAX823/MAX825) MR Input Threshold MR Pulse Width VIL 0.3VCC VIH 0.7VCC 1.0 MR Noise Immunity (pulse width with no reset) ns 500 MR Pull-Up Resistance (internal) Note 1: Note 2: Note 3: Note 4: µs 100 MR to Reset Delay 35 V 52 ns 75 kΩ 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 µP 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 10µA maximum leakage current and a maximum capacitive load of 200pF. This output device must be able to source and sink at least 200µA when active. _______________________________________________________________________________________ 3 MAX823/MAX824/MAX825 ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (MAX823L, VCC = +5V, TA = +25°C, unless otherwise noted.) RESET TIMEOUT PERIOD vs. TEMPERATURE 10.5 10.0 9.5 9.0 8.5 230 VCC FALLING 220 210 200 190 180 170 25 20 15 10 5 160 8.0 150 7.5 -20 0 20 40 60 80 0 -40 100 -20 0 20 40 60 80 100 -20 0 20 40 60 80 100 TEMPERATURE (°C) TEMPERATURE (°C) WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE NORMALIZED RESET THRESHOLD VOLTAGE vs. TEMPERATURE MAXIMUM VCC TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.06 1.04 1.02 1.00 0.98 -20 0 20 40 60 TEMPERATURE (°C) 80 100 140 120 100 80 RESET OCCURS ABOVE CURVE 60 40 0.96 20 0.94 1.0 160 MAX823/4/5-06 1.9 TRANSIENT DURATION (µs) MAX823/4/5-04 2.0 -40 -40 TEMPERATURE (°C) NORMALIZED RESET THRESHOLD (V) -40 4 30 MAX823/4/5-02 240 PROPAGATION DELAY (µs) 11.5 11.0 250 MAX823/4/5-05 SUPPLY CURRENT (µA) 12.0 RESET TIMEOUT PERIOD (ms) MAX823/4/5-01 12.5 RESET COMPARATOR PROPAGATION DELAY vs. TEMPERATURE MAX823/4/5-03 VCC SUPPLY CURRENT vs. TEMPERATURE WATCHDOG TIMEOUT PERIOD (sec) MAX823/MAX824/MAX825 5-Pin Microprocessor Supervisory Circuits 0 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 0 20 40 60 80 100 120 140 160 180 200 RESET THRESHOLD OVERDRIVE (mV), VRST - VCC _______________________________________________________________________________________ 5-Pin Microprocessor Supervisory Circuits 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. 1 1 1 RESET 2 2 2 GND 3 — 4 MR — 3 3 RESET 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 52kΩ 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. 4 4 — WDI 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. 5 5 5 VCC Supply Voltage VCC MAX823 MAX824 MAX825 RESET GENERATOR VCC RESET RESET (MAX824/MAX825 ONLY) 1.25V MR (MAX823/MAX825 ONLY) WDI (MAX823/MAX824 ONLY) WATCHDOG TRANSITION DETECTOR WATCHDOG TIMER GND Figure 1. Functional Diagram _______________________________________________________________________________________ 5 MAX823/MAX824/MAX825 ______________________________________________________________Pin Description MAX823/MAX824/MAX825 5-Pin Microprocessor Supervisory Circuits _______________Detailed Description RESET Output A microprocessor’s (µP’s) reset input starts the µP in a known state. The MAX823/MAX824/MAX825 µP 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 µP’s activity. If the µP 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 10µA and the maximum allowable load capacitance is 200pF. Manual-Reset Input (MAX823/MAX825) __________Applications Information Many µP-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 52kΩ 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 0.1µF capacitor from MR to GND to provide additional noise immunity. 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 160µA can flow into WDI. VCC VCC 1V Watchdog Input Current VRST VRST tRST 1V RESET* RESET tRP tRD RESET tRP tRD tRP tWD tRP WDI GND *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 The RESET output maximum pull-up current is 800µA for L/M versions (400µA for T/S/R versions). This allows µPs with bidirectional resets, such as the 68HC11, to force RESET low when the MAX823/MAX824/MAX825 are pulling RESET high (Figure 4). 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 µP 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 15µs or less will not trigger a reset pulse. An optional 0.1µF bypass capacitor mounted close to VCC provides additional transient immunity. 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. START SET WDI HIGH VCC VCC MAX823 MAX824 MAX825 RESET GENERATOR VCC ISOURCE MAX = 800µA L, M 400µA T, S, R RESET µP PROGRAM CODE SUBROUTINE OR PROGRAM LOOP SET WDI LOW GND GND RETURN Figure 4. Interfacing to µPs with Bidirectional Resets Figure 5. Watchdog Flow Diagram _______________________________________________________________________________________ 7 MAX823/MAX824/MAX825 Interfacing to µPs with Bidirectional Reset Pins __________Typical Operating Circuit ___________________Chip Information TRANSISTOR COUNT: 607 VCC VCC VCC RESET RESET MAX823 µP WDI MANUAL RESET ______________Package Information I/O MR GND 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 SOT5L.EPS MAX823/MAX824/MAX825 5-Pin Microprocessor Supervisory Circuits 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 © 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.