19-1868; Rev 2; 12/05 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer The MAX6821–MAX6825 are low-voltage microprocessor (µP) supervisory circuits that combine voltage monitoring, watchdog timer, and manual reset input functions in a 5-pin SOT23 package. Microprocessor supervisory circuits significantly improve system reliability and accuracy compared to separate ICs or discrete components. These devices assert a reset signal whenever the monitored voltage drops below its preset threshold, keeping it asserted for a minimum timeout period after VCC rises above the threshold. In addition, a watchdog timer monitors against code execution errors. A debounced manual reset is also available. The MAX6821–MAX6825 monitor voltages from +1.8V to +5.0V. These outputs are guaranteed to be in the correct state for VCC down to +1.0V. Nine preprogrammed reset threshold voltages are available (see the Threshold Suffix Guide). The MAX6821, MAX6822, and MAX6823 all have a manual reset input and a watchdog timer. The MAX6821 has push-pull RESET, the MAX6822 has open-drain RESET, and the MAX6823 has push-pull RESET. The MAX6824 has a watchdog timer and both push-pull RESET and push-pull RESET. The MAX6825 has a manual reset input and both push-pull RESET and push-pull RESET. The Selector Guide explains the functions offered in this series of parts. ________________________Applications Set-Top Boxes Computers and Controllers Embedded Controllers Intelligent Instruments Automotive Systems Critical µP Monitoring Portable/BatteryPowered Equipment TOP VIEW RESET(RESET) 1 5 VCC MAX6821 MAX6822 MAX6823 MR 3 (RESET) MAX6821 ONLY ♦ Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V Supplies ♦ 140ms (min) Reset Timeout Delay ♦ 1.6s Watchdog Timeout Period (MAX6821/MAX6822/MAX6823/MAX6824) ♦ Manual Reset Input (MAX6821/MAX6822/MAX6823/MAX6825) ♦ Three Reset Output Options Push-Pull RESET Push-Pull RESET Open-Drain RESET ♦ Guaranteed Reset Valid to VCC = +1.0V ♦ Immune to Short Negative VCC Transients ♦ No External Components ♦ Small 5-Pin SOT23 Packages Ordering Information TEMP RANGE PIN-PACKAGE MAX6821_UK-T PART* -40°C to +125°C 5 SOT23-5 MAX6822_UK-T -40°C to +125°C 5 SOT23-5 MAX6823_UK-T -40°C to +125°C 5 SOT23-5 MAX6824_UK-T -40°C to +125°C 5 SOT23-5 MAX6825_UK-T -40°C to +125°C 5 SOT23-5 *Insert the desired suffix letter (from the table below) into the blank to complete the part number Devices are available in both leaded and lead-free packaging. Specify lead-free by replacing “-T” with “+T” when ordering. Threshold Suffix Guide Pin Configurations GND 2 Features 4 WDI SOT23-5 Pin Configurations continued at end of data sheet. Typical Operating Circuit appears at end of data sheet. SUFFIX RESET THRESHOLD (V) L 4.63 M 4.38 T 3.08 S 2.93 R 2.63 Z 2.32 Y 2.19 W 1.67 V 1.58 Note: Bold indicates standard versions. Samples are typically available for standard versions only. All parts require a 2.5k minimum order increment. Contact factory for availability. Selector Guide appears at end of data sheet. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX6821–MAX6825 General Description MAX6821–MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer ABSOLUTE MAXIMUM RATINGS VCC to GND ...........................................................-0.3V to +6.0V Open-Drain RESET................................................-0.3V to +6.0V Push-Pull RESET, RESET, MR, WDI ...........-0.3V to (VCC + 0.3V) Input Current (VCC) .............................................................20mA Output Current (RESET, RESET).........................................20mA Continuous Power Dissipation (TA = +70°C) 5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+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 = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC = +1.53V to +2.0V for MAX682_W/V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1) PARAMETER Operating Voltage Range SYMBOL VCC CONDITIONS ICC TA = -40°C to +125°C 1.2 5.5 VCC = +3.6V, no load MAX682_L MAX682_M MAX682_T MAX682_S VTH MAX682_R MAX682_Z MAX682_Y MAX682_W MAX682_V TA = -40°C to +85°C 2 7 TA = -40°C to +125°C V 20 16 25 TA = -40°C to +85°C 5 12 TA = -40°C to +125°C µA 20 TA = -40°C to +85°C 4.50 4.63 4.75 TA = -40°C to +125°C 4.47 4.63 4.78 TA = -40°C to +85°C 4.25 4.38 4.50 TA = -40°C to +125°C 4.22 4.38 4.53 TA = -40°C to +85°C 3.00 3.08 3.15 TA = -40°C to +125°C 2.97 3.08 3.17 TA = -40°C to +85°C 2.85 2.93 3.00 TA = -40°C to +125°C 2.83 2.93 3.02 TA = -40°C to +85°C 2.55 2.63 2.70 TA = -40°C to +125°C 2.53 2.63 2.72 TA = -40°C to +85°C 2.25 2.32 2.38 TA = -40°C to +125°C 2.24 2.32 2.40 TA = -40°C to +85°C 2.12 2.19 2.25 TA = -40°C to +125°C 2.11 2.19 2.27 TA = -40°C to +85°C 1.62 1.67 1.71 TA = -40°C to +125°C 1.61 1.67 1.72 TA = -40°C to +85°C 1.52 1.58 1.62 VCC = VTH to (VTH - 100mV) UNITS 30 TA = -40°C to +85°C Reset Threshold Hysteresis tRD 10 TA = -40°C to +125°C Reset Threshold Temperature Coefficient VCC to Reset Output Delay MAX 5.5 VCC = +3.6V, no load (MAX6825 only) VCC Reset Threshold (VCC Falling) TYP 1.0 VCC = +5.5V, no load VCC Supply Current (MR and WDI Unconnected) MIN TA = 0°C to +85°C V 60 ppm/°C 2 ✕ VTH mV 20 µs _______________________________________________________________________________________ Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer (VCC = +4.5V to +5.5V for MAX682_L/M, VCC = +2.7V to +3.6V for MAX682_T/S/R, VCC = +2.1V to +2.75V for MAX682_Z/Y, VCC = +1.53V to +2.0V for MAX682_W/V, TA = -40°C to +125°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1) PARAMETER Reset Timeout Period RESET Output LOW (Push-Pull or Open-Drain) RESET Output HIGH (Push-Pull Only) Open-Drain RESET Output Leakage Current (Note 1) SYMBOL tRP CONDITIONS MIN TYP TA = -40°C to +85°C 140 200 TA = -40°C to +125°C 100 RESET Output LOW (Push-Pull Only) 280 320 VCC ≥ 1.0V, ISINK = 50µA, reset asserted, TA = 0°C to +85°C VOL VOH ILKG VOH VOL UNITS ms 0.3 VCC ≥ 1.2V, ISINK = 100µA, reset asserted 0.3 VCC ≥ 2.55V, ISINK = 1.2mA, reset asserted 0.3 VCC ≥ 4.25V, ISINK = 3.2mA, reset asserted 0.4 VCC ≥ 1.8V, ISOURCE = 200µA, reset not asserted 0.8 ✕ VCC VCC ≥ 3.15V, ISOURCE = 500µA, reset not asserted 0.8 ✕ VCC VCC ≥ 4.75V, ISOURCE = 800µA, reset not asserted 0.8 ✕ VCC V V VCC > VTH, RESET not asserted VCC ≥ 1.0V, ISOURCE = 1µA, reset asserted, TA = 0°C to +85°C RESET Output HIGH (Push-Pull Only) MAX 1.0 µA 0.8 ✕ VCC VCC ≥ 1.50V, ISOURCE = 100µA, reset asserted 0.8 ✕ VCC VCC ≥ 2.55V, ISOURCE = 500µA, reset asserted 0.8 ✕ VCC VCC ≥ 4.25V, ISOURCE = 800µA, reset asserted 0.8 ✕ VCC V VCC ≥ 1.8V, ISINK = 500µA, reset not asserted 0.3 VCC ≥ 3.15V, ISINK = 1.2mA, reset not asserted 0.3 VCC ≥ 4.75V, ISINK = 3.2mA, reset not asserted 0.4 V MANUAL RESET INPUT (MAX6821/MAX6822/MAX6823/MAX6825) VIL MR Input Voltage 0.3 ✕ VCC VIH 0.7 ✕ VCC MR Minimum Input Pulse 1 V µs MR Glitch Rejection 100 ns MR to Reset Delay 200 ns MR Pullup Resistance 25 50 75 TA = -40°C to +85°C 1.12 1.60 2.40 TA = -40°C to +125°C 0.80 kΩ WATCHDOG INPUT (MAX6821/MAX6822/MAX6823/MAX6824) Watchdog Timeout Period tWD WDI Pulse Width (Note 2) tWDI WDI Input Voltage WDI Input Current 2.60 50 ns VIL 0.3 ✕ VCC 0.7 ✕ VCC VIH IWDI WDI = VCC, time average WDI = 0, time average 120 -20 s -15 160 V µA Note 1: Over-temperature limits are guaranteed by design and not production tested. Devices tested at TA = +25°C. Note 2: Guaranteed by design and not production tested. _______________________________________________________________________________________ 3 MAX6821–MAX6825 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) RESET TIMEOUT PERIOD vs. TEMPERATURE 9 6 VCC = +1.8V, V VERSION 5 4 220 210 200 190 180 0 20 40 60 80 15 10 5 0 150 -40 -20 20 170 160 3 25 100 120 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) WATCHDOG TIMEOUT PERIOD vs. TEMPERATURE NORMALIZED RESET THRESHOLD DELAY vs. TEMPERATURE MAXIMUM VCC TRANSIENT DURATION vs. RESET THRESHOLD OVERDRIVE 1.06 MAX6821 toc04 2.0 1.9 1.04 RESET THRESHOLD (V) 1.8 1.7 1.6 1.5 1.4 1.3 1.2 1.02 1.00 0.98 120 MAX6821 toc06 7 VCC = +3.3V, S VERSION 230 VCC FALLING, VCC = VTH - 100mV 30 TRANSIENT DURATION (µs) 8 35 PROPAGATION DELAY (µs) 10 240 MAX6821 toc05 SUPPLY CURRENT (µA) 11 VCC = +5V, L VERSION 250 MAX6821 toc02 12 RESET TIMEOUT PERIOD (ms) MAX6821 toc01 13 VCC TO RESET OUTPUT DELAY vs. TEMPERATURE MAX6821 toc03 SUPPLY CURRENT vs. TEMPERATURE WATCHDOG TIMEOUT PERIOD (s) 100 80 RESET OCCURS ABOVE CURVE 60 40 20 0.96 1.1 0.94 -40 -20 -40 -20 0 20 40 60 80 100 120 0 0 TEMPERATURE (°C) 20 40 60 100 120 0 TEMPERATURE (°C) 20 40 60 80 100 120 140 160 180 200 RESET THRESHOLD OVERDRIVE (mV), VTH - VCC VOLTAGE OUTPUT HIGH vs. SOURCE CURRENT VOLTAGE OUTPUT LOW vs. SINK CURRENT 2.92 MAX6821 toc07 0.35 80 VCC = +2.9V 0.30 VCC = +2.9V 2.90 2.88 0.25 MAX6821 toc08 1.0 2.86 VOUT (V) VOUT (V) MAX6821–MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer 0.20 0.15 2.84 2.82 2.80 0.10 2.78 0.05 2.76 2.74 0 0 1 2 3 4 ISINK (mA) 4 5 6 7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 ISOURCE (mA) _______________________________________________________________________________________ Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer PIN NUMBERS PIN NAME MAX6821 MAX6822 MAX6823 MAX6824 MAX6825 1 1 1 2 3 2 3 2 1 1 RESET Active-Low Open-Drain or Push-Pull Reset Output. RESET changes from high to low when the VCC input drops below the selected reset threshold, MR is pulled low, or the watchdog triggers a reset. RESET remains low for the reset timeout period after VCC exceeds the device reset threshold, MR goes low to high, or the watchdog triggers a reset. Active-High Push-Pull Reset Output. RESET changes from low to high when the VCC input drops below the selected reset threshold, MR is pulled low, or the watchdog triggers a reset. RESET remains high for the reset timeout period after VCC exceeds the device reset threshold, MR goes low to high, or the watchdog triggers a reset. 3 3 RESET 2 2 GND 3 4 4 4 4 4 5 5 5 5 5 FUNCTION Ground MR Active-Low Manual Reset Input. Internal 50kΩ pullup to VCC. Pull low to force a reset. Reset remains active as long as MR is low and for the reset timeout period after MR goes high. Leave unconnected or connect to VCC if unused. WDI Watchdog Input. If WDI remains high or low for longer than the watchdog timeout period, the internal watchdog timer runs out and a reset is triggered for the reset timeout period. The internal watchdog timer clears whenever reset is asserted, the manual reset is asserted, or 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. VCC Supply Voltage and Input for Reset Threshold Monitor Detailed Description RESET/RESET Output A µP’s reset input starts the µP in a known state. The MAX6821–MAX6825 µP supervisory circuits assert a reset to prevent code-execution errors during powerup, power-down, and brownout conditions. Whenever VCC falls below the reset threshold, the reset output asserts low for RESET and high for RESET. Once VCC exceeds the reset threshold, an internal timer keeps the reset output asserted for the specified reset timeout period (tRP); after this interval, reset output returns to its original state (see Figure 2). Manual Reset Input Many µP-based products require manual reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. On the MAX6821/ MAX6822/MAX6823/MAX6825, a logic low on MR asserts a reset. Reset remains asserted while MR is low, and for the timeout period (140ms min) after it returns high. MR has an internal 50kΩ pullup 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. Watchdog Input In the MAX6821–MAX6824, the watchdog circuit monitors the µP’s activity. If the µP does not toggle (low to high or high to low) the watchdog input (WDI) within the watchdog timeout period (1.6s nominal), reset asserts for the reset timoeout period. The internal 1.6s timer can be cleared by either a reset pulse or by toggling WDI. The WDI can detect 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 (see Figure 3). _______________________________________________________________________________________ 5 MAX6821–MAX6825 Pin Description MAX6821–MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer VCC MAX6821– MAX6825 RESET (MAX6822–MAX6825) RESET GENERATOR RESET (MAX6821/MAX6824/ MAX6825) VCC 1.26V MR (MAX6821–MAX6823, MAX6825) WATCHDOG TRANSITION DETECTOR WDI (MAX6821–MAX6824) WATCHDOG TIMER GND Figure 1. Functional Diagram 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 1.6s timer every 1.4s. When WDI is three-stated or unconnected, the maximum allowable leakage current is 10µA and the maximum allowable load capacitance is 200pF. Applications Information VCC 1V VTH VTH 1V RESET tRP tRD RESET tRP tRD GND Figure 2. Reset Timing Diagram Watchdog Input Current The MAX6821/MAX6822/MAX6823/MAX6824 WDI inputs are internally driven through a buffer and series resistor from the watchdog timer (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. 6 Interfacing to µPs with Bidirectional Reset Pins Since the RESET output on the MAX6822 is open drain, it interfaces easily with µPs that have bidirectional reset pins, such as the Motorola 68HC11. Connecting the µP supervisor’s RESET output directly to the microcontroller’s RESET pin with a single pullup resistor allows either device to assert reset (see Figure 4). Negative-Going VCC Transients These supervisors are relatively immune to short-duration, negative-going VCC transients (glitches), which usually do not require the entire system to shut down. _______________________________________________________________________________________ Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer MAX6821–MAX6825 VCC tRST VCC RESET* VCC MAX6822 tRP tWD RESET tRP RESET µP RESET GENERATOR WDI GND GND *RESET IS THE INVERSE OF RESET. Figure 3. Watchdog Timing Relationship Figure 4. Interfacing Open-Drain RESET to µPs with Bidirectional Reset I/O Resets are issued to the µP during power-up, powerdown, and brownout conditions. The Typical Operating Characteristics show a graph of the MAX6821– MAX6825’s Maximum VCC Transient Duration vs. Reset Threshold Overdrive, for which reset pulses are not generated. The graph was produced using negativegoing VCC pulses, starting at the standard monitored voltage and ending below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the maximum pulse width that a negativegoing 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 20µs or less will not trigger a reset pulse. START SET WDI HIGH PROGRAM CODE SUBROUTINE OR PROGRAM LOOP SET WDI LOW RETURN Watchdog Software Considerations 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. Figure 5. Watchdog Flow Diagram Typical Operating Circuit VCC VCC VCC RESET RESET µP MAX6823 WDI MANUAL RESET MR I/O GND _______________________________________________________________________________________ 7 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer MAX6821–MAX6825 Selector Guide FUNCTION ACTIVE-LOW RESET ACTIVE-HIGH RESET OPEN-DRAIN RESET WATCHDOG INPUT MANUAL RESET INPUT MAX6821 MAX6822 — ✔ — ✔ ✔ — — ✔ ✔ ✔ MAX6823 ✔ — — ✔ ✔ MAX6824 ✔ ✔ — ✔ — MAX6825 ✔ ✔ — — ✔ Pin Configurations (continued) TOP VIEW RESET 1 GND 2 5 VCC MAX6824 RESET 3 RESET 1 GND 2 4 WDI SOT23-5 5 VCC 4 MR MAX6825 RESET 3 SOT23-5 Chip Information TRANSISTOR COUNT: 750 PROCESS: BiCMOS 8 _______________________________________________________________________________________ Ultra-Low-Voltage SOT23 µP Supervisor with Manual Reset and Watchdog Timer SOT-23 5L .EPS PACKAGE OUTLINE, SOT-23, 5L 21-0057 E 1 1 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. 9 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc. MAX6821–MAX6825 Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)