MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer General Description Features The MAX6821–MAX6825 are low-voltage microproces- ● Monitors +1.8V, +2.5V, +3.0V, +3.3V, +5.0V Supplies sor (µP) supervisory circuits that combine voltage mon- ● 140ms (min) Reset Timeout Delay itoring, watchdog timer, and manual reset input func- ● 1.6s Watchdog Timeout Period (MAX6821/MAX6822/ tions in a 5-pin SOT23 package. Microprocessor super- MAX6823/MAX6824) visory circuits significantly improve system reliability and ● Manual Reset Input (MAX6821/MAX6822/MAX6823/ accuracy compared to separate ICs or discrete compo- MAX6825) nents. These devices assert a reset signal whenever the monitored voltage drops below its preset threshold, keep- ● Three Reset Output Options ing it asserted for a minimum timeout period after VCC rises Push-Pull RESET above the threshold. In addition, a watchdog timer monitors Push-Pull RESET against code execution errors. A debounced manual reset Open-Drain RESET is also available. The MAX6821–MAX6825 monitor voltag- ● Guaranteed Reset Valid to VCC = +1.0V es from +1.8V to +5.0V. These outputs are guaranteed to be in the correct state for VCC down to +1.0V. ● Immune to Short Negative VCC Transients ● No External Components Nine preprogrammed reset threshold voltages are available (see the Threshold Suffix Guide). The ● Small 5-Pin SOT23 Packages MAX6821, MAX6822, and MAX6823 all have a manual Ordering Information reset input and a watchdog timer. The MAX6821 has push-pull RESET, the MAX6822 has open-drain RESET, PART* TEMP RANGE PIN-PACKAGE and the MAX6823 has push-pull RESET. The MAX6824 MAX6821_UK-T -40°C to +125°C 5 SOT23-5 has a watchdog timer and both push-pull RESET and MAX6822_UK-T -40°C to +125°C 5 SOT23-5 push-pull RESET. The MAX6825 has a manual reset MAX6823_UK-T -40°C to +125°C 5 SOT23-5 input and both push-pull RESET and push-pull RESET. MAX6824_UK-T -40°C to +125°C 5 SOT23-5 The Selector Guide explains the functions offered in MAX6825_UK-T -40°C to +125°C 5 SOT23-5 this series of parts. *Insert the desired suffix letter (from the table below) into the blank to complete the part number Applications Devices are available in both leaded and lead(Pb)-free packag- ● Set-Top Boxes ● Intelligent Instruments ing.Specify lead-free by replacing “-T” with “+T” when ordering. ● Computers and Con- ● Critical µP Monitoring Threshold Suffix Guide trollers ● Portable/Battery- ● Embedded Controllers Powered Equipment SUFFIX RESET THRESHOLD (V) L 4.63 Pin Configurations M 4.38 T 3.08 TOP VIEW S 2.93 R 2.63 RESET(RESET) 1 5 VCC Z 2.32 MAX6821 GND 2 MAX6822 Y 2.19 MAX6823 W 1.67 MR 3 4 WDI V 1.58 SOT23-5 Note: Bold indicates standard versions. Samples are typically (RESET) MAX6821 ONLY available for standard versions only. All parts require a 2.5k Pin Configurations continued at end of data sheet. minimum order increment. Contact factory for availability. Typical Operating Circuit appears at end of data sheet. Selector Guide appears at end of data sheet. 19-1868; Rev 3; 7/14

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Absolute Maximum Ratings VCC to GND .........................................................-0.3V to +6.0V Operating Temperature Range .........................-40°C to +125°C Open-Drain RESET ..............................................-0.3V to +6.0V Junction Temperature ......................................................+150°C Push-Pull RESET, RESET, MR, WDI .......-0.3V to (VCC + 0.3V) Storage Temperature Range ............................-65°C to +150°C Input Current (VCC) ............................................................20mA Lead Temperature (soldering, 10s) .................................+300°C Output Current (RESET, RESET) ......................................20mA Continuous Power Dissipation (TA = +70°C) 5-Pin SOT23 (derate 7.1mW/°C above +70°C) ..........571mW 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 SYMBOL CONDITIONS MIN TYP MAX UNITS TA = 0°C to +85°C 1.0 5.5 Operating Voltage Range VCC V TA = -40°C to +125°C 1.2 5.5 TA = -40°C to +85°C 10 20 VCC = +5.5V, no load TA = -40°C to +125°C 30 (VMCRC aSnudp pWlyD CI uUrnrecnotnnected) ICC VCC = +3.6V, no load TTAA == --4400°°CC ttoo ++8152°5C°C 7 1265 µA VCC = +3.6V, no load TA = -40°C to +85°C 5 12 (MAX6825 only) TA = -40°C to +125°C 20 TA = -40°C to +85°C 4.50 4.63 4.75 MAX682_L TA = -40°C to +125°C 4.47 4.63 4.78 TA = -40°C to +85°C 4.25 4.38 4.50 MAX682_M TA = -40°C to +125°C 4.22 4.38 4.53 TA = -40°C to +85°C 3.00 3.08 3.15 MAX682_T TA = -40°C to +125°C 2.97 3.08 3.17 TA = -40°C to +85°C 2.85 2.93 3.00 MAX682_S TA = -40°C to +125°C 2.83 2.93 3.02 V(VCCCC R Feaslleint gT)hreshold VTH MAX682_R TA = -40°C to +85°C 2.55 2.63 2.70 V TA = -40°C to +125°C 2.53 2.63 2.72 TA = -40°C to +85°C 2.25 2.32 2.38 MAX682_Z TA = -40°C to +125°C 2.24 2.32 2.40 TA = -40°C to +85°C 2.12 2.19 2.25 MAX682_Y TA = -40°C to +125°C 2.11 2.19 2.27 TA = -40°C to +85°C 1.62 1.67 1.71 MAX682_W TA = -40°C to +125°C 1.61 1.67 1.72 MAX682_V TA = -40°C to +85°C 1.52 1.58 1.62 Reset Threshold Temperature 60 ppm/°C Coefficient Reset Threshold Hysteresis 2 × VTH mV VCC to Reset Output Delay tRD VCC = VTH to (VTH - 100mV) 20 µs www.maximintegrated.com Maxim Integrated │ 2

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Electrical Characteristics (continued) (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 SYMBOL CONDITIONS MIN TYP MAX UNITS TA = -40°C to +85°C 140 200 280 Reset Timeout Period tRP ms TA = -40°C to +125°C 100 320 VCC ≥ 1.0V, ISINK = 50µA, reset asserted, 0.3 TA = 0°C to +85°C RESET Output LOW VOL VCC ≥ 1.2V, ISINK = 100µA, reset asserted 0.3 V (Push-Pull or Open-Drain) VCC ≥ 2.55V, ISINK = 1.2mA, reset asserted 0.3 VCC ≥ 4.25V, ISINK = 3.2mA, reset asserted 0.4 VasCsCe r≥te 1d.8V, ISOURCE = 200µA, reset not 0.8 × VCC R(PEuSsEh-TP Oulul Otpnulty H)IGH VOH VasCsCe r≥te 3d.15V, ISOURCE = 500µA, reset not 0.8 × VCC V VasCsCe r≥te 4d.75V, ISOURCE = 800µA, reset not 0.8 × VCC Open-Drain RESET Output Leakage Current (Note 1) ILKG VCC > VTH, RESET not asserted 1.0 µA VTAC C= ≥0 °1C.0 tVo ,+ IS85O°UCRCE = 1µA, reset asserted, 0.8 × VCC RESET Output HIGH (Push-Pull Only) VOH VCC ≥ 1.50V, ISOURCE = 100µA, reset asserted 0.8 × VCC V VCC ≥ 2.55V, ISOURCE = 500µA, reset asserted 0.8 × VCC VCC ≥ 4.25V, ISOURCE = 800µA, reset asserted 0.8 × VCC VCC ≥ 1.8V, ISINK = 500µA, reset not asserted 0.3 RESET Output LOW (Push-Pull Only) VOL VCC ≥ 3.15V, ISINK = 1.2mA, reset not asserted 0.3 V VCC ≥ 4.75V, ISINK = 3.2mA, reset not asserted 0.4 MANUAL RESET INPUT (MAX6821/MAX6822/MAX6823/MAX6825) VIL 0.3 × VCC MR Input Voltage V VIH 0.7 × VCC MR Minimum Input Pulse 1 µs MR Glitch Rejection 100 ns MR to Reset Delay 200 ns MR Pullup Resistance 25 50 75 kΩ WATCHDOG INPUT (MAX6821/MAX6822/MAX6823/MAX6824) TA = -40°C to +85°C 1.12 1.60 2.40 Watchdog Timeout Period tWD s TA = -40°C to +125°C 0.80 2.60 WDI Pulse Width (Note 2) tWDI 50 ns VIL 0.3 × VCC WDI Input Voltage V VIH 0.7 × VCC WDI = VCC, time average 120 160 WDI Input Current IWDI µA WDI = 0, time average -20 -15 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. www.maximintegrated.com Maxim Integrated │ 3

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) SUPPLY CURRENT RESET TIMEOUT PERIOD VCC TO RESET OUTPUT DELAY vs. TEMPERATURE vs. TEMPERATURE vs. TEMPERATURE µSUPPLY CURRENT (A) 1111576980213 VCVVCCC CC= ==+ 5++V31,.. 38LVV V,, ESVR VVSEEIORRSNSIIOONN MAX6821 toc01 RESET TIMEOUT PERIOD (ms)111222222798102435000000000 MAX6821 toc02 µPROPAGATION DELAY (s) 121323005055 VCC FALLING, VCC = VTH - 100mV MAX6821 toc03 5 4 160 3 150 0 -40 -20 0 20 40 60 80 100 120 -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 NORMALIZED RESET THRESHOLD MAXIMUM VCC TRANSIENT DURATION vs. TEMPERATURE DELAY vs. TEMPERATURE vs. RESET THRESHOLD OVERDRIVE G TIMEOUT PERIOD (s) 1111112.......4657980 MAX6821 toc04 T THRESHOLD (V)1111....00000426 MAX6821 toc05 µENT DURATION (s)1168020000 RABEOSEVTE OCCUCRUVRES MAX6821 toc06 ATCHDO 11..23 RESE0.98 TRANSI 40 W 0.96 20 1.1 1.0 0.94 0 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 80 100 120 0 20 40 60 80 100120140160180200 TEMPERATURE (°C) TEMPERATURE (°C) RESET THRESHOLD OVERDRIVE (mV), VTH - VCC VOLTAGE OUTPUT LOW VOLTAGE OUTPUT HIGH vs. SINK CURRENT vs. SOURCE CURRENT 00..3305 VCC = +2.9V MAX6821 toc07 222...989082 VCC = +2.9V MAX6821 toc08 0.25 2.86 V (V)OUT00..2105 V (V)OUT22..8824 2.80 0.10 2.78 0.05 2.76 0 2.74 0 1 2 3 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 ISINK (mA) ISOURCE (mA) www.maximintegrated.com Maxim Integrated │ 4

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Pin Description PIN NUMBERS PIN FUNCTION MAX6821 MAX6822 MAX6823 MAX6824 MAX6825 NAME 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 1 1 1 1 RESET 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 1 3 3 RESET high for the reset timeout period after VCC exceeds the device reset threshold, MR goes low to high, or the watchdog triggers a reset. 2 2 2 2 2 GND Ground Active-Low Manual Reset Input. Internal 50kΩ pullup to VCC. Pull low to force a reset. Reset remains active as long as MR is 3 3 3 4 MR low and for the reset timeout period after MR goes high. Leave unconnected or connect to VCC if unused. 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 4 4 4 4 WDI 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. 5 5 5 5 5 VCC Supply Voltage and Input for Reset Threshold Monitor Detailed Description returns high. MR has an internal 50kΩ pullup resistor, so it can be left open if not used. This input can be dri- RESET/RESET Output ven with CMOS logic levels or with open-drain/collector A µP’s reset input starts the µP in a known state. The outputs. Connect a normally open momentary switch MAX6821–MAX6825 µP supervisory circuits assert a from MR to GND to create a manual reset function; reset to prevent code-execution errors during power-up, external debounce circuitry is not required. If MR is dri- power-down, and brownout conditions. Whenever VCC ven from long cables or the device is used in a noisy falls below the reset threshold, the reset output asserts environment, connect a 0.1µF capacitor from MR to low for RESET and high for RESET. Once VCC exceeds GND to provide additional noise immunity. the reset threshold, an internal timer keeps the reset out- Watchdog Input put asserted for the specified reset timeout period (tRP); after this interval, reset output returns to its original state In the MAX6821–MAX6824, the watchdog circuit moni- (see Figure 2). tors the µP’s activity. If the µP does not toggle (low to high or high to low) the watchdog input (WDI) within the Manual Reset Input watchdog timeout period (1.6s nominal), reset asserts Many µP-based products require manual reset capabili- for the reset timoeout period. The internal 1.6s timer ty, allowing the operator, a test technician, or external can be cleared by either a reset pulse or by toggling logic circuitry to initiate a reset. On the MAX6821/ WDI. The WDI can detect pulses as short as 50ns. MAX6822/MAX6823/MAX6825, a logic low on MR While reset is asserted, the timer remains cleared and asserts a reset. Reset remains asserted while MR is does not count. As soon as reset is released, the timer low, and for the timeout period (140ms min) after it starts counting (see Figure 3). www.maximintegrated.com Maxim Integrated │ 5

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) (MAX6821–MA X 6 8W2D4)I TWDRAEATTNCESCHITTDIOOORGN WATTICMHEDROG GND Figure 1. Functional Diagram Disable the watchdog function by leaving WDI uncon- nected or by three-stating the driver connected to WDI. VCC The watchdog input is internally driven low during the 1V VTH VTH 1V first 7/8 of the watchdog timeout period and high for the last 1/8 of the watchdog timeout period. When WDI is RESET tRP tRD 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 RESET tRP tRD GND maximum allowable load capacitance is 200pF. Applications Information Figure 2. Reset Timing Diagram Watchdog Input Current Interfacing to µPs with The MAX6821/MAX6822/MAX6823/MAX6824 WDI inputs Bidirectional Reset Pins are internally driven through a buffer and series resistor Since the RESET output on the MAX6822 is open drain, from the watchdog timer (Figure 1). When WDI is left it interfaces easily with µPs that have bidirectional reset unconnected, the watchdog timer is serviced within the pins, such as the Motorola 68HC11. Connecting the µP watchdog timeout period by a low-high-low pulse from supervisor’s RESET output directly to the microcon- the counter chain. For minimum watchdog input current troller’s RESET pin with a single pullup resistor allows (minimum overall power consumption), leave WDI low for either device to assert reset (see Figure 4). the majority of the watchdog timeout period, pulsing it low- high-low once within the first 7/8 of the watchdog timeout Negative-Going VCC Transients period to reset the watchdog timer. If WDI is externally These supervisors are relatively immune to short-dura- driven high for the majority of the timeout period, up to tion, negative-going VCC transients (glitches), which 160µA can flow into WDI. usually do not require the entire system to shut down. www.maximintegrated.com Maxim Integrated │ 6

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer VCC tRST VCC VCC RESET* MAX6822 tRP tWD tRP RESET RESET RESET µP 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, pow- er-down, and brownout conditions. The Typical Operating START 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 SET WDI HIGH graph was produced using negative-going VCC pulses, starting at the standard monitored voltage and ending PROGRAM CODE below the reset threshold by the magnitude indicated (reset threshold overdrive). The graph shows the max- imum pulse width that a negative-going VCC transient SUBROUTINE OR PROGRAM LOOP can typically have without triggering a reset pulse. As the SET WDI LOW 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 RETURN less will not trigger a reset pulse. Watchdog Software Considerations Figure 5. Watchdog Flow Diagram One way to help the watchdog timer monitor software Typical Operating Circuit 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-high-low. This VCC technique avoids a stuck loop, in which the watchdog VCC timer would continue to be reset inside the loop, keeping VCC the watchdog from timing out. RESET RESET Figure 5 shows an example of a flow diagram where the I/O driving the watchdog input is set high at the begin- MAX6823 µP ning of the program, set low at the beginning of every WDI I/O MR subroutine or loop, then set high again when the program MANUAL GND RESET 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. www.maximintegrated.com Maxim Integrated │ 7

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Selector Guide ACTIVE-LOW ACTIVE-HIGH OPEN-DRAIN WATCHDOG MANUAL FUNCTION RESET RESET RESET INPUT RESET INPUT MAX6821 — ✔ — ✔ ✔ MAX6822 — — ✔ ✔ ✔ MAX6823 ✔ — — ✔ ✔ MAX6824 ✔ ✔ — ✔ — MAX6825 ✔ ✔ — — ✔ Pin Configurations (continued) TOP VIEW RESET 1 5 VCC RESET 1 5 VCC MAX6824 MAX6825 GND 2 GND 2 RESET 3 4 WDI RESET 3 4 MR SOT23-5 SOT23-5 Chip Information Package Information TRANSISTOR COUNT: 750 For the latest package outline information and land patterns PROCESS: BiCMOS (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE PACKAGE LAND PATTERN OUTLINE NO. TYPE CODE NO. 5 SOT23 U5-1 21-0057 — www.maximintegrated.com Maxim Integrated │ 8

MAX6821/MAX6825 Low-Voltage SOT23 µP Supervisors with Manual Reset and Watchdog Timer Revision History REVISION REVISION PAGES DESCRIPTION NUMBER DATE CHANGED 3 7/14 No /V OPNs; removed automotive reference from Applications section 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2014 Maxim Integrated Products, Inc. │ 9

Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: M axim Integrated: MAX6823LUK+T MAX6823MUK+T MAX6823RUK+T MAX6823SUK+T MAX6823VUK+T MAX6823WUK+T MAX6823YUK+T MAX6823ZUK+T MAX6824SUK+T MAX6824WUK+T MAX6825LUK+T MAX6825SUK+T MAX6825TUK+T MAX6824LUK+T MAX6823TUK-T MAX6823TUK+ MAX6823SUK-T MAX6825VUK+T MAX6825RUK+T