19-1122; Rev 1; 12/99 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay The MAX821/MAX822 microprocessor (µP) supervisory circuits monitor power supplies in µP and digital systems. They provide excellent circuit reliability and low cost by eliminating external components and adjustments when used with 5V-powered or 3V-powered circuits. The MAX821/MAX822 also provide a power-on reset timeout delay that is pin selectable to 1ms (max), 20ms (min), or 100ms (min). These devices perform a single function: they assert a reset signal whenever the V CC supply voltage falls below a preset threshold, and they keep reset asserted for the pin-selected reset timeout delay after VCC has risen above the reset threshold. The only difference between the two devices is that the MAX821 has an active-low RESET output (which is guaranteed to be in the correct state for V CC down to 1V), while the MAX822 has an active-high RESET output. The reset comparator is designed to ignore fast transients on VCC. Reset thresholds suitable for operation with a variety of supply voltages are available. Low supply current makes the MAX821/MAX822 ideal for use in portable equipment. These devices come in a 4-pin SOT143 package. ________________________Applications Bar-Code Scanners Computers Controllers Intelligent Instruments Critical µP and µC Power Monitoring Portable/Battery-Powered Equipment __________Typical Operating Circuit Features ♦ Pin-Selectable, Precision Power-On Reset Delay: 1ms (max), 20ms (min), or 100ms (min) ♦ Precision Monitoring of +3V to +5V Power-Supply Voltages ♦ 2.5µA Supply Current ♦ Guaranteed Over Temperature (-40°C to +125°C) ♦ Guaranteed RESET Valid to VCC = 1V (MAX821) ♦ Power-Supply Transient Immunity ♦ No External Components ♦ SOT143 Package Ordering Information PART NOMINAL VTH (V) TOP MARK* MAX821LUS-T 4.63 AZ_ _ MAX821MUS-T 4.38 BA_ _ MAX821PUS-T 4.00 BM_ _ MAX821TUS-T 3.08 BB_ _ MAX821SUS-T 2.93 BC_ _ MAX821UUS-T 2.78 BL_ _ MAX821RUS-T 2.63 BD_ _ MAX822LUS-T 4.63 BF_ _ MAX822MUS-T 4.38 BG_ _ MAX822TUS-T 3.08 BH_ _ MAX822SUS-T 2.93 BJ_ _ MAX822RUS-T 2.63 BK_ _ * The first two letters in the package top mark identify the part, while the remaining two letters are the lot-tracking code. Note: These parts are offered in the SOT143-4 package, in the extended temperature range (-40°C to +85°C). Pin Configuration 20ms 100ms 1ms VCC VCC MAX821 MAX822 µP TOP VIEW RESET (RESET) SRT GND 4 VCC 3 SRT MAX821 MAX822 RESET INPUT (RESET) RESET GND 1 2 GND SOT143 ( ) ARE FOR MAX822 ( ) ARE FOR MAX822 ________________________________________________________________ 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 1-800-835-8769. MAX821/MAX822 General Description MAX821/MAX822 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay ABSOLUTE MAXIMUM RATINGS Terminal Voltage (with respect to GND) VCC ......................................................................-0.3V to 6.0V All Other Inputs.......................................-0.3V to (VCC + 0.3V) Input Current, VCC, SRT......................................................20mA Output Current, RESET or RESET .......................................20mA Continuous Power Dissipation (TA = +70°C) SOT143-4 (derate 4mW/°C above +70°C)...................320mW Operating Temperature Range .........................-40°C to +125°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 = full range, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL VCC Range Supply Current ICC CONDITIONS 1.0 5.5 1.2 5.5 MAX82_L/M/P, VCC = 5.5V, IOUT = 0 TA = +25°C MAX82_R/S/T/U, VCC = 5.5V, IOUT = 0 TA = +25°C MAX82_P MAX82_T MAX82_S MAX82_U MAX82_R Reset Active Timeout Period SRT Input Current (Note 2) VIL SRT Input Threshold VIH VOPEN 2 7.0 1.8 5.5 12 TA = TMIN to TMAX TA = +25°C 4.56 TA = -40°C to +125°C 4.50 TA = +25°C 4.31 TA = -40°C to +125°C 4.25 TA = +25°C 3.97 TA = -40°C to +125°C 3.91 TA = +25°C 3.04 TA = -40°C to +125°C 3.00 TA = +25°C 2.89 TA = -40°C to +125°C 2.85 TA = +25°C 2.74 TA = -40°C to +125°C 2.70 TA = +25°C 2.59 TA = -40°C to +125°C 2.55 4.63 V µA 4.70 4.75 4.38 4.45 4.50 4.00 4.04 4.09 3.08 3.11 3.15 2.93 V 2.96 3.00 2.78 2.81 2.85 2.63 2.66 2.70 30 ppm/°C 50 µs SRT = GND 0.5 0.8 1 SRT = VCC 20 32 40 SRT = unconnected 100 160 200 SRT = GND RESET = low for MAX821, SRT = VCC RESET = high for MAX822 SRT = unconnected -100 RESET = low for MAX821, RESET = high for MAX822 UNITS 9 VCC falling at 1mV/µs tRP 2.5 TA = TMIN to TMAX Reset Threshold Tempco VCC to Reset Delay (Note 1) MAX TA = -40°C to +85°C MAX82_M VTH TYP TA = 0°C to +70°C MAX82_L Reset Threshold (Note 1) MIN 100 -1 ms µA 1 0.07VCC V 0.9VCC 0.5VCC _______________________________________________________________________________________ 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay (VCC = full range, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS SRT Input Capacitance (Note 3) (see Setting the Reset Timeout Delay section) VOL RESET Output Voltage (MAX821) MAX UNITS Internal 20 pF MAX821L/M/P only, ISINK = 3.2mA, VCC = VTH(MIN) 0.4 MAX821R/S/T/U only, ISINK = 1.2mA, VCC = VTH(MIN) 0.3 ISINK = 50µA VOH VOL RESET Output Voltage (MAX822) MIN TA = 0°C to +70°C, VCC ≥ 1V 0.3 TA = -40°C to +85°C, VCC ≥ 1.2V 0.3 V MAX821L/M/P only, ISOURCE = 800µA, VCC ≥ VTH(MAX) VCC -1.5 MAX821R/S/T/U only, ISOURCE = 500µA, VCC ≥ VTH(MAX) 0.8VCC MAX822L/M only, ISINK = 3.2mA, VCC = VTH(MAX) 0.4 MAX822R/S/T only, ISINK = 1.2mA, VCC = VTH(MAX) 0.3 ISOURCE = 150µA, 1.4V ≤ VCC ≤ VTH(MIN) VOH TYP V 0.8VCC Note 1: RESET output for MAX821; RESET output for MAX822. Note 2: During reset active timeout period only. Note 3: Guaranteed by design. __________________________________________Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) 0.8 0.7 0.6 SRT = VCC 35 34 33 32 31 -20 0 20 40 60 TEMPERATURE (°C) 80 100 SRT = UNCONNECTED 175 170 165 160 155 150 30 -40 180 MAX 821/822 TOC-06 0.9 36 MAX 821/822 TOC-05 SRT = GND RESET TIMEOUT PERIOD (ms) MAX 821/822 TOC-04 1.0 RESET TIMEOUT PERIOD (ms) RESET TIMEOUT PERIOD vs. TEMPERATURE RESET TIMEOUT PERIOD vs. TEMPERATURE RESET TIMEOUT PERIOD (ms) RESET TIMEOUT PERIOD vs. TEMPERATURE -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) _______________________________________________________________________________________ 3 MAX821/MAX822 ELECTRICAL CHARACTERISTICS (continued) ____________________________Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX82_L/M POWER-DOWN RESET DELAY vs. TEMPERATURE MAX82_R/S/T POWER-DOWN RESET DELAY vs. TEMPERATURE 35 VCC FALLING AT 1mV/µs 30 25 20 15 VCC FALLING AT 10mV/µs 10 5 60 MAX 821/822 TOC-03 40 POWER-DOWN RESET DELAY (µs) MAX 821/822 TOC-02 POWER-DOWN RESET DELAY (µs) 45 VCC FALLING AT 1mV/µs 50 40 30 20 VCC FALLING AT 10mV/µs 10 0 0 -40 -20 0 20 40 60 80 -40 100 -20 0 20 40 60 80 100 TEMPERATURE (°C) TEMPERATURE (°C) NORMALIZED RESET THRESHOLD vs. TEMPERATURE NORMALIZED SUPPLY CURRENT vs. TEMPERATURE 1.05 1.00 0.95 MAX 821/822 TOC-07 NORMALIZED RESET THRESHOLD (V) 1.003 MAX 821/822 TOC-01 1.10 NORMALIZED SUPPLY CURRENT (µA) MAX821/MAX822 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay 1.002 1.001 1.000 0.999 0.998 0.997 0.90 -40 -20 0 20 40 60 80 100 -40 -20 0 20 40 60 80 100 TEMPERATURE (°C) TEMPERATURE (°C) ______________________________________________________________Pin Description PIN 4 NAME FUNCTION MAX821 MAX822 1 1 GND 2 – RESET Active-Low Reset Output. RESET is low while VCC is below the reset threshold. It remains low for the reset timeout period after the reset condition is terminated. The reset timeout period is determined by the SRT input. – 2 RESET Active-High Reset Output. RESET is high while VCC is below the reset threshold. It remains high for the reset timeout period after the reset condition is terminated. The reset timeout period is determined by the SRT input. 3 3 SRT Set Reset Timeout Input. Connect to GND for 1ms (max) delay; connect to VCC for 20ms (min) delay; leave unconnected for 100ms (min) delay. 4 4 VCC Supply Voltage Ground _______________________________________________________________________________________ 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay If a brownout condition occurs (VCC dips below the reset threshold), RESET goes low. Any time VCC goes below the reset threshold, the internal timer resets to zero, and RESET goes low. The internal timer begins counting after VCC returns above the reset threshold, and RESET remains low for the reset timeout period. The MAX822 has an active-high RESET output that is the inverse of the MAX821’s RESET output. Setting the Reset Timeout Delay Use the three-level Set Reset Timeout (SRT) input to set the reset timeout delay. Connect SRT to GND for a 1ms (max) delay; connect it to VCC for a 20ms (min) delay; or leave it unconnected for a 100ms (min) delay. If you choose to drive the SRT pin with an external signal, make sure the signal source can charge/discharge the capacitance on SRT quickly enough (<500µs) to avert an unintended reset timeout delay. To ensure proper operation when selecting the 100ms timeout (SRT = unconnected), minimize capacitive loading on the SRT pin (< 200pF). Excessive capacitive loading can select an unintended faster timeout mode. Reset Threshold Accuracy The MAX821/MAX822 are designed to meet their worstcase specifications over their entire operating temperature range. Choose a reset threshold guaranteed to assert at a voltage below the power supply’s regulation range and above the minimum specified operating voltage range for the system’s ICs. MAXIMUM TRANSIENT DURATION (µs) The MAX821’s RESET output is guaranteed to be a logic low for VCC > 1V. Once VCC exceeds the reset threshold, an internal timer keeps RESET low for the reset timeout period, as determined by the Set Reset Timeout (SRT) input. See the Setting the Reset Timeout Delay section. 300 TA = +25°C 250 MAX821/822 FIG-01 Reset Output A microprocessor’s (µP’s) reset input starts the µP in a known state. These µP supervisory circuits assert reset to prevent code-execution errors during power-up, power-down, or brownout conditions. They also provide a reset timeout delay that is pin programmable to 1ms (max), 20ms (min), or 100ms (min). This feature allows flexibility in designing bar-code scanners, hand-held devices, and other applications that require quick or nonstandard power-up times. MAX821/MAX822 _______________Detailed Description 200 150 100 50 0 1 10 100 1000 RESET COMPARATOR OVERDRIVE, VTH-VCC (mV) Figure 1. Maximum Transient Duration Without Causing a Reset Pulse vs. Comparator Overdrive __________Applications Information Negative-Going VCC Transients While designed to issue a reset to the microprocessor (µP) during power-up, power-down, and brownout conditions, the MAX821/MAX822 are relatively immune to short-duration, negative-going VCC transients (glitches). Figure 1 shows the maximum transient duration vs. reset comparator overdrive for which the MAX821/MAX822 typically do not generate a reset pulse. This graph was generated using a negative-going pulse applied to VCC, starting above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). The graph indicates the typical maximum pulse width a negative-going VCC transient may have without causing a reset pulse to be issued. As the magnitude of the transient increases (goes farther below the reset threshold), the maximum allowable pulse width decreases. Typically, for the MAX821/MAX822, a VCC transient that goes 100mV below the reset threshold and lasts 12µs or less will not cause a reset pulse to be issued. A 0.1µF capacitor mounted as close as possible to VCC can provide additional transient immunity, if desired. _______________________________________________________________________________________ 5 MAX821/MAX822 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay Ensuring a Valid RESET Output Down to VCC = 0V When VCC falls below 1V, the MAX821 RESET output no longer sinks current—it becomes an open circuit. Therefore, high-impedance CMOS logic inputs connected to the RESET output can drift to undetermined voltages. This presents no problem in most applications, since most µP and other circuitry is inoperative with VCC below 1V. However, in applications where the RESET output must be valid down to 0V, adding a pulldown resistor to the RESET pin will cause any stray leakage currents to flow to ground, holding RESET low (Figure 2a). R1’s value is not critical; 100kΩ is large enough not to load RESET, and small enough to pull RESET to ground. A 100kΩ pull-up resistor to VCC is also recommended for the MAX822 if RESET is required to remain valid for VCC < 1V (Figure 2b). VCC VCC VCC VCC R1 MAX822 MAX821 RESET RESET R1 GND GND b) a) Figure 2. RESET/RESET Valid to VCC = Ground Circuit Interfacing to µPs with Bidirectional Reset Pins µPs with bidirectional reset pins (such as the Motorola 68HC11 series) can contend with the MAX821 reset output. For example, if the MAX821 RESET output is asserted high and the µP wants to pull it low, indeterminate logic levels may result. To correct such cases, connect a 4.7kΩ resistor between the MAX821 RESET output and the µP reset I/O (Figure 3). Buffer the reset output to other system components. ___________________Chip Information BUFFER VCC VCC MAX821 RESET GND BUFFERED RESET TO OTHER SYSTEM COMPONENTS 4.7k µP RESET GND TRANSISTOR COUNT: 492 Figure 3. Interfacing to µPs with Bidirectional Reset I/O 6 _______________________________________________________________________________________ 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay SOT1434.EPS _______________________________________________________________________________________ 7 MAX821/MAX822 ________________________________________________________Package Information MAX821/MAX822 4-Pin µP Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay NOTES 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 408-737-7600 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.