Ultra-Low-Voltage µp Reset Circuits and Voltage Detectors

Transcription

1 ; Rev 2; 12/05 Ultra-Low-oltage µp Reset Circuits and General Description The microprocessor (µp) supervisory circuits monitor ultra-low-voltage power supplies in µp and digital systems. They provide excellent circuit reliability at low cost by eliminating external components and adjustments when used with +0.9 to +1.5 systems. Factory-trimmed reset thresholds are available for the MAX6841/MAX6842. The / MAX6844/ provide a IN input, allowing the user to externally adjust the reset threshold. The family features a debounced manual reset input (). The reset comparator is designed to ignore fast transients on. The assert a reset signal whenever the supply voltage declines below a preset or adjustable threshold or whenever manual reset () is asserted. Reset remains asserted for a fixed timeout delay after has risen above the reset threshold and when manual reset is deasserted. Five timeout periods are available for each part: 150µs (voltage detector version), 1.5ms, 30ms, 210ms, and 1.68s (typ). The MAX6841/ have an active-low push-pull reset output. The MAX6841/MAX6842/MAX6844 have an active-high push-pull reset output, and the MAX6842/ have an active-low open-drain reset output. The active-low open-drain reset output requires a pullup resistor that can be connected to a voltage from 0 to. The low supply current (5.7µA) and small package (SOT23-5) make the ideal for use in portable equipment. Computers Controllers Intelligent Instruments Critical µp and µc Power Monitoring Portable/Battery-Powered Equipment Telecom/Networking Equipment Basestations Servers/Workstations Applications Selector Guide and Typical Operating Circuit appear at end of data sheet. Features Factory-Set Reset Threshold oltages for Monitoring Supplies from 0.9 to 1.5 (MAX6841/MAX6842) Adjustable Threshold IN (/MAX6844/) Low Power Consumption: 5.7µA (typ) ±2.5% Reset Threshold Accuracy Over Temperature Five Timeout Periods: 150µs (oltage Detector ersion), 1.5ms, 30ms, 210ms, and 1.68s Available in Three Output Configurations Push-Pull Push-Pull Open-Drain Guaranteed Reset alid to = 0.55 (Active Low) Manual Reset Input Immune to Short Transients Space-Saving 5-Pin SOT23 Package Ordering Information PART TEMP RANGE PIN-PACKAGE MAX6841_UKD_-T -40 C to +85 C 5 SOT23-5 MAX6842_UKD_-T -40 C to +85 C 5 SOT23-5 UKD_-T -40 C to +85 C 5 SOT23-5 MAX6844UKD_-T -40 C to +85 C 5 SOT23-5 UKD_-T -40 C to +85 C 5 SOT23-5 Note: Insert desired suffix letter (from the Threshold Suffix Guide and the Active Timeout Period tables) into the blanks to complete the part number. For example, the MAX6842GUKD1 has a reset threshold of 1.11 and a typical reset timeout period of 1.5ms. Sample stock is generally available on standard versions only (see the Standard ersions table). Standard versions require a minimum order increment of 2.5k units. Nonstandard versions must be ordered in 10k-unit increments. Contact factory for availability. All parts are offered in tape-and-reel only. Devices are available in both leaded and lead-free packaging. Specify lead-free by replacing -T with +T when ordering. TOP IEW 1 5 MAX MAX SOT23-5 Pin Configurations () IN MAX SOT23-5 ( ) ARE FOR 6844 Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at , or visit Maxim s website at

2 ABSOLUTE MAXIMUM RATINGS Terminal oltage (with respect to ) to +6, IN, (open-drain) to +6 Push-Pull and to ( + 0.3) Input Current (all pins)...20ma Output Current (, )...20mA 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 Continuous Power Dissipation (T A = +70 C) 5-Pin SOT23 (derate 7.1mW/ C above +70 C)...571mW Operating Temperature Range C to +85 C Junction Temperature C Storage Temperature Range C to +150 C Lead Temperature (soldering, 10s) C ( = to +1.8, T A = -40 C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS / Supply oltage Range MAX6841/MAX6842/MAX6844 (Note 2) = 0.9, no load, reset not asserted Supply Current I CC = 1.5, no load, reset not asserted = 1.8, no load, reset not asserted µa Reset Threshold ( Falling) TH I H G F E D, T A = 0 C to +85 C IN Threshold RSTIN /MAX6844/ (Note 3) m IN Leakage Current I RSTIN na Reset Threshold Hysteresis HYS 0.75 % TH or IN to Reset Delay Reset Active Timeout Period Input oltage (Note 3) t RP falling, step signal from ( TH + 10%) to ( TH - 10%) within 1µs D0 (voltage detector) µs D D D D IL 0.3 IH 0.7 Minimum Input Pulse Width driven from to 0 (Note 3) 1 µs Glitch Rejection driven from to 0 (Note 3) 150 ns to Reset Delay driven from to 0 (Note 3) 500 ns Pullup Resistance to kω ms 2

3 ELECTRICAL CHARACTERISTICS (continued) ( = to +1.8, T A = -40 C to +85 C, unless otherwise noted. Typical values are at T A = +25 C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Open-Drain Output oltage Open-Drain Output Leakage Current Push-Pull Output oltage Push-Pull Output oltage 0.55, I SINK = 10µA, reset asserted 0.2 OL 0.83, I SINK = 80µA, reset asserted 0.2 I LKG > TH, reset not asserted 1 µa 0.55, I SINK = 10µA, reset asserted 0.2 OL 0.83, I SINK = 80µA, reset asserted , I SOURCE = 40µA, reset not OH 0.8 asserted OH OL 0.75, I SOURCE = 10µA, reset asserted 0.83, I SOURCE = 40µA, reset asserted 0.83, I SINK = 80µA, reset not asserted Note 1: 100% production tested at +25 C. Overtemperature limits are guaranteed by design. Note 2: The active-low output has (MIN) = 0.55 (MAX6841/MAX6842). Note 3: For > 0.788, T A = 0 C to +85 C, and for > 0.833, T A = -40 C to +85 C. ( = 1.5, T A = +25 C, unless otherwise noted.) Typical Operating Characteristics SUPPLY CURRENT (µa) SUPPLY CURRENT = 1.8 = 1.5 = MAX toc01 POWER-DOWN DELAY (µs) POWER-DOWN DELAY OD = 10m OD = 20m 100 OD = 100m 50 OD = OERDRIE (m) 0 MAX toc02 NORMALIZED TIMEOUT PERIOD NORMALIZED TIMEOUT PERIOD D2 OPTION D3 OPTION D4 OPTION 0.94 MAX toc03 3

4 Typical Operating Characteristics (continued) ( = 1.5, T A = +25 C, unless otherwise noted.) NORMALIZED CC THRESHOLD NORMALIZED THRESHOLD TH = MAX toc04 NORMALIZED IN THRESHOLD NORMALIZED IN THRESHOLD MAX toc05 POWER-UP/POWER-DOWN CHARACTERISTICS (AUKD3) MAX toc06 200ms/div 1/div 1/div Pin Description MAX6841 MAX6842 PIN MAX6844 NAME FUNCTION 1 Push-Pull (MAX6841) or Open-Drain (MAX6842) Active-Low Reset Output. changes from high to low when drops below the selected reset threshold or is pulled low. remains low for the reset timeout period after exceeds the device reset threshold and is released high. Push-Pull () or Open-Drain () Active-Low Reset Output. 1 changes from high to low when IN drops below the 187.4m reset threshold (referenced to ) or is pulled low. remains low for the reset timeout period after IN exceeds the reset threshold and is released high Ground IN Push-Pull Active-High Reset Output. changes from low to high when input drops below the selected reset threshold or is pulled low. remains high for the reset timeout period after exceeds the device reset threshold and is released high. Push-Pull Active-High Reset Output. changes from low to high when the IN input drops below the 187.4m reset threshold (referenced to ). remains high for the reset timeout period after IN exceeds the reset threshold. Adjustable Reset Input. High-impedance input for reset comparator. Connect this pin to an external resistive-divider network to set the reset threshold voltage; the typical threshold is 187.4m (referenced to ). The /MAX6844/ assert a reset signal when the to IN differential falls below its threshold voltage. Active-Low Manual Reset Input. Internal 20kΩ pullup to. Pull low to force a reset. Reset remains active as long as is low and for the reset timeout period after goes high. Leave unconnected or connect to if unused Supply oltage. Monitored supply for the MAX6841/MAX

5 REF PULLUP Detailed Description Reset Output A microprocessor s (µp s) reset input starts the µp in a known state. The assert a reset during power-up, power-down, and brownout conditions. When the supply voltage falls below a preset threshold (MAX6841/MAX6842) or IN falls below the adjustable threshold (/MAX6844/), reset asserts and stays asserted for a fixed timeout delay (Table 2) after or IN has risen above the reset threshold. The are available with five typical timeout options for each part: 150µs (voltage detector), 1.5ms, 30ms, 210ms, and 1.68s. The MAX6841/MAX6842 have two reset outputs ( and ); one is the inverse of the other. The MAX6841 has one active-high push-pull output and one active-low push-pull output. The MAX6842 has one active-high push-pull output and one active-low opendrain output. The features an active-low push-pull output. The MAX6844 features an activehigh push-pull output, and the has an activelow open-drain output stage. Connect a pullup resistor from the open-drain output to any voltage between 0 and 6. MANUAL DETECT TIMEOUT PERIOD MAX6841 MAX6842 OUTPUT IN Functional Diagrams Manual Reset Input Many µp-based systems require a manual reset capability, allowing the operator, a test technician, or external logic circuitry to initiate a reset. Reset remains asserted while is low, and for a fixed timeout delay after returns high. This input has an internal 20kΩ pullup resistor, so it can be left open if it is not used. can be driven with CMOS logic level or with opendrain/collector outputs. To create a manual reset function, connect a normally open momentary switch from to ground; external debounce circuitry is not required. If is driven from long cables or the device is used in a noisy environment, connect a 0.1µF capacitor from to ground to provide additional noise immunity. IN The /MAX6844/ feature a IN input, which allows users to adjust the reset threshold voltage. The internal reference voltage is 187.4m with respect to. An external resistive-divider network can be used to set voltage monitoring thresholds, as shown in Figure 1. The resistive-divider network must be referenced to. As falls, the voltage at R1 R2 R1 = REF = 187.4m R2 -TH REF - 1 PULLUP IN MAX6844 MANUAL DETECT TIMEOUT PERIOD WHERE REF = 187.4m (WITH RESPECT TO ) AND -TH IS THE THRESHOLD. MAX6844 OUTPUT () ( ) ARE FOR MAX6844 Figure 1. Setting the Adjustable Threshold Externally 5

6 IN decreases. The /MAX6844/ assert a reset when the voltage at IN falls below the IN threshold ( RSTIN ). The lowleakage current at IN allows for relatively largevalue resistors to be used, which reduces power consumption. For example, for -TH = 0.9, if R2 = 100kΩ, then R1 = 26.3kΩ. Applications Information CC Falling Transients The are relatively immune to shortduration falling transients (glitches). Figure 2 shows typical transient duration vs. reset comparator overdrive, for which the do not generate a reset pulse. The graph was generated using a falling pulse applied to, starting 0.1 above the actual reset threshold and ending below it by the magnitude indicated (reset comparator overdrive). The graph indicates the maximum pulse width that a falling transient can have without causing a reset pulse. As the magnitude of the transient increases (goes further below the reset threshold), the maximum allowable pulse width decreases. A 0.1µF bypass capacitor mounted as close as possible to the pin provides additional transient immunity. Ensuring a alid Reset Output Down to CC = 0 When falls below 0.55, the MAX6841/ push-pull output no longer sinks current; it becomes an open circuit. Therefore, high-impedance CMOS-logic inputs connected to can drift to undetermined voltages. This presents no problem in MAXIMUM TRANSIENT DURATION (µs) MAXIMUM TRANSIENT DURATION vs. OERDRIE OCCURS ABOE THIS LINE OERDRIE TH - (m) Figure 2. Maximum Transient Duration vs. Overdrive most applications, because most µp and other circuitry are inoperative with lower than However, in applications in which must be valid down to 0, adding a pulldown resistor to causes any stray leakage currents to flow to ground, holding low (Figure 3). R3 s value is not critical; 200kΩ is large enough not to load and small enough to pull to ground. MAX6841 Figure 3. alid to = 0 A 200kΩ pullup resistor to is also recommended for the MAX6841/MAX6842/MAX6844 if push-pull is required to remain valid for Interfacing to µps with Bidirectional Reset Pins Because the output on the MAX6842/ is open drain, these devices interface easily with µps that have bidirectional reset pins. Connecting the µp supervisor s output directly to the µp s pin with a single pullup resistor allows either device to assert reset (Figure 4). MAX6842 R3 INPUT Figure 4. Interfacing to Microprocessors with Bidirectional Reset I/0 µp 6

7 0.9 MAX6842 Using the MAX6842/ Open-Drain Output with Multiple Supplies Generally, the pullup connected to the MAX6842/ connects to the supply voltage being monitored at the IC s pin. However, some systems use the open-drain output to level-shift from the monitored supply to reset circuitry powered by some other supply (Figure 5). Note that as the MAX6842/ s decreases, so does the IC s ability to sink current at. Also, with any pullup, is pulled high as CC decays toward 0. The voltage where this occurs depends on the pullup resistor value and the voltage to which it is connected. TRANSISTOR COUNT: 788 PROCESS: BiCMOS R PULLUP +5.0 µp Figure 5. Using the MAX6842/ Open-Drain Output with Multiple Supplies Chip Information Table 1. Threshold Suffix Guide SUFFIX THRESHOLD () I H G F E D Table 2. Active Timeout Period Guide SUFFIX ACTIE TIMEOUT PERIOD (ms) MIN TYP MAX D D D D D Table 3. Standard ersions DEICE TOP MARK MAX6841HUKD0 AEDR MAX6841HUKD3 AEDS MAX6841FUKD0 AEDP MAX6841FUKD3 AEDQ MAX6841DUKD0 AEDN MAX6841DUKD3 AEDO MAX6842HUKD0 AEDX MAX6842HUKD3 AEDY MAX6842FUKD0 AED MAX6842FUKD3 AEDW MAX6842DUKD0 AEDT MAX6842DUKD3 AEDU UKD0 AEDZ UKD3 AEA MAX6844UKD0 AEEB MAX6844UKD3 AEEC UKD0 AEAX UKD3 AEAY 7

8 IN 3.3 PART MANUAL ADJUSTABLE INPUT PUSH-PULL PUSH-PULL Selector Guide OPEN-DRAIN MAX6841 MAX6842 MAX6844 DC/DC CONERTER Typical Operating Circuit 0.9 CORE SUPPLY I/O SUPPLY MAX6842D/E µp PUSHBUTTON SWITCH 8

9 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 SOT-23 5L.EPS PACKAGE OUTLINE, SOT-23, 5L 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.