4-Pin µp Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay

Transcription

1 ; Rev 3; 12/05 4-Pin µp oltage Monitors with Pin-Selectable General Description The 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 5-powered or 3-powered circuits. The 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 supply voltage falls below a preset threshold, and they keep reset asserted for the pin-selected reset timeout delay after has risen above the reset threshold. The only difference between the two devices is that the has an active-low output (which is guaranteed to be in the correct state for down to 1), while the MAX822 has an active-high output. The reset comparator is designed to ignore fast transients on. Reset thresholds suitable for operation with a variety of supply voltages are available. Low supply current makes the 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 +3 to +5 Power-Supply oltages 2.5µA Supply Current Guaranteed Over Temperature ( C to +125 C) Guaranteed alid to = 1 () Power-Supply Transient Immunity No External Components SOT143 Package Ordering Information PART NOMINAL TH () TOP MARK* LUS-T MUS-T AZ BA PUS-T 4.00 BM TUS-T 3.08 BB SUS-T 2.93 BC UUS-T 2.78 BL RUS-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. Devices are available in both leaded and lead-free packaging. Specify lead-free by replacing -T with +T when ordering. Pin Configuration TOP IEW 20ms 100ms SRT MAX822 () INPUT µp 1 MAX ms () 2 3 SRT ( ) ARE FOR MAX822 ( ) ARE FOR MAX822 SOT143 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 6.0 All Other Inputs...- to ( + ) Input Current,, SRT...20mA Output Current, or...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 ( = full range, T A = C to +125 C, unless otherwise noted. Typical values are at.) Range PARAMETER Supply Current Reset Threshold (Note 1) Reset Threshold Tempco to Reset Delay (Note 1) SRT Input Threshold SYMBOL I CC TH IL IH OPEN T A = 0 C to +70 C T A = C to +85 C MAX82_L/M/P, = 5.5, I OUT = 0 MAX82_R/S/T/U, = 5.5, I OUT = 0 MAX82_L MAX82_M MAX82_P MAX82_T MAX82_S MAX82_U MAX82_R falling at 1m/µs SRT = CONDITIONS Continuous Power Dissipation (T A = +70 C) SOT143-4 (derate 4mW/ C above +70 C)...320mW Operating Temperature Range... C to +125 C Storage Temperature Range C to +160 C Lead Temperature (soldering, 10sec)...+0 C MIN TYP MAX Reset Active Timeout Period t RP SRT = SRT = unconnected SRT = -100 = low for, SRT Input Current (Note 2) SRT = 100 = high for MAX822 SRT = unconnected -1 1 = low for, = high for MAX822 T A = T MIN to T MAX T A = T MIN to T MAX T A = C to +125 C T A = C to +125 C T A = C to +125 C T A = C to +125 C T A = C to +125 C T A = C to +125 C T A = C to +125 C UNITS µa ppm/ C µs ms µa 2

3 ELECTRICAL CHARACTERISTICS (continued) ( = full range, T A = C to +125 C, unless otherwise noted. Typical values are at.) PARAMETER SRT Input Capacitance (Note 3) (see Setting the Reset Timeout Delay section) Output oltage () Output oltage (MAX822) SYMBOL Internal CONDITIONS L/M/P only, I SINK = 3.2mA, = TH(MIN) MIN TYP MAX R/S/T/U only, I SINK = 1.2mA, = TH(MIN) OL T A = 0 C to +70 C, 1 I SINK = 50µA T A = C to +85 C, 1.2 OH OL L/M/P only, I SOURCE = 800µA, TH(MAX) R/S/T/U only, I SOURCE = 500µA, TH(MAX) MAX822L/M only, I SINK = 3.2mA, = TH(MAX) MAX822R/S/T only, I SINK = 1.2mA, = TH(MAX) UNITS pf OH Note 1: output for ; output for MAX822. Note 2: During reset active timeout period only. Note 3: Guaranteed by design. I SOURCE = 150µA, 1.4 TH(MIN) 0.8 Typical Operating Characteristics (, unless otherwise noted.) TIMEOUT PERIOD (ms) SRT = TIMEOUT PERIOD MAX 821/822 TOC-04 TIMEOUT PERIOD (ms) SRT = TIMEOUT PERIOD MAX 821/822 TOC-05 TIMEOUT PERIOD (ms) TIMEOUT PERIOD SRT = UNCONNECTED MAX 821/822 TOC

4 Typical Operating Characteristics (continued) (, unless otherwise noted.) POWER-DOWN DELAY (µs) MAX82_R/S/T POWER-DOWN DELAY FALLING AT 1m/µs FALLING AT 10m/µs MAX 821/822 TOC-02 POWER-DOWN DELAY (µs) MAX82_L/M POWER-DOWN DELAY 60 FALLING AT 1m/µs FALLING AT 10m/µs MAX 821/822 TOC-03 NORMALIZED SUPPLY CURRENT (µa) NORMALIZED THRESHOLD () NORMALIZED THRESHOLD Pin Description PIN MAX822 NAME 1 1 Ground SRT NORMALIZED SUPPLY CURRENT 4 4 Supply oltage MAX 821/822 TOC-01 FUNCTION Active-Low Reset Output. is low while 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. Active-High Reset Output. is high while 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. Set Reset Timeout Input. Connect to for 1ms (max) delay; connect to for 20ms (min) delay; leave unconnected for 100ms (min) delay. MAX 821/822 TOC-07 4

5 Detailed Description 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. The s output is guaranteed to be a logic low for > 1. Once CC exceeds the reset threshold, an internal timer keeps low for the reset timeout period, as determined by the Set Reset Timeout (SRT) input. See the Setting the Reset Timeout Delay section. If a brownout condition occurs ( dips below the reset threshold), goes low. Any time goes below the reset threshold, the internal timer resets to zero, and goes low. The internal timer begins counting after returns above the reset threshold, and remains low for the reset timeout period. The MAX822 has an active-high output that is the inverse of the s output. Setting the Reset Timeout Delay Use the three-level Set Reset Timeout (SRT) input to set the reset timeout delay. Connect SRT to for a 1ms (max) delay; connect it to 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 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) COMPARATOR OERDRIE, TH - (m) Figure 1. Maximum Transient Duration Without Causing a Reset Pulse vs. Comparator Overdrive Applications Information Negative-Going CC Transients While designed to issue a reset to the microprocessor (µp) during power-up, power-down, and brownout conditions, the are relatively immune to short-duration, negative-going transients (glitches). Figure 1 shows the maximum transient duration vs. reset comparator overdrive for which the typically do not generate a reset pulse. This graph was generated using a negative-going pulse applied to, 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 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, a transient that goes 100m 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 can provide additional transient immunity, if desired. /822 FIG-01 5

6 Ensuring a alid Output Down to CC = 0 When falls below 1, the output no longer sinks current it becomes an open circuit. Therefore, high-impedance CMOS logic inputs connected to the output can drift to undetermined voltages. This presents no problem in most applications, since most µp and other circuitry is inoperative with below 1. However, in applications where the output must be valid down to 0, adding a pulldown resistor to the pin will cause any stray leakage currents to flow to ground, holding low (Figure 2a). R1 s value is not critical; 100kΩ is large enough not to load, and small enough to pull to ground. A 100kΩ pull-up resistor to is also recommended for the MAX822 if is required to remain valid for < 1 (Figure 2b). Interfacing to µps with Bidirectional Reset Pins µps with bidirectional reset pins (such as the Motorola 68HC11 series) can contend with the reset output. For example, if the 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 output and the µp reset I/O (Figure 3). Buffer the reset output to other system components. Chip Information TRANSISTOR COUNT: k R1 a) b) BUFFER µp BUFFERED TO OTHER SYSTEM COMPONENTS Figure 3. Interfacing to µps with Bidirectional Reset I/O MAX822 Figure 2. / alid to = Ground Circuit R1 6

7 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-143 4L.EPS PACKAGE OUTLINE, SOT-143, 4L 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. 7 Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.