LP3470 Tiny Power On Reset Circuit General Description The LP3470 is a micropower CMOS voltage supervisory circuit designed to monitor power supplies in microprocessor (µP) and other digital systems. It provides maximum adjustability for power-on-reset (POR) and supervisory functions. It is available in the following six standard reset threshold voltage (VRTH) options: 2.63V, 2.93V, 3.08V, 4.00V, 4.38V, and 4.63V. If other voltage options between 2.4V and 5.0V are desired please contact your National Semiconductor representative. The LP3470 asserts a reset signal whenever the VCC supply voltage falls below a reset threshold. The reset time-out period is adjustable using an external capacitor. Reset remains asserted for an interval (programmed by an external capacitor) after VCC has risen above the threshold voltage. The device is available in the tiny SOT23-5 package. Key Specifications n ± 1% Reset Threshold Accuracy Over Temperature n Standard Reset Threshold Voltages: 2.63V, 2.93V, 3.08V, 4.00V, 4.38V, and 4.63V n Custom Reset Threshold Voltages: For other voltages between 2.4V and 5.0V contact your National Semiconductor representative n Very Low Quiescent Current (16 µA typical) n Guaranteed Reset valid down to VCC=0.5V Features n Tiny SOT23-5 Package n Open Drain Reset Output n Programmable Reset Timeout Period Using an External Capacitor n Immune to Short VCC Transients Applications n n n n Critical µP and µC Power Monitoring Intelligent Instruments Computers Portable/Battery-Powered Equipments Pin Configuration and Basic Operating Circuit Pin Configuration Basic Operating Circuit DS100016-2 Top View See NS Package Number MA05B DS100016-1 © 1999 National Semiconductor Corporation DS100016 www.national.com LP3470 Tiny Power On Reset Circuit June 1999 Ordering Information Operating Temperature Range −20˚C to +85˚C −40˚C to +85˚C www.national.com Order Number Nominal VRTH (V) Package Marking Package Type Supplied As LP3470M5-2.63 2.63 D25B SOT23-5 250 Units on Tape and Reel LP3470M5X-2.63 2.63 D25B SOT23-5 3k Units on Tape and Reel LP3470M5-2.93 2.93 D26B SOT23-5 250 Units on Tape and Reel LP3470M5X-2.93 2.93 D26B SOT23-5 3k Units on Tape and Reel LP3470M5-3.08 3.08 D28B SOT23-5 250 Units on Tape and Reel LP3470M5X-3.08 3.08 D28B SOT23-5 3k Units on Tape and Reel LP3470M5-4.00 4.00 D29B SOT23-5 250 Units on Tape and Reel LP3470M5X-4.00 4.00 D29B SOT23-5 3k Units on Tape and Reel LP3470M5-4.38 4.38 D30B SOT23-5 250 Units on Tape and Reel LP3470M5X-4.38 4.38 D30B SOT23-5 3k Units on Tape and Reel LP3470M5-4.63 4.63 D31B SOT23-5 250 Units on Tape and Reel LP3470M5X-4.63 4.63 D31B SOT23-5 3k Units on Tape and Reel LP3470IM5-2.63 2.63 D25C SOT23-5 250 Units on Tape and Reel LP3470IM5X-2.63 2.63 D25C SOT23-5 3k Units on Tape and Reel LP3470IM5-2.93 2.93 D26C SOT23-5 250 Units on Tape and Reel LP3470IM5X-2.93 2.93 D26C SOT23-5 3k Units on Tape and Reel LP3470IM5-3.08 3.08 D28C SOT23-5 250 Units on Tape and Reel LP3470IM5X-3.08 3.08 D28C SOT23-5 3k Units on Tape and Reel LP3470IM5-4.00 4.00 D29C SOT23-5 250 Units on Tape and Reel LP3470IM5X-4.00 4.00 D29C SOT23-5 3k Units on Tape and Reel LP3470IM5-4.38 4.38 D30C SOT23-5 250 Units on Tape and Reel LP3470IM5X-4.38 4.38 D30C SOT23-5 3k Units on Tape and Reel LP3470IM5-4.63 4.63 D31C SOT23-5 250 Units on Tape and Reel LP3470IM5X-4.63 4.63 D31C SOT23-5 3k Units on Tape and Reel 2 Absolute Maximum Ratings (Note 1) Operating Temperature Range LP3470 LP3470I Junction Temperature (TJmax) Power Dissipation (TA = 25˚C) (Note 2) θJA (Note 2) Storage Temp. Range Lead Temp. (Soldering, 5 sec) ESD Rating (Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VCC Voltage Reset Voltage Output Current (Reset) −0.3V to +6V −0.3V to +6V 10 mA −20˚C to +85˚C −40˚C to +85˚C 125˚C 300 mW 280˚C/W −65˚C to +150˚C 260˚C 2 kV Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range, unless otherwise specified. VCC = +2.4V to +5.0V unless otherwise noted. Symbol Parameter Conditions Typ (Note 4) Min (Note 5) Max (Note 5) 0.5 5.5 V 30 µA VCC Operating Voltage Range ICC VCC Supply Current VCC = 4.5V VRTH Reset Threshold Voltage (Note 6) LP3470 VRTH 0.99 VRTH 0.99 VRTH 1.01 VRTH 1.01 VRTH LP3470I VRTH 0.99 VRTH 0.985 VRTH 1.01 VRTH 1.015 VRTH 35 15 VHYST Hysteresis Voltage (Note 7) tPD VCC to Reset Delay VCC falling at 1 mV/µs tRP Reset Timeout Period (Note 8) C1 = 1 nF VOL Reset Output Voltage Low R1 External Pull-up Resistor ILEAK Reset Output Leakage Current 16 100 2 1.0 65 mV µs 3.5 VCC = 0.5V; IOL = 30 µA 0.1 0.1 VCC =VRTH −100 mV; IOL = 4 mA 0.4 20 0.68 V 300 VCC = 1.0V; IOL = 100 µA 0.15 Units ms V 68 kΩ 1 µA 6 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device beyond its operating conditions. Note 2: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJmax (Maximum Junction Temperature), θJA (Junction to Ambient Thermal Resistance), and TA (Ambient Temperature). The maximum allowable power dissipation at any temperature is PDmax = (TJmax − TA)/ θJA or the number given in the Absolute Maximum Ratings, whichever is lower. Note 3: The Human Body Model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 4: Typical numbers are at 25˚C and represent the most likely parametric norm. Note 5: Min. and Max. limits in standard typeface are 100% production tested at 25˚C. Min. and Max. limits in boldface are guaranteed through correlation using Statistical Quality Control (SQC) methods. The limits are used to calculate National’s Average Outgoing Quality Level (AOQL). Note 6: Factory-trimmed reset thresholds are available in 50 mV increments from 2.4V to 5.0V. Contact your National Semiconductor representative. Note 7: VHYST affects the relation between VCC and Reset as shown in the timing diagram. Note 8: tRP is programmable by varying the value of the external capacitor (C1) connected to pin SRT. The equation is: tRP = 2000 x C1 (C1 in µF and tRP in ms). 3 www.national.com Typical Operating Characteristics ICC vs Temperture TA = +25˚C, unless otherwise specified. ICC vs VCC VCC to Reset Delay vs Temp DS100016-10 DS100016-13 DS100016-11 Normalized tRP vs Temp. Normalized VRTH vs Temp. DS100016-12 Transient Rejection DS100016-8 DS100016-6 VHYST vs VRTH VHYST vs Temperature DS100016-9 DS100016-14 Pin Description Pin Name Function 1 SRT Set Reset Time-out Input. Connect a capacitor between this input and ground to select the Reset Time-out period (tRP). tRP = 2000 x C1 (C1 in µF and tRP in ms). If no capacitor is connected, leave this pin floating. 2 GND Ground pin. 3 VCC1 Always connect to pin VCC (Pin 4). 4 VCC Supply voltage, and reset threshold monitor input. 5 Reset www.national.com Open-Drain, Active-Low reset output. Connect to an external pull-up resistor. Reset changes from high to low whenever the monitored voltage (VCC) drops below the reset threshold voltage (VRTH). Once VCC exceeds VRTH, Reset remains low for the reset timeout period (tRP) and then goes high. 4 Functional Block Diagram DS100016-3 Pull-up Resistor Selection The LP3470’s Reset output structure is a simple open-drain N-channel MOSFET switch. A pull-up resistor (R1) should be connected to VCC. R1 should be large enough to limit the current through the output MOSFET (Q1) below 10 mA. A resistor value of more than 680Ω guarantees this. R1 should also be small enough to ensure a logic high while supplying all the leakage current through the Reset pin. A resistor value of less than 68kΩ satisfies this condition. A typical pull-up resistor value of 20 kΩ is sufficient in most applications. Application Information Reset Timeout Period The Reset Timeout Period (tRP) is programmable using an external capacitor (C1) connected to pin SRT of LP3470. A Ceramic chip capacitor rated at or above 10V is sufficient. The Reset Timeout Period (tRP) can be calculated using the following formula: tRP (ms) = 2000 x C1 (µF). For example a C1 of 100 nF will achieve a tRP of 200 ms. If no delay due to tRP is needed in a certain application, the pin SRT should be left floating. Negative-Going VCC Transients The LP3470 is relatively immune to short duration negative-going VCC transients (glitches). The Typical Operating Characteristics show the Maximum Transient Duration vs. Negative Transient Amplitude (graph titled Transient Rejection), for which reset pulses are not generated. This graph shows the maximum pulse width a negative-going VCC transient may typically have without causing a reset pulse to be issued. As the transient amplitude increases (i.e. goes farther below the reset threshold), the maximum allowable pulse width decreases. A 0.1 µF bypass capacitor mounted close to VCC provides additional transient immunity. Reset Output In applications like microprocessor (µP) systems, errors might occur in system operation during power-up, power-down, or brownout conditions. It is imperative to monitor the power supply voltage in order to prevent these errors from occurring. The LP3470 asserts a reset signal whenever the VCC supply voltage is below a threshold (VRTH) voltage. Reset is guaranteed to be a logic low for VCC > 0.5V. Once VCC exceeds the reset threshold, the reset is kept asserted for a time period (tRP) programmed by an external capacitor (C1); after this interval Reset goes to logic high. If a brownout condition occurs (monitored voltage falls below the reset threshold minus a small hysteresis), Reset goes low. When VCC returns above the reset threshold, Reset remains low for a time period tRP before going to logic high. 5 www.national.com Timing Diagram DS100016-4 Typical Application Circuit DS100016-5 www.national.com 6 LP3470 Tiny Power On Reset Circuit Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead Small Outline Package (M5) For Ordering Information See Ordering Information Table In This Data Sheet NSPackage Number MA05B LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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