LM3722/LM3723/LM3724 5-Pin Microprocessor Reset Circuits General Description Features The LM3722/LM3723/LM3724 microprocessor supervisory circuits monitor the power supplies in microprocessor and digital systems. They provide a reset to the microprocessor during power-up, power-down, brown-out conditions, and manual reset. The LM3722/LM3723/LM3724 asserts a reset signal whenever the supply decreases below the factory-programmed reset threshold for at least 100 ms. The reset signal remains asserted for 190 ms after VCC rises above the threshold. The LM3722 has an active-low RESET push-pull output. The LM3723 has an active-high RESET push-pull output. The LM3724 has an active-low open-drain RESET output. n Precise monitoring of 2.5V, 3.3V, and 5V supply voltages n Fully specified over temperature Industrial: −40˚C to +85˚C Extended: −40˚C to +125˚C n 100 ms minimum Power-On Reset pulse width, 190 ms typical: Active-Low RESET Output (LM3722) Active-High RESET Output (LM3723) Active-Low RESET Open Drain Output (LM3724) n Guaranteed RESET Output valid for VCC ≥ 1V n Low Supply Current, 6µA typical n Power supply transient immunity n Compatible with MAX811/812 applications Three standard reset voltage options are available, suitable for monitoring 5V, 3.3V, and 2.5V supply voltages. Additional reset voltages are also available; contact National Semiconductor for details. With a low supply current of only 6µA, the LM3722/LM3723/LM3724 are ideal for use in portable equipment. The LM3722/LM3723/LM3724 are available in the 5-pin SOT23 package. Applications n n n n n Microprocessor Systems Computers Controllers Intelligent Instruments Portable/Battery-Powered Equipment Typical Application Circuit 20014401 20014437 Connection Diagram SOT23-5 20014402 *( ) are for LM3723 © 2001 National Semiconductor Corporation DS200144 www.national.com LM3722/LM3723/LM3724 5-Pin Microprocessor Reset Circuits June 2001 LM3722/LM3723/LM3724 Ordering Information Industrial Temperature Range (−40˚C to +85˚C): Reset Threshold (V) LM3722 Supplied as 1000 units, tape & reel LM3722 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3722IM5-4.63 LM3722IM5X-4.63 R43B 3.08 LM3722IM5-3.08 LM3722IM5X-3.08 R41B 2.32 LM3722IM5-2.32 LM3722IM5X-2.32 R34B Reset Threshold (V) LM3723 Supplied as 1000 units, tape & reel LM3723 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3723IM5-4.63 LM3723IM5X-4.63 R13B 3.08 LM3723IM5-3.08 LM3723IM5X-3.08 R11B 2.32 LM3723IM5-2.32 LM3723IM5X-2.32 R46B Reset Threshold (V) LM3724 Supplied as 1000 units, tape & reel LM3724 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3724IM5-4.63 LM3724IM5X-4.63 R55B 3.08 LM3724IM5-3.08 LM3724IM5X-3.08 R53B 2.32 LM3724IM5-2.32 LM3724IM5X-2.32 R50B Package Type NSC Package SOT23-5 MF05A Package Type NSC Package SOT23-5 MF05A Package Type NSC Package SOT23-5 MF05A Package Type NSC Package SOT23-5 MF05A Package Type NSC Package SOT23-5 MF05A Package Type NSC Package SOT23-5 MF05A Extended Temperature Range (−40˚C to +125˚C): Reset Threshold (V) LM3722 Supplied as 1000 units, tape & reel LM3722 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3722EM5-4.63 LM3722EM5X-4.63 R56B 3.08 LM3722EM5-3.08 LM3722EM5X-3.08 R57B 2.32 LM3722EM5-2.32 LM3722EM5X-2.32 R58B Reset Threshold (V) LM3723 Supplied as 1000 units, tape & reel LM3723 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3723EM5-4.63 LM3723EM5X-4.63 R59B 3.08 LM3723EM5-3.08 LM3723EM5X-3.08 R60 2.32 LM3723EM5-2.32 LM3723EM5X-2.32 R61B Reset Threshold (V) LM3724 Supplied as 1000 units, tape & reel LM3724 Supplied as 3000 units, tape & reel Package Top Mark 4.63 LM3724EM5-4.63 LM3724EM5X-4.63 R62B 3.08 LM3724EM5-3.08 LM3724EM5X-3.08 R63B 2.32 LM3724EM5-2.32 LM3724EM5X-2.32 R64B Custom voltages and improved accuracies are available, subject to minimum orders. Contact your local National Semiconductor Sales Office for information. www.national.com 2 PIN NAME 1 GND Ground reference 2 GND Ground reference, device substrate, connect to ground. 3 RESET LM3722/LM3724 RESET LM3723 FUNCTION Active-low output. RESET remains low while VCC is below the reset threshold voltage, and for 190 ms after VCC rises above the reset threshold voltage. Active-high output. RESET remains high while VCC is below the reset threshold, and for 190 ms after VCC rises above the reset threshold. 4 MR Active-low input. Reset is asserted whenever this pin is pulled low and remains asserted for 190 ms after the MR pin goes high. May be left open. 5 VCC Supply Voltage (+5V, +3.3V, or +2.5V, nominal) Block Diagram LM3722/LM3723/LM3724 Block Diagram 20014435 3 www.national.com LM3722/LM3723/LM3724 Pin Description LM3722/LM3723/LM3724 Absolute Maximum Ratings (Note 1) Continuous Power Dissipation (TA = +70˚C) SOT-23 (Note 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VCC, MR −0.3V to 6.0V RESET, RESET 320mW Operating Temperature Range −0.3V to (VCC+ 0.3V) Industrial: −40˚C to +85˚C Extended: −40˚C to +125˚C Maximum Junction Temperature Input Current, VCC Pin 20mA Storage Temperature Range Output Current, RESET, RESET Pin 20mA Lead Temperature (soldering, 10sec) ESD Rating (Note 2) 125˚C −65˚C to +160˚C +300˚C 2kV Electrical Characteristics Typical values are at TA = +25˚C. Limits with standard typeface are for TA = +25˚C, and limits in boldface type apply for the operating temperature range (−40˚C to +85˚C) for LM372_IM5X, and (−40˚C to +125˚C) for LM372_EM5X, unless otherwise noted. (Note 4) Symbol VCC ICC VTH VTH Tempco Parameter Conditions VCC Range Supply Current (ILOAD = 0A) Reset Threshold Min 1.0 5.5 V 8 15 µA LM372 _ -3.08 VCC = 3.6V 7 10 LM372 _ -2.32 VCC = 2.5V 6 10 LM372 _ -4.63 4.54 4.50 4.63 4.72 4.75 LM372 _ -3.08 3.03 3.00 3.08 3.14 3.15 LM372 _ -2.32 2.27 2.25 2.32 2.37 2.40 30 VCC to Reset Delay (Note 5) tRP Reset Active Timeout Period 100 tMR MR Minimum Pulse Width 10 tMD MR to Reset Propagation Delay VCC = VTH to (VTH − 100mV) VIH VCC > VTH(MAX), LM372_ -4.63 VIL VCC > VTH(MAX), LM372_ -3.08, LM372_ -2.32 RESET Output Voltage Low (LM3722) VOH RESET Output Voltage High (LM3722) VOL RESET Output Voltage Low (LM3723) www.national.com µs 560 µs 2 µs 100 ns 0.8 0.7 VCC V 0.25 VCC 22 kΩ VCC = VTH min, ISINK = 1.2mA, (LM3722-2.32/3.08) 0.3 VCC = VTH min, ISINK = 3.2mA, (LM3722-4.63) 0.4 VCC > 1V, ISINK = 50µA 0.3 VCC > VTH max, ISOURCE = 500µA, (LM3722-2.32/3.08) 0.8VCC VCC > VTH max, ISOURCE = 800µA, (LM3722-4.63) VCC−1.5 V V VCC = VTH max, ISINK = 1.2mA (LM3723 -2.32/3.08) 0.3 VCC = VTH max, ISINK = 3.2mA (LM3723 -4.63) 0.4 4 ms 2.3 MR Pull-Up Resistance VOL 190 V ppm/˚C 20 MR Glitch Immunity (Note 6) MR Input Threshold Units VCC = 5.5V tRD VIL Max LM372 _ -4.63 Reset Threshold Temperature Coefficient VIH Typ V (Continued) Typical values are at TA = +25˚C. Limits with standard typeface are for TA = +25˚C, and limits in boldface type apply for the operating temperature range (−40˚C to +85˚C) for LM372_IM5X, and (−40˚C to +125˚C) for LM372_EM5X, unless otherwise noted. (Note 4) Symbol Parameter VOH RESET Output Voltage High (LM3723) 1.8V < VCC < VTH min, ISOURCE = 150µA VOL RESET Output Voltage Low (LM3724) VCC = VTH min, ISINK = 1.2 mA (LM3724 -2.32/3.08) 0.3 VCC = VTH min, ISINK = 3.2 mA (LM3724 -4.63) 0.4 VCC > 1V, ISINK = 50µA 0.3 IIN RESET Output Leakage Current (LM3724) Conditions VCC > VTH, RESET = 5.5V Min Typ Max Units V 0.8VCC 0.5 V µA Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which the device operates correctly. Operating ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics. Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. Note 3: At elevated temperatures, devices must be derated based on package thermal resistance. The device in the SOT23-5 package must be derated at 4.5mW/˚C at ambient temperatures above 70˚C. The device has internal thermal protection. Note 4: Production testing done at TA = +25˚C. Limits over the operating temperature range are guaranteed through correlation using Statistical Quality Control (SQC) methods. Note 5: RESET Output for LM3722 and LM3724, RESET output for LM3723. Note 6: Glitches of 100 ns or less typically will not generate a reset pulse. 5 www.national.com LM3722/LM3723/LM3724 Electrical Characteristics LM3722/LM3723/LM3724 Typical Performance Characteristics Supply Current vs VCC Supply Current vs Temperature 20014403 20014407 Reset Timeout vs VCC Reset Timeout vs Temperature 20014408 20014404 Normalized VTH vs Temperature LM3724 VOL vs Current 20014416 www.national.com 20014405 6 LM3722/LM3723/LM3724 Typical Performance Characteristics (Continued) LM3724 Low VCC Characteristics 20014406 7 www.national.com LM3722/LM3723/LM3724 Timing Diagram 20014412 Reset Threshold The LM3722/LM3723/LM3724 are available with reset voltages of 4.63V, 3.08V, and 2.32V which are suitable for monitoring 5.0V, 3.3V, and 2.5V supplies respectively. Other reset thresholds in the 2.20V to 5.0V range, in 10 mV steps, are available; contact National Semiconductor for details. Circuit Information Reset Output The reset input of a µP initializes the device into a known state. The LM3722/LM3723/LM3724 microprocessor voltage monitoring circuits assert a forced reset output to prevent code execution errors during power-up, power-down, and brownout conditions. RESET is guaranteed valid for VCC ≥ 1V. Once VCC exceeds the reset threshold, an internal timer maintains the output for the reset timeout period. After this interval, reset goes high and the microprocessor initializes itself into a known state. The LM3722 and LM3724 offer an active-low RESET; the LM3723 offers an active-high RESET. As VCC drops below the reset threshold (such as during a brownout), the reset activates (see the Negative-Going VCC Transients section). When VCC again rises above the reset threshold, the internal timer starts. Reset holds until VCC exceeds the reset threshold for longer than the reset timeout period. After this time, reset releases. Additionally, the Manual Reset input (MR) will initiate a forced reset. See the Manual Reset Input section. The LM3722/LM3723/LM3724 reset outputs ignore short duration glitches on VCC and MR. See the Applications Information section for details. www.national.com Manual Reset Input (MR) Many µP-based products require a manual reset capability, allowing the operator to initiate a reset. The MR input is fully debounced and provides an internal 22 kΩ pull-up. When the MR input is pulled below VIL (0.25VCC) for more than 100 ns, reset is asserted after a typical delay of 2 µs. Reset remains active as long as MR is held low, and releases after MR rises above VIH and the reset timeout period expires. Use MR with digital logic to assert reset or to daisy chain supervisory circuits. Applications Information Benefits of Precision Reset Thresholds A microprocessor supply supervisor must provide a reset output within a predictable range of the supply voltage. A common threshold range is between 5% and 10% below the nominal supply voltage. The 4.63V, 3.08V and 2.32V options of the LM3722/LM3723/LM3724 use highly accurate circuitry to ensure that the reset threshold occurs only within this range (for 5.0V, 3.3V and 2.5V supplies). Table 1 shows how the standard reset thresholds apply to 5.0V, 3.3V, and 2.5V nominal supply voltages. 8 resistor must be small enough so that the leakage current of all connected devices does not create an excessive voltage drop when the output is not activated. A resistor value of 100 kΩ will generally suffice. (Continued) TABLE 1. Monitored Tolerance Table Reset Threshold Supply Voltage 2.5V 3.3V 4.63 ± % 3.08 ± % 2.32 ± % 5.0V Negative-Going VCC Transients The LM3722/LM3723/LM3724 are relatively immune to short negative-going transients or glitches on VCC. Figure 2 shows the maximum pulse width a negative-going VCC transient can have without causing a reset pulse. In general, as the magnitude of the transient increases, going further below the threshold, the maximum allowable pulse width decreases. Typically, a VCC transient that goes 125 mV below the reset threshold and lasts 40 µs or less will not cause a reset pulse. A 0.1 µF bypass capacitor mounted as close as possible to the VCC pin will provide additional transient rejection. 90.8-94.4% 91.8-95.2% 90.8-94.8% Ensuring a Valid Reset Output Down to VCC = 0V When VCC falls below 1V, the LM3722 RESET output is unable to sink the rated current. A high-impedance CMOS logic input connected to RESET can therefore drift to undetermined voltages. To prevent this situation, a 100kΩ resistor should be connected from the RESET output to ground, as shown in Figure 1. A 100kΩ pull-up resistor to VCC is also recommended for the LM3723, if RESET is required to remain valid for VCC < 1V. 20014410 20014414 FIGURE 1. Circuit for RESET Valid from VCC = 0V FIGURE 2. Maximum Transient Duration without Causing a Reset Pulse vs. Reset Comparator Overdrive Open Drain Output (LM3724) An open drain output allows easy paralleling of multiple microprocessor reset circuits without requiring additional logic gates. Open drain outputs also allow interfacing devices of differing logic levels or families, since the output pull-up resistor may be connected to any supply voltage up to 5.5V, regardless of LM3724 VCC. The pull up resistor is calculated so that maximum current flow into RESET is less than 10 mA when activated. The Interfacing to µPs with Bidirectional Reset Pins Microprocessors with bidirectional reset pins, such as the Motorola 68HC11 series, can be connected to the LM3722 RESET output. To ensure a correct output on the LM3722 even when the microprocessor reset pin is in the opposite state, connect a 4.7kΩ resistor between the LM3722 RESET output and the µP reset pin, as shown in Figure 3. Buffer the LM3722 RESET output to other system components. 9 www.national.com LM3722/LM3723/LM3724 Applications Information LM3722/LM3723/LM3724 Typical Application Circuits 20014411 FIGURE 3. Interfacing to Microprocessors with Bidirectional Reset I/O 20014422 FIGURE 4. Regulator/Switch with Long-Term Overvoltage Lockout Prevents Overdissipation in Linear Regulator www.national.com 10 LM3722/LM3723/LM3724 Typical Application Circuits (Continued) 20014431 FIGURE 5. LM3722 Switch Debouncer 20014424 FIGURE 6. LM3723 Power-On Delay 11 www.national.com LM3722/LM3723/LM3724 5-Pin Microprocessor Reset Circuits Physical Dimensions inches (millimeters) unless otherwise noted 5-Lead SOT23-5 For Ordering, refer to Ordering Information table NS Package Number MF05A 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. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 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