LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators General Description The LP2950 and LP2951 are micropower voltage regulators with very low quiescent current (75µA typ.) and very low dropout voltage (typ. 40mV at light loads and 380mV at 100mA). They are ideally suited for use in battery-powered systems. Furthermore, the quiescent current of the LP2950/ LP2951 increases only slightly in dropout, prolonging battery life. The LP2950-5.0 is available in the surface-mount D-Pak package, and in the popular 3-pin TO-92 package for pincompatibility with older 5V regulators. The 8-lead LP2951 is available in plastic, ceramic dual-in-line, LLP, or metal can packages and offers additional system functions. One such feature is an error flag output which warns of a low output voltage, often due to falling batteries on the input. It may be used for a power-on reset. A second feature is the logic-compatible shutdown input which enables the regulator to be switched on and off. Also, the part may be pin-strapped for a 5V, 3V, or 3.3V output (depending on the version), or programmed from 1.24V to 29V with an external pair of resistors. Careful design of the LP2950/LP2951 has minimized all contributions to the error budget. This includes a tight initial tolerance (.5% typ.), extremely good load and line regulation (.05% typ.) and a very low output voltage temperature coefficient, making the part useful as a low-power voltage reference. Features n n n n n n n n n n n 5V, 3V, and 3.3V versions available High accuracy output voltage Guaranteed 100mA output current Extremely low quiescent current Low dropout voltage Extremely tight load and line regulation Very low temperature coefficient Use as Regulator or Reference Needs minimum capacitance for stability Current and Thermal Limiting Stable with low-ESR output capacitors (10mΩ to 6Ω) LP2951 versions only n Error flag warns of output dropout n Logic-controlled electronic shutdown n Output programmable from 1.24 to 29V Block Diagram and Typical Applications LP2950 LP2951 00854625 00854601 © 2005 National Semiconductor Corporation DS008546 www.national.com LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators May 2005 LP2950/LP2951 Connection Diagrams TO-252 (D-Pak) TO-92 Plastic Package (Z) 00854602 Bottom View 00854670 Front View Dual-In-Line Packages (N, J) Surface-Mount Package (M, MM) 8-Lead LLP 00854626 Top View Metal Can Package (H) 00854671 Pin 4 is fused to center DAP Top View 00854619 Top View 10-Lead Ceramic Surface-Mount Package (WG) 00854664 Top View www.national.com 2 Package Temperature Range Part Number Package Marking Transport Media NSC Drawing TO-92 (Z) −40 < TJ < 125 LP2950ACZ-3.0 2950A CZ3.0 Bag Z03A LP2950CZ-3.0 2950 CZ3.0 Bag LP2950ACZ-3.3 2950A CZ3.3 Bag LP2950CZ-3.3 2950 CZ3.3 Bag LP2950ACZ-5.0 2950A CZ5.0 Bag LP2950CZ-5.0 2950 CZ5.0 Bag LP2950CDT-3.0 LP2950CDT-3.0 75 Units/Rail TO-252 (D-Pak) −40 < TJ < 125 LP2950CDTX-3.0 LP2950CDT-3.3 2.5k Units Tape and Reel LP2950CDT-3.3 LP2950CDTX-3.3 LP2950CDT-5.0 M (M08A) −40 < TJ < 125 −40 < TJ < 125 LP2950CDT-5.0 2.5k Units Tape and Reel LP2951ACN-3.0 40 Units/Rail LP2951CN-3.0 LP2951CN-3.0 40 Units/Rail LP2951ACN-3.3 LP2951ACN-3.3 40 Units/Rail LP2951CN-3.3 LP2951CN-3.3 40 Units/Rail LP2951ACN LP2951ACN 40 Units/Rail LP2951CN LP2951CN 40 Units/Rail LP2951ACM-3.0 2951ACM30* (where * is die rev letter) 2.5k Units Tape and Reel LP2951CM-3.0 95 Units/Rail 2951CM30* (where * is die rev letter) 2.5k Units Tape and Reel 2951ACM33* (where * is die rev letter) 2.5k Units Tape and Reel 2951CM33* (where * is die rev letter) 2.5k Units Tape and Reel 2951ACM* (where * is die rev letter) 2.5k Units Tape and Reel LP2951CMX 2951CM* (where * is die rev letter) 2.5k Units Tape and Reel LP2951ACMM-3.0 L0BA 1k Units Tape and Reel LP2951CMX-3.0 LP2951ACM-3.3 LP2951ACMX-3.3 LP2951CM-3.3 LP2951CMX-3.3 LP2951ACM LP2951ACMX LP2951CM −40 < TJ < 125 75 Units/Rail LP2951ACN-3.0 LP2951ACMX-3.0 MM (MUA08A) 75 Units/Rail 2.5k Units Tape and Reel LP2950CDTX-5.0 N (N-08E) TD03B LP2951ACMMX-3.0 N08E M08A 95 Units/Rail 95 Units/Rail 95 Units/Rail 95 Units/Rail 95 Units/Rail MUA08A 3.5k Units Tape and Reel LP2951CMM-3.0 L0BB LP2951CMMX-3.0 1k Units Tape and Reel 3.5k Units Tape and Reel LP2951ACMM-3.3 L0CA LP2951ACMMX-3.3 1k Units Tape and Reel 3.5k Units Tape and Reel LP2951CMM-3.3 L0CB LP2951CMMX-3.3 1k Units Tape and Reel 3.5k Units Tape and Reel LP2951ACMM L0DA LP2951ACMMX 1k Units Tape and Reel 3.5k Units Tape and Reel LP2951CMM L0DB LP2951CMMX 1k Units Tape and Reel 3.5k Units Tape and Reel J (J08A) −55 < TJ < 150 LP2951J/883 See MIL/AERO Datasheet 40 Units/Rail J08A H (H08C) −55 < TJ < 150 LP2951H/883 See MIL/AERO Datasheet Tray H08C WG (WG10A) −55 < TJ < 150 LP2951WG/883 See MIL/AERO Datasheet Tray WG10A 3 www.national.com LP2950/LP2951 Ordering Information LP2950/LP2951 Ordering Information Package 8-lead LLP Temperature Range −40 < TJ < 125 (Continued) Part Number Package Marking LP2951ACSD-3.0 51AC30 LP2951ACSDX-3.0 LP2951CSD-3.0 51AC30B 51AC33B 2951AC 1k Units Tape and Reel 1k Units Tape and Reel 1k Units Tape and Reel 4.5k Units Tape and Reel 2951ACB LP2951CSDX www.national.com 1k Units Tape and Reel 4.5k Units Tape and Reel LP2951ACSDX LP2951CSD SDC08A 4.5k Units Tape and Reel LP2951CSDX-3.3 LP2951ACSD 1k Units Tape and Reel 4.5k Units Tape and Reel 51AC33 LP2951ACSDX-3.3 LP2951CSD-3.3 NSC Drawing 4.5k Units Tape and Reel LP2951CSDX-3.0 LP2951ACSD-3.3 Transport Media 1k Units Tape and Reel 4.5k Units Tape and Reel 4 ESD Rating Human Body Model(Note 18) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Supply Voltage Operating Ratings (Note 1) −0.3 to +30V Maximum Input Supply Voltage SHUTDOWN Input Voltage, Error Comparator Output Voltage, (Note 9) 30V Junction Temperature Range (TJ) (Note 8) FEEDBACK Input Voltage −1.5 to +30V (Note 9) (Note 10) Power Dissipation Internally Limited Junction Temperature (TJ) LP2951 −55˚ to +150˚C LP2950AC-XX, LP2950C-XX, LP2951AC-XX, LP2951C-XX −40˚ to +125˚C +150˚C Ambient Storage Temperature Soldering Dwell Time, Temperature Wave Infrared Vapor Phase 2500V −65˚ to +150˚C 4 seconds, 260˚C 10 seconds, 240˚C 75 seconds, 219˚C Electrical Characteristics (Note 2) LP2951 Conditions (Note 2) Parameter Tested Typ Limit Typ (Notes 3, 16) LP2950AC-XX LP2950C-XX LP2951AC-XX LP2951C-XX Tested Design Limit Limit Typ (Note 3) (Note 4) Tested Design Limit Limit Units (Note 3) (Note 4) 3V Versions (Note 17) Output Voltage TJ = 25˚C 3.0 3.015 3.0 2.985 −25˚C ≤ TJ ≤ 85˚C 3.015 3.0 2.985 3.0 3.0 3.030 3.030 3.0 2.970 Full Operating 3.0 Temperature Range Output Voltage 100µA ≤ IL ≤ 100mA 3.036 3.0 3.036 2.964 3.0 TJ ≤ TJMAX 3.0 2.964 3.045 3.042 3.0 2.955 V max 2.970 3.0 2.958 V min 3.045 V max 2.955 V min 3.060 V max 2.940 V min 3.072 V max 2.928 V min 3.3V Versions (Note 17) Output Voltage TJ = 25˚C 3.3 3.317 3.3 3.284 −25˚C ≤ TJ ≤ 85˚C 3.317 3.3 3.284 3.3 3.3 3.333 3.333 V max 3.267 V min 3.3 3.350 3.267 Full Operating 3.3 Temperature Range Output Voltage 100µA ≤ IL ≤ 100mA 3.340 3.3 3.340 3.260 3.3 TJ ≤ TJMAX 3.3 3.260 3.350 3.346 3.3 3.251 3.3 3.254 V max 3.251 V min 3.366 V max 3.234 V min 3.379 V max 3.221 V min 5V Versions (Note 17) Output Voltage TJ = 25˚C 5.0 5.025 5.0 4.975 −25˚C ≤ TJ ≤ 85˚C 5.0 Full Operating 5.0 5.025 5.0 4.975 5.0 5.05 5.0 4.95 5.06 5.0 5 5.05 V max 4.95 5.06 5.0 V min 5.075 V max 4.925 V min 5.1 V max www.national.com LP2950/LP2951 Absolute Maximum Ratings (Note 1) LP2950/LP2951 Electrical Characteristics (Note 2) (Continued) LP2951 Parameter Conditions (Note 2) Tested Typ Limit Typ (Notes 3, 16) Temperature Range Output Voltage 100µA ≤ IL ≤ 100mA LP2950AC-XX LP2950C-XX LP2951AC-XX LP2951C-XX Tested Design Limit Limit (Note 3) (Note 4) 4.94 5.0 TJ ≤ TJMAX Typ Tested Design Limit Limit (Note 3) (Note 4) 4.94 5.075 5.075 5.0 4.925 Units 5.0 4.925 4.9 V min 5.12 V max 4.88 V min 150 ppm/˚C All Voltage Options Output Voltage Temperature Coefficient (Note 12) Line Regulation (Note 14) 20 120 20 (VONOM + 1)V ≤ Vin ≤ 30V (Note 15) 0.03 0.1 0.03 Load Regulation (Note 14) 100µA ≤ IL ≤ 100mA 0.04 Dropout Voltage (Note 5) IL = 100µA 0.1 0.04 0.1 150 50 450 600 380 75 120 75 Vin = (VONOM − 0.5)V 170 200 0.2 0.3 150 50 600 380 8 12 150 120 170 12 160 200 0.05 0.2 200 170 160 200 0.05 0.2 µA max mA max 14 110 mV max µA max 14 110 mV max mV max 600 140 8 % max mV max 450 75 % max % max 140 12 110 % max 80 120 14 Dropout 0.1 450 380 8 0.2 0.4 80 140 IL = 100mA 0.04 0.2 80 Current 50 0.2 0.3 50 IL = 100µA 0.1 0.5 IL = 100mA Ground 100 mA max µA max Ground Current IL = 100µA Current Limit Vout = 0 160 200 Thermal Regulation (Note 13) 0.05 Output Noise, CL = 1µF (5V Only) 430 430 430 µV rms 10 Hz to 100 kHz CL = 200µF 160 160 160 µV rms 100 100 100 µV rms 220 200 220 0.2 µA max mA max 220 mA max %/W max CL = 3.3µF (Bypass = 0.01µF Pins 7 to 1 (LP2951) 8-pin Versions Only LP2951 Reference 1.235 Voltage LP2951AC-XX 1.25 1.235 1.26 (Note 7) Voltage Feedback Pin 20 Bias Current Reference Voltage www.national.com 1.22 1.26 V max 1.27 V max 1.21 V min 1.2 1.2 1.2 V min 1.27 1.27 1.285 V max 1.19 1.19 1.185 40 20 60 (Note 12) LP2951C-XX 1.235 1.26 1.22 Reference 1.25 40 20 60 20 20 6 40 60 50 V min nA max nA max ppm/˚C (Continued) LP2951 Parameter Conditions (Note 2) Tested Typ Limit Typ (Notes 3, 16) LP2950AC-XX LP2950C-XX LP2951AC-XX LP2951C-XX Tested Design Limit Limit Typ (Note 3) (Note 4) Tested Design Limit Limit Units (Note 3) (Note 4) All Voltage Options Temperature Coefficient Feedback Pin Bias 0.1 0.1 0.1 nA/˚C Current Temperature Coefficient Error Comparator Output Leakage VOH = 30V 0.01 1 Output Low Vin = (VONOM − 0.5)V 150 250 Voltage IOL = 400µA Upper Threshold (Note 6) Current 150 250 60 75 40 60 40 150 250 95 75 µA max mV max 400 60 95 µA max 2 40 25 140 (Note 6) 1 400 25 (Note 6) 0.01 2 400 Voltage Hysteresis 1 2 Voltage Lower Threshold 0.01 mV min 25 75 mV min 95 140 mV max mV max 140 mV max 15 15 15 mV 1.3 1.3 1.3 V Shutdown Input Input Logic Low (Regulator ON) 0.6 0.7 0.7 V max Voltage High (Regulator OFF) 2.0 2.0 2.0 V min Shutdown Pin Input Current Vshutdown = 2.4V 100 µA max 30 50 30 50 100 Vshutdown = 30V 450 600 450 600 750 Regulator Output Current in Shutdown (Note 11) 3 30 50 100 450 600 750 10 3 20 10 µA max 750 3 20 µA max 10 µA max µA max 20 µA max Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics tables. Note 2: Unless otherwise specified all limits guaranteed for VIN = (VONOM + 1)V, IL = 100µA and CL = 1µF for 5V versions and 2.2µF for 3V and 3.3V versions. Limits appearing in boldface type apply over the entire junction temperature range for operation. Limits appearing in normal type apply for TA = TJ = 25˚C. Additional conditions for the 8-pin versions are FEEDBACK tied to VTAP, OUTPUT tied to SENSE, and VSHUTDOWN ≤ 0.8V. Note 3: Guaranteed and 100% production tested. Note 4: Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels. Note 5: Dropout Voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential. At very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account. Note 6: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at Vin = (VONOM + 1)V. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = Vout/Vref = (R1 + R2)/R2.For example, at a programmed output voltage of 5V, the Error output is guaranteed to go low when the output drops by 95mV x 5V/1.235V = 384 mV. Thresholds remain constant as a percent of Vout as Vout is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. Note 7: Vref ≤ Vout ≤ (Vin − 1V), 2.3V ≤ Vin ≤ 30V, 100µA ≤ IL ≤ 100mA, TJ ≤ TJMAX. Note 8: The junction-to-ambient thermal resistances are as follows: 180˚C/W and 160˚C/W for the TO-92 package with 0.40 inch and 0.25 inch leads to the printed circuit board (PCB) respectively, 105˚C/W for the molded plastic DIP (N), 130˚C/W for the ceramic DIP (J), 160˚C/W for the molded plastic SOP (M), 200˚C/W for the molded plastic MSOP (MM), and 160˚C/W for the metal can package (H). The above thermal resistances for the N, J, M, and MM packages apply when the package is soldered directly to the PCB. Junction-to-case thermal resistance for the H package is 20˚C/W. Junction-to-case thermal resistance for the TO-252 package is 5.4˚C/W. The value of θJA for the LLP package is typically 51˚C/W but is dependent on the PCB trace area, trace material, and the number of layers and thermal vias. For details of thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187. Note 9: May exceed input supply voltage. 7 www.national.com LP2950/LP2951 Electrical Characteristics (Note 2) LP2950/LP2951 Electrical Characteristics (Note 2) (Continued) Note 10: When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diode-clamped to ground. Note 11: Vshutdown ≥ 2V, Vin ≤ 30V, Vout = 0, Feedback pin tied to VTAP. Note 12: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range. Note 13: Thermal regulation is defined as the change in output voltage at a time T after a change in power dissipation is applied, excluding load or line regulation effects. Specifications are for a 50mA load pulse at VIN = 30V (1.25W pulse) for T = 10ms. Note 14: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation. Note 15: Line regulation for the LP2951 is tested at 150˚C for IL = 1mA. For IL = 100µA and TJ = 125˚C, line regulation is guaranteed by design to 0.2%. See Typical Performance Characteristics for line regulation versus temperature and load current. Note 16: A Military RETS specification is available on request. At time of printing, the LP2951 RETS specification complied with the boldface limits in this column. The LP2951H, WG, or J may also be procured as Standard Military Drawing Spec #5962-3870501MGA, MXA, or MPA. Note 17: All LP2950 devices have the nominal output voltage coded as the last two digits of the part number. In the LP2951 products, the 3.0V and 3.3V versions are designated by the last two digits, but the 5V version is denoted with no code at this location of the part number (refer to ordering information table). Note 18: Human Body Model 1.5kΩ in series with 100pF. www.national.com 8 LP2950/LP2951 Typical Performance Characteristics Quiescent Current Dropout Characteristics 00854628 00854627 Input Current Input Current 00854629 00854630 Output Voltage vs. Temperature of 3 Representative Units Quiescent Current 00854632 00854631 9 www.national.com LP2950/LP2951 Typical Performance Characteristics (Continued) Quiescent Current Quiescent Current 00854633 00854634 Quiescent Current Short Circuit Current 00854635 00854636 Dropout Voltage Dropout Voltage 00854638 00854637 www.national.com 10 LP2950/LP2951 Typical Performance Characteristics (Continued) LP2951 Minimum Operating Voltage LP2951 Feedback Bias Current 00854639 00854640 LP2951 Feedback Pin Current LP2951 Error Comparator Output 00854642 00854641 LP2951 Comparator Sink Current Line Transient Response 00854643 00854644 11 www.national.com LP2950/LP2951 Typical Performance Characteristics (Continued) Load Transient Response Load Transient Response 00854645 00854646 LP2951 Enable Transient Output Impedance 00854648 00854647 Ripple Rejection Ripple Rejection 00854649 www.national.com 00854650 12 LP2950/LP2951 Typical Performance Characteristics (Continued) Ripple Rejection LP2951 Output Noise 00854651 00854652 LP2951 Divider Resistance Shutdown Threshold Voltage 00854653 00854654 Line Regulation LP2951 Maximum Rated Output Current 00854656 00854655 13 www.national.com LP2950/LP2951 Typical Performance Characteristics (Continued) LP2950 Maximum Rated Output Current Thermal Response 00854657 00854658 Output Capacitor ESR Range 00854663 www.national.com 14 EXTERNAL CAPACITORS A 1.0µF (or greater) capacitor is required between the output and ground for stability at output voltages of 5V or more. At lower output voltages, more capacitance is required (2.2µF or more is recommended for 3V and 3.3V versions). Without this capacitor the part will oscillate. Most types of tantalum or aluminum electrolytics work fine here; even film types work but are not recommended for reasons of cost. Many aluminum electrolytics have electrolytes that freeze at about −30˚C, so solid tantalums are recommended for operation below −25˚C. The important parameters of the capacitor are an ESR of about 5Ω or less and a resonant frequency above 500kHz. The value of this capacitor may be increased without limit. The error comparator has an open-collector output which requires an external pullup resistor. This resistor may be returned to the output or some other supply voltage depending on system requirements. In determining a value for this resistor, note that while the output is rated to sink 400µA, this sink current adds to battery drain in a low battery condition. Suggested values range from 100k to 1 MΩ. The resistor is not required if this output is unused. Ceramic capacitors whose value is greater than 1000pF should not be connected directly from the LP2951 output to ground. Ceramic capacitors typically have ESR values in the range of 5 to 10mΩ, a value below the lower limit for stable operation (see curve Output Capacitor ESR Range). The reason for the lower ESR limit is that the loop compensation of the part relies on the ESR of the output capacitor to provide the zero that gives added phase lead. The ESR of ceramic capacitors is so low that this phase lead does not occur, significantly reducing phase margin. A ceramic output capacitor can be used if a series resistance is added (recommended value of resistance about 0.1Ω to 2Ω). At lower values of output current, less output capacitance is required for stability. The capacitor can be reduced to 0.33µF for currents below 10mA or 0.1µF for currents below 1mA. Using the adjustable versions at voltages below 5V runs the error amplifier at lower gains so that more output capacitance is needed. For the worst-case situation of a 100mA load at 1.23V output (Output shorted to Feedback) a 3.3µF (or greater) capacitor should be used. Unlike many other regulators, the LP2950 will remain stable and in regulation with no load in addition to the internal voltage divider. This is especially important in CMOS RAM keep-alive applications. When setting the output voltage of the LP2951 versions with external resistors, a minimum load of 1µA is recommended. 00854620 *When VIN ≤ 1.3V, the error flag pin becomes a high impedance, and the error flag voltage rises to its pull-up voltage. Using VOUT as the pull-up voltage (see Figure 2), rather than an external 5V source, will keep the error flag voltage under 1.2V (typ.) in this condition. The user may wish to divide down the error flag voltage using equal-value resistors (10kΩ suggested), to ensure a low-level logic signal during any fault condition, while still allowing a valid high logic level during normal operation. FIGURE 1. ERROR Output Timing PROGRAMMING THE OUTPUT VOLTAGE (LP2951) The LP2951 may be pin-strapped for the nominal fixed output voltage using its internal voltage divider by tying the output and sense pins together, and also tying the feedback and VTAP pins together. Alternatively, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating. As seen in Figure 2, an external pair of resistors is required. The complete equation for the output voltage is A 1µF tantalum, ceramic or aluminum electrolytic capacitor should be placed from the LP2950/LP2951 input to ground if there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery is used as the input. Stray capacitance to the LP2951 Feedback terminal can cause instability. This may especially be a problem when using high value external resistors to set the output voltage. Adding a 100pF capacitor between Output and Feedback and increasing the output capacitor to at least 3.3µF will fix this problem. ERROR DETECTION COMPARATOR OUTPUT The comparator produces a logic low output whenever the LP2951 output falls out of regulation by more than approximately 5%. This figure is the comparator’s built-in offset of about 60mV divided by the 1.235 reference voltage. (Refer to the block diagram in the front of the datasheet.) This trip level remains “5% below normal” regardless of the programmed output voltage of the 2951. For example, the error flag trip level is typically 4.75V for a 5V output or 11.4V for a 12V output. The out of regulation condition may be due either to low input voltage, current limiting, or thermal limiting. where VREF is the nominal 1.235 reference voltage and IFB is the feedback pin bias current, nominally −20nA. The minimum recommended load current of 1µA forces an upper limit of 1.2 MΩ on the value of R2, if the regulator must work with no load (a condition often found in CMOS in standby). IFB will produce a 2% typical error in VOUT which may be eliminated at room temperature by trimming R1. For better accuracy, choosing R2 = 100k reduces this error to 0.17% while increasing the resistor program current to 12µA. Since the LP2951 typically draws 60µA at no load with Pin 2 opencircuited, this is a small price to pay. 15 www.national.com LP2950/LP2951 Figure 1 below gives a timing diagram depicting the ERROR signal and the regulated output voltage as the LP2951 input is ramped up and down. For 5V versions, the ERROR signal becomes valid (low) at about 1.3V input. It goes high at about 5V input (the input voltage at which VOUT = 4.75V). Since the LP2951’s dropout voltage is load-dependent (see curve in typical performance characteristics), the input voltage trip point (about 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load. Application Hints LP2950/LP2951 Application Hints (Continued) REDUCING OUTPUT NOISE In reference applications it may be advantageous to reduce the AC noise present at the output. One method is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way noise can be reduced on the 3 lead LP2950 but is relatively inefficient, as increasing the capacitor from 1µF to 220µF only decreases the noise from 430µV to 160µV rms for a 100kHz bandwidth at 5V output. Noise can be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick or about 0.01µF. When doing this, the output capacitor must be increased to 3.3µF to maintain stability. These changes reduce the output noise from 430µV to 100µV rms for a 100kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages. 00854607 *See Application Hints **Drive with TTL-high to shut down. Ground or leave open if shutdown feature is not to be used. Note: Pins 2 and 6 are left open. FIGURE 2. Adjustable Regulator Typical Applications 1A Regulator with 1.2V Dropout 00854622 300mA Regulator with 0.75V Dropout Wide Input Voltage Range Current Limiter 00854621 00854609 *Minimum input-output voltage ranges from 40mV to 400mV, depending on load current. Current limit is typically 160mA. www.national.com 16 LP2950/LP2951 Typical Applications (Continued) Low Drift Current Source 5 Volt Current Limiter 00854610 *Minimum input-output voltage ranges from 40mV to 400mV, depending on load current. Current limit is typically 160mA. 00854608 Regulator with Early Warning and Auxiliary Output Latch Off When Error Flag Occurs 00854612 00854611 j Early warning flag on low input voltage j Main output latches off at lower input voltages j Battery backup on auxiliary output j Operation: Reg. #1’s Vout is programmed one diode drop above 5V. Its error flag becomes active when Vin ≤ 5.7V. When Vin drops below 5.3V, the error flag of Reg. #2 becomes active and via Q1 latches the main output off. When Vin again exceeds 5.7V Reg. #1 is back in regulation and the early warning signal rises, unlatching Reg. #2 via D3. 17 www.national.com LP2950/LP2951 Typical Applications (Continued) 2 Ampere Low Dropout Regulator 00854613 For 5Vout, use internal resistors. Wire pin 6 to 7, & wire pin 2 to +Vout Bus. Open Circuit Detector for 4 → 20mA Current Loop 5V Regulator with 2.5V Sleep Function 00854615 00854614 *High input lowers Vout to 2.5V www.national.com 18 LP2950/LP2951 Typical Applications (Continued) Regulator with State-of-Charge Indicator 00854616 *Optional Latch off when drop out occurs. Adjust R3 for C2 Switching when Vin is 6.0V. **Outputs go low when Vin drops below designated thresholds. Low Battery Disconnect 00854617 For values shown, Regulator shuts down when Vin < 5.5V and turns on again at 6.0V. Current drain in disconnected mode is ≈ 150µA. *Sets disconnect Voltage **Sets disconnect Hysteresis 19 www.national.com LP2950/LP2951 Typical Applications (Continued) System Overtemperature Protection Circuit 00854618 LM34 for 125˚F Shutdown LM35 for 125˚C Shutdown www.national.com 20 www.national.com Schematic Diagram 00854623 LP2950/LP2951 21 LP2950/LP2951 Physical Dimensions inches (millimeters) unless otherwise noted Order Number LP2951WG/883 NS Package Number WG10A Metal Can Package (H) NS Package Number H08C www.national.com 22 LP2950/LP2951 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Ceramic Dual-In-Line Package (J) NS Package Number J08A Surface Mount Package (M) NS Package Number M08A 23 www.national.com LP2950/LP2951 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Molded Dual-In-Line Package (N) NS Package Number N08E Molded TO-92 Package (Z) NS Package Number Z03A www.national.com 24 LP2950/LP2951 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) Surface Mount Package (MM) NS Package Number MUA08A D-Pak Package NS Package Number TD03B 25 www.national.com LP2950/LP2951 Series of Adjustable Micropower Voltage Regulators Physical Dimensions inches (millimeters) unless otherwise noted (Continued) LLP Package NS Package Number SDC08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. 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