LP2950

LP2950/2951 Micrel LP2950/2951 100mA Low-Dropout Voltage Regulator General Description The LP2950 and LP2951 are micropower voltage regulators with very low dropout voltage (typically 40mV at light loads and 380mV at 100mA), and very low quiescent current (75µA typical). The quiescent current of the LP2950/LP2951 increases only slightly in dropout, thus prolonging battery life. This feature, among others, makes the LP2950 and LP2951 ideally suited for use in battery-powered systems. Available in a 3-Pin TO-92 package, the LP2950 is pincompatible with the older 5V regulators. Additional system functions, such as programmable output voltage and logiccontrolled shutdown, are available in the 8-pin DIP and 8-pin SOIC versions of the LP2951. Features • • • • • • • • High accuracy 5V, guaranteed 100 mA output Extremely low quiescent current Low-dropout voltage Extremely tight load and line regulation Very low temperature coefficient Use as regulator or reference Needs only 1µF for stability Current and thermal limiting LP2951 Versions Only • • • Error flag warns of output dropout Logic-controlled electronic shutdown Output programmable from 1.24 to 29V Applications • • • Automotive Electronics Voltage Reference Avionics 3 Block Diagram and Pin Configurations UNREGULATED DC + 7 FEEDBACK 8 INPUT 1 OUTPUT 2 SENSE + 5V 150 mA MAX. 3 FROM CMOS OR TTL SHUTDOWN 60 mV + 1.23 V REF. + – ERROR AMPLIFIER 182 kΩ 60 kΩ 6 5V TAP 5 ERROR 4 GROUND + 1.5 µF 330 kΩ TO CMOS OR TTL + – ERROR DETECTION COMPARATOR LP2950 and LP2951 Block Diagram (Pin Numbers Refer to LP2951) 1 8 7 6 5 32 OUTPUT 1 INPUT OUTPUT SENSE SHUTDOWN GROUND INPUT FEEDBACK 5V TAP ERROR 2 3 4 GROUND TO-92 Plastic Package Bottom View (BZ) DIP and SO Packages (BN and BM) See MIC2950 for a part with 1) higher output (150 mA), 2) transient protection (60V), and 3) reverse input protection to –20V) February 1999 3-35 LP2950/2951 Additional features available with the LP2951 also include an error flag output that warns of a low output voltage, which is often due to failing batteries on the input. This may also be used as a power-on reset. A logic-compatible shutdown input is also available which enables the regulator to be switched on and off. This part may also be pin-strapped for a 5V output, or programmed from 1.24V to 29V with the use of two external resistors. The LP2950 is available as either an -02 or -03 version. The -02 and -03 versions are guaranteed for junction temperatures Micrel from –40°C to +125°C; the -02 version has a tighter output and reference voltage specification range over temperature. The LP2951 is available as an -02 or -03 version. The LP2950 and LP2951 have a tight initial tolerance (0.5% typical), a very low output voltage temperature coefficient which allows use as a low-power voltage reference, and extremely good load and line regulation (0.05% typical). This greatly reduces the error in the overall circuit, and is the result of careful design techniques and process control. Ordering Information Part Number LP2950-02BZ LP2950-03BZ LP2951-02BM LP2951-03BM LP2951-02BN LP2951-03BN LP2951-4.8BM Voltage 5.0V 5.0V 5.0V 5.0V 5.0V 5.0V 4.85V Temperature Range* –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C –40°C to +125°C Package 3-Pin TO-92 plastic 3-Pin TO-92 plastic 8-Pin SOIC 8-Pin SOIC 8-Pin Plastic DIP 8-Pin Plastic DIP 8-Pin SOIC Accuracy 0.5% 1.0% 0.5% 1.0% 0.5% 1.0% 1.0% * Junction temperatures Absolute Maximum Ratings If Military/Aerospace specified devices are required, contact your local Micrel representative/distributor for availability and specifications. Power dissipation Lead Temperature (Soldering, 5 seconds) Storage Temperature Range Operating Junction Temperature Range (Note 8) LP2950, LP2951 Input Supply Voltage Feedback Input Voltage (Notes 9 and 10) Shutdown Input Voltage (Note 9) Error Comparator Output Voltage (Note 9) ESD Rating is to be determined. Internally Limited 260°C –65°C to +150°C –40°C to +125°C –0.3V to +30V –1.5V to +30V –0.3V to +30V –0.3V to +30V 3-36 February 1999 LP2950/2951 Micrel TA = 25°C except as noted. Min 4.975 4.950 4.802 4.950 4.925 4.777 4.940 4.900 4.753 4.930 4.880 4.733 20 50 50 0.03 0.04 0.04 0.04 0.10 0.10 50 380 100 8 180 Typ 5.000 5.000 4.850 Max 5.025 5.050 4.899 5.050 5.075 4.872 5.060 5.100 4.947 5.070 5.120 4.967 100 150 150 0.10 0.20 0.20 0.40 0.20 0.40 0.10 0.20 0.20 0.30 0.20 0.30 80 150 450 600 150 200 12 14 250 310 Units V V V V V V V V V V V V ppm/°C ppm/°C ppm/°C % % % % % % % % % % % % mV mV mV mV µA µA mA mA µA µA Electrical Characteristics Note 1 Parameter Output Voltage TJ = 25°C Condition LP295x-02 (± 0.5%) LP295x-03 (± 1%) LP2951-4.8 (± 1%) LP295x-02 (± 0.5%) LP295x-03 (± 1%) LP2951-4.8 (± 1%) LP295x-02 (± 0.5%), –40°C to +125°C LP295x-03 (± 1%), –40°C to +125°C LP2951-4.8 (± 1%), –40°C to +125°C LP295x-02 (± 0.5%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max) LP295x-03 (± 1%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max) LP2951-4.8 (± 1%), 100µA ≤ IL ≤ 100mA, TJ ≤ TJ(max) LP295x-02 (± 0.5%), Note 12 LP295x-03 (± 1%), Note 12 LP2951-4.8 (± 1%), Note 12 LP295x-02 (± 0.5%), Notes 14, 15 LP295x-03 (± 1%), Notes 14, 15 LP2951-4.8 (± 1%), Notes 14, 15 Output Voltage –25°C ≤ TJ ≤ +85°C Output Voltage Over Full Temperature Range Output Voltage Over Load Variation Output Voltage Temperature Coefficient 3 Line Regulation Load Regulation LP295x-02 (± 0.5%), Note 14, 100µA ≤ IL ≤ 100mA LP295x-03 (± 1%), Note 14, 100µA ≤ IL ≤ 100mA LP2951-4.8 (± 1%), Note 14, 100µA ≤ IL ≤ 100mA Dropout Voltage Note 5, IL = 100µA Note 5, IL = 100mA Ground Current IL = 100µA IL = 100mA Dropout Current VIN = 4.5V, IL = 100µA February 1999 3-37 LP2950/2951 Parameter Current Limit Thermal Regulation Output Noise Condition VOUT = 0V Note 13 10Hz to 100kHz, CL = 1µF 10Hz to 100kHz, CL = 200µF 10Hz to 100kHz, CL = 3.3µF, 0.01µF bypass Feedback to Output Reference Voltage LP295x-02 (± 0.5%) LP295x-03 (± 1%) LP2951-4.8 (± 1%) Reference Voltage LP295x-02 (± 0.5%), Note 7 LP295x-03 (± 1%), Note 7 LP2951-4.8 (± 1%), Note 7 Feedback Bias Current Reference Voltage LP295x-02 (± 0.5%), Note 12 LP295x-03 (± 1%), Note 12 LP2951-4.8 (± 1%), Note 12 Feedback Bias Current Temperature Coefficient Output Leakage Current Output Low Voltage (Flag) Upper Threshold Voltage Lower Threshold Voltage Hysteresis Input Logic Voltage VOH = 30V VIN = 4.5V, IOL = 200µA Note 6 Note 6 Note 6 LP295x-02 (± 0.5%) Low High LP295x-03 (± 1%) Low High LP2951-4.8 (± 1%) Low High 40 25 1.220 1.200 1.210 1.200 1.210 1.200 1.190 1.185 1.185 20 20 50 50 0.1 0.01 150 60 75 15 1.3 0.7 2.0 1.3 0.7 2.0 1.3 0.7 2.0 95 140 1.00 2.00 250 400 Min Typ 160 0.05 430 160 100 1.235 1.235 1.235 1.250 1.260 1.260 1.270 1.260 1.270 1.270 1.285 1.285 40 60 Max 200 220 0.20 Micrel Units mA mA %/W µVRMS µVRMS µVRMS V V V V V V V V V nA nA ppm/°C ppm/°C ppm/°C nA/°C µA µA mV mV mV mV mV mV mV V V V V V V V V V 3-38 February 1999 LP2950/2951 Parameter Shutdown Input Current Condition VSHUTDOWN = 2.4V VSHUTDOWN = 30V Regulator Output Current in Shutdown Note 1: Note 2: Note 3: Note 4: Note 5: Micrel Min Typ 30 450 3 Max 50 100 600 750 10 20 Units µA µA µA µA µA µA Note 11 Boldface limits apply at temperature extremes. Unless otherwise specified all limits guaranteed for TJ = 25°C, VIN = 6V, IL = 100µA and CL = 1µF. Additional conditions for the 8-pin versions are Feedback tied to 5V Tap and Output tied to Output Sense (VOUT = 5V) and VSHUTDOWN ≤ 0.8V. Guaranteed and 100% production tested. Guaranteed but not 100% production tested. These limits are not used to calculate outgoing AQL levels. Dropout voltage is defined as the input to output differential at which the output voltage drops 100mV 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. Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured at 6V input. 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 = 384mV. 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. VREF ≤ VOUT ≤ (VIN – 1 V), 2.3V ≤ VIN ≤ 30V, 100µA < IL ≤ 100mA, TJ ≤ TJMAX. The junction-to-ambient thermal resistance of the TO-92 package is 180°C/W with 0.4” leads and 160°C/W with 0.25” leads to a PC board. The thermal resistance of the 8-pin DIP package is 105°C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the SOIC (M) package is 160°C/W. May exceed input supply voltage. Note 6: Note 7: Note 8: 3 Note 9: Note 10: When used in dual-supply systems where the output terminal sees loads returned to a negative supply, the output voltage should be diodeclamped to ground. Note 11: VSHUTDOWN ≥ 2V, VIN ≤ 30 V, VOUT = 0, with Feedback pin tied to 5V Tap. 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 in 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. February 1999 3-39 LP2950/2951 Micrel Typical Performance Characteristics 10 Quiescent Current 6 OUTPUT VOLTAGE (VOLTS) Dropout Characteristics INPUT CURRENT (µA) Input Current 250 225 200 175 150 125 100 75 50 25 0 GROUND PIN CURRENT (mA) 5 4 3 2 1 0 0 1 2 3 4 5 6 R L = 50 Ω R L = 50kΩ R L = 50k Ω 1 RL = ∞ 0.1 0.01 0.1 1 10 150 01234 5 6 7 8 9 10 LOAD CURRENT (mA) INPUT VOLTAGE (VOLTS) INPUT VOLTAGE (VOLTS) Input Current 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 Output Voltage vs. Temperature of 3 Representative Units 5.06 OUTPUT VOLTAGE (V) Ground Current 320 GROUND CURRENT (µA) INPUT CURRENT (mA) R L = 50 Ω 5.04 5.02 5.0 4.98 4.96 0.2% 280 240 200 160 120 80 40 0 0 1 2 3 4 5 6 7 8 INPUT VOLTAGE (VOLTS) IL = 1 mA IL = 0 01 234 5 67 8 9 10 4.94 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) INPUT VOLTAGE (VOLTS) Quiescent Current 240 QUIESCENT CURRENT (µA) GROUND CURRENT (mA) Ground Current 16 GROUND CURRENT (mA) Ground Current 16 14 12 10 8 6 4 2 0 0 1 2 3 4 5 6 7 8 INPUT VOLTAGE (V) IL = 100 mA 220 VIN = 6V IL = 100 µA 200 12 VIN = 6V IL = 100 mA 8 180 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) 4 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) Short Circuit Current SHORT CIRCUIT CURRENT (mA) Drop-out Voltage 600 DROP-OUT VOLTAGE (mV) Drop-out Voltage 500 DROP-OUT VOLTAGE (mV) 170 160 150 140 130 120 110 100 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) 500 400 300 100 50 IL = 100 mA 400 300 200 TJ = 25 °C 100 0 IL = 100 µA 0 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) 100 µA 1 mA 10 mA 100 mA OUTPUT CURRENT 3-40 February 1999 LP2950/2951 Micrel MINIMUM OPERATING VOLTAGE (V) 2.2 2.1 2.0 1.9 1.8 1.7 LP2951 Minimum Operating Voltage BIAS CURRENT (nA) 20 10 0 -10 -20 LP2951 Feedback Bias Current FEEDBACK CURRENT (µA) 50 0 -50 -100 -150 -200 LP2951 Feedback Pin Current PIN 7 DRIVEN BY EXTERNAL SOURCE (REGULATOR RUN OPEN LOOP) TA = 125°C TA = 25°C 1.6 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) -30 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) TA = –55°C -250 -2.0 -1.5 -1.0 -0.5 0 0.5 1.0 FEEDBACK VOLTAGE (V) 8 COMPARATOR OUTPUT (V) 2.5 SINK CURRENT (mA) VOUT = 5V 6 4 HYSTERESIS 2 0 -2 0 PULLUP RESISTOR TO SEPARATE 5V SUPPLY 2.0 1.5 1.0 0.5 TA = 125°C OUTPUT VOLTAGE CHANGE LP2951 Error Comparator Output LP2951 Comparator Sink Current 100 mV 50 mV 0 -50 mV 8V 6V 4V Line Transient Response TA = 25°C 1 2 3 4 5 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 OUTPUT LOW VOLTAGE (V) INPUT VOLTAGE TA = -55°C C L = 1 µF IL = 1 mA VOUT = 5V 3 0 200 400 600 800 INPUT VOLTAGE (V) TIME (µs) Load Transient Response OUTPUT VOLTAGE LOAD CHANGE (mV) CURRENT Load Transient Response SHUTDOWN OUTPUT PIN VOLTAGE (V) VOLTAGE (V) LP2951 Enable Transient 7 6 5 4 3 2 1 0 2 0 -2 L L = 1 µF 250 200 150 100 50 0 -50 -100 100 mA 100 µA 0 1 2 LOAD CURRENT C L = 1 µF VOUT = 5V 80 60 40 20 0 -20 -40 -60 100 mA 100 µA 0 4 8 OUTPUT VOLTAGE CHANGE (mV) C L = 10 µF VOUT = 5V IL = 10 mA VIN = 8V CL = 10 µF VOUT = 5V 3 4 5 12 16 20 -100 0 100 200 300 400 500 600 700 TIME (µs) TIME (ms) TIME (ms) Output Impedance OUTPUT IMPEDANCE (OHMS) Ripple Rejection 90 RIPPLE REJECTION (dB) Ripple Rejection 90 RIPPLE REJECTION (dB) 10 5 2 1 0.5 0.2 0.1 0.05 0.02 0.01 I0 = 100 µA I0 = 1 mA I0 = 100 mA VOUT = 5V C L = 1 µF 80 70 60 50 40 30 20 CL = 1 µF VIN = 6V VOUT = 5V 101 10 2 10 3 IL = 100 µA IL = 0 80 70 I = 1 mA L 60 50 40 30 20 101 CL = 1 µF VIN = 6V VOUT = 5V IL = 10 mA 102 10 3 10 4 10 5 106 FREQUENCY (Hz) 10 100 1K 10K 100K 1M 10 4 10 106 FREQUENCY (Hz) FREQUENCY (Hz) February 1999 3-41 LP2950/2951 Micrel Typical Performance Characteristics (Continued) 80 RIPPLE REJECTION (dB) 70 60 50 40 IL = 50 µA VOLTAGE NOISE SPECTRAL DENSITY (µV/√Hz) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 PIN 2 TO PIN 4 RESISTANCE (kΩ ) Ripple Rejection Output Noise IL = 100 mA CL = 1 µF CL = 220 µF CL = 3.3 µF 0.01 µF BYPASS PIN 1 TO PIN 7 LP2951 Divider Resistance 400 300 IL = 100 mA 200 CL = 1 µF 30 VIN = 6V VOUT = 5V 20 10 101 102 10 3 10 4 10 5 106 100 0.0 102 10 3 10 4 10 5 0 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) FREQUENCY (Hz) FREQUENCY (Hz) SHUTDOWN THRESHOLD VOLTAGE (V) 1.8 1.6 1.4 1.2 1.0 0.8 0.6 -75 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) OUTPUT VOLTAGE CHANGE (mV) Shutdown Threshold Voltage Line Regulation OUTPUT CURRENT (mA) LP2950 Maximum Rated Output Current 120 100 80 60 40 20 0 TA = 50°C TA = 85°C 8-PIN MOLDED DIP SOLDERED TO PC BOARD 30 25 20 15 T = 150°C 10 J 5 0 10 5 TJ = 125°C 0 -5 -10 5 10 15 IL = 100 µA IL = 1 mA T J MAX = 125°C VOUT = 5V TA = 25°C IL = 100 µA 20 25 30 0 INPUT VOLTAGE (V) 5 10 15 20 25 INPUT VOLTAGE (V) 30 POWER OUTPUT VOLTAGE DISSIPATION (W) CHANGE (mV) 120 OUTPUT CURRENT (mA) LP2950 Maximum Rated Output TO-92 PACKAGE 0.25" LEADS SOLDERED TO PC BOARD Thermal Response 5 4 2 0 -2 1 0 -1 0 10 20 30 40 50 TIME (µs) 1.25W 100 80 T J 60 40 20 0 0 5 10 15 TA = 85°C MAX = 125°C TA = 25°C 20 25 30 INPUT VOLTAGE (V) 3-42 February 1999 LP2950/2951 Micrel 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 (approximately 4.75V) does not vary with load. The error comparator has an open-collector output which requires an external pull-up resistor. Depending on system requirements, this resistor may be returned to the 5V output or some other supply voltage. 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 1MΩ. The resistor is not required if this output is unused. Applications Information External Capacitors A 1.0µF (or greater) capacitor is required between the LP2950/ LP2951 output and ground to prevent oscillations due to instability. Most types of tantalum or aluminum electrolytics will be adequate; film types will work, but are costly and therefore not recommended. Many aluminum electrolytics have electrolytes that freeze at about –30°C, so solid tantalum capacitors are recommended for operation below –25°C. The important parameters of the capacitor are an effective series resistance of about 5Ω or less and a resonant frequency above 500kHz. The value of this capacitor may be increased without limit. At lower values of output current, less output capacitance is required for output stability. The capacitor can be reduced to 0.33µF for current below 10mA or 0.1µF for currents below 1mA. Using the 8-Pin 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 3.3 µF (or greater) capacitor should be used. The LP2950 will remain stable and in regulation with no load in addition to the internal voltage divider, unlike many other voltage regulators. This is especially important in CMOS RAM keep-alive applications. When setting the output voltage of the LP2951 version with external resistors, a minimum load of 1µA is recommended. A 0.1µF 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 (pin 7) 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 remedy this. Programming the Output Voltage (LP2951) The LP2951 may be pin-strapped for 5V using its internal voltage divider by tying Pin 1 (output) to Pin 2 (SENSE) and Pin 7 (FEEDBACK) to Pin 6 (5V TAP). Alternatively, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating. An external pair of resistors is required, as shown in Figure 2. The complete equation for the output voltage is VOUT = VREF x { 1 + R1/R2 } + IFB R2 where VREF is the nominal 1.235 reference voltage and IFB is the feedback pin bias current, nominally 20 nA. The minimum recommended load current of 1 µA 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 = 100kΩ reduces this error to 0.17% while increasing the resistor program current to 12µA. Since the LP2951 typically draws 60 µA at no load with Pin 2 open-circuited, this is a small price to pay. 3 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 method by which noise can be reduced on the 3 lead LP2950 and 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 1 CBYPASS ≅ 2 π R1 • 200 Hz or about 0.01 µF. When doing this, the output capacitor must be increased to 3.3 µF 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. Error Detection Comparator Output A logic low output will be produced by the comparator 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 1.235V reference voltage. (Refer to the block diagram on Page 1). This trip level remains “5% below normal” regardless of the programmed output voltage of the LP2951. 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. Figure 1 is a timing diagram depicting the ERROR signal and the regulated output voltage as the LP2951 input is ramped up and down. The ERROR signal becomes valid (low) at about 1.3V input. It goes high at about 5V input (the input voltage at February 1999 3-43 LP2950/2951 +VIN 100kΩ ERROR OUTPUT 5 ERROR 8 VIN VOUT 1 Micrel *SEE APPLICATIONS INFORMATION 4.75V OUTPUT VOLTAGE ERROR NOT VALID * * NOT VALID VOUT = V REF R1 x (1 + ) R2 VOUT 1.2 30V LP2951 LP2951 SHUTDOWN 3 SD INPUT OFF 3.3µF GND 4 FB 7 R1 100 pF 1.23V R2 INPUT VOLTAGE 1.3V 5V ON NOTE: PINS 2 AND 6 ARE LEFT OPEN * SEE APPLICATIONS INFORMATION V REF Figure 1. ERROR Output Timing Figure 2. Adjustable Regulator Typical Applications +V IN +VIN 8 +VIN ERROR OUTPUT 5 ERROR *VOUT ≈VIN VOUT 1 ERROR OUTPUT *SLEEP INPUT 47kΩ 8 +V IN 5 ERROR V OUT 1 C-MOS GATE 870 23 470 kΩ +V OUT 200kΩ + 2N3906 1% 100kΩ 100pF LP2951 SHUTDOWN 3 SO INPUT GND 4 LP2951 MIC2951 FB 7 SHUTDOWN 3 SD INPUT OFF GND ON 4 FB 7 3.3µF 1% 100kΩ *MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV, DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160mA. *HIGH INPUT LOWERS VOUT TO 2.5V Wide Input Voltage Range Current Limiter 5 V Regulator with 2.5 V Sleep Function 3-44 February 1999 LP2950/2951 +V = 2 → 30V IL↓ LOAD I L= 1.23 R Micrel +V IN +V IN VOUT LP2950Z VOUT LP2951 1 *V OUT = 5V 8 VIN + 0.1µF 1µF SHUTDOWN 3 SD INPUT GND 4 GND FB 7 R 1% 1µF 5 Volt Current Limiter * MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 40mV TO 400mV, DEPENDING ON LOAD CURRENT. Low Drift Current Source +V IN 8 +V IN 2 SENSE D1 3 D2 MEMORY V+ 20 1µF 3.6V NICAD VOUT 1 LP2951 #1 5 ERROR GND 4 27kΩ 2.7MΩ Q1 D4 D3 EARLY WARNING RESET 8 +V IN 2 SENSE VOUT 1 330kΩ MAIN OUTPUT µP VDO 3 SD LP2951 #2 5 ERROR GND 4 + 1µf Regulator with Early Warning and Auxiliary Output • EARLY WARNING FLAG ON LOW INPUT VOLTAGE • MAIN OUTPUT LATCHES OFF AT LOWER INPUT VOLTAGES • BATTERY BACKUP ON AUXILIARY OUTPUT OPERATION: REG. #1’S VOUT IS PROGRAMMED ONE DIODE DROP ABOVE 5 V. ITS ERROR FLAG BECOMES ACTIVE WHEN VIN ≤ 5.7 V. WHEN VIN DROPS BELOW 5.3 V, THE ERROR FLAG OF REG. #2 BECOMES ACTIVE AND VIA Q1 LATCHES THE MAIN OUTPUT OFF. WHEN VIN AGAIN EXCEEDS 5.7 V REG. #1 IS BACK IN REGULATION AND THE EARLY WARNING SIGNAL RISES, UNLATCHING REG. #2 VIA D3. February 1999 3-45 LP2950/2951 +V IN 4 20mA 8 +5V 4.7mA 1 V OUT MIC2951 7 FB GND 4 1N457 4V 2 360 1 4 Micrel 8 470k 5 470k 3 RESET +V IN ERROR VOUT 1 VOUT R1 7 FB GND 4 R2 + 1µF 0.1µF 1N 4001 V IN OUTPUT* 5 LP2951 SD * HIGH FOR IL < 3.5mA MIN. VOLTAGE Latch Off When Error Flag Occurs Open Circuit Detector for 4mA to 20mA Current Loop 39kΩ 5 RESET 8 +VIN ERROR 2 SENSE VOUT 1 7 +VOUT = 5V + 1µF LP2951 – C4 + 3 39kΩ SD GND 4 TAP 6 FB + 6V 1% LEADACID BATTERY 1% C1-C4 LP339 100 kΩ 1 kΩ 1 kΩ 10kΩ 20kΩ – + – + C1 100kΩ