LP4951CM

LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators August 2005 LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators General Description The LP4950C and LP4951C 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 LP4950C/LP4951C increases only slightly in dropout, prolonging battery life. The LP4950C in the popular 3-pin TO-92 package is pin compatible with older 5V regulators. The 8-lead LP4951C is available in a plastic surface mount package 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 output or programmed from 1.24V to 29V with an external pair of resistors. Careful design of the LP4950C/LP4951C 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 High accuracy 5V guaranteed 100mA 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 LP4951C 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 LP4950C LP4951C 20052825 20052801 © 2005 National Semiconductor Corporation DS200528 www.national.com LP4950C-5V and LP4951C Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Input Supply Voltage SHUTDOWN Input Voltage, Error Comparator Output Voltage, (Note 9) FEEDBACK Input Voltage (Note 9) (Note 10) Power Dissipation Junction Temperature (TJ) Ambient Storage Temperature Internally Limited +150˚C −65˚ to +150˚C −0.3 to +30V −0.3 to +30V Soldering Dwell Time, Temperature Wave Infrared Vapor Phase ESD 4 seconds, 260˚C 10 seconds, 240˚C 75 seconds, 219˚C TBD Operating Ratings (Note 1) −1.5 to +30V Maximum Input Supply Voltage Junction Temperature Range (Note 8) LP4950C, LP4951C −40˚C to 125˚C 30V Electrical Characteristics (Note 2) LP4950CZ Parameter Conditions (Note 2) LP4951CM Tested Typ 5.0 Limit (Note 3) Output Voltage TJ = 25˚C −25˚C ≤ TJ ≤ 85˚C Full Operating Temperature Range Output Voltage Output Voltage Temperature Coefficient Line Regulation (Note 14) Load Regulation (Note 14) Dropout Voltage (Note 5) 100 µA ≤ IL ≤ 100 mA TJ ≤ TJMAX (Note 12) 6V ≤ VIN ≤ 30V (Note 15) 100µA ≤ IL ≤ 100mA IL = 100µA IL = 100mA Ground Current IL = 100µA IL = 100mA Dropout Ground Current Current Limit Thermal Regulation Output Noise, 10 Hz to 100 kHz VIN = 4.5V IL = 100µA VOUT = 0 (Note 13) CL = 1µF CL = 200µF CL = 3.3µF (Bypass = 0.01µF Pins 7 to 1 (LP4951C) 160 0.05 430 160 100 200 220 0.2 0.04 0.1 50 380 75 8 110 0.2 0.4 0.2 0.3 80 150 450 600 150 170 15 19 200 230 5.1 4.9 5.15 4.85 5.2 4.8 5.24 4.76 150 Design Limit (Note 4) V max V min V max V min V max V min V max V min ppm/˚C % max % max % max % max mV max mV max mV max mV max µA max µA max mA max mA max µA max µA max mA max mA max %/W max µV rms µV rms µV rms Units www.national.com 2 LP4950C-5V and LP4951C Electrical Characteristics LP4951C Parameter Conditions (Note 2) Typ Tested Limit (Note 3) 1.285 1.295 1.185 1.165 Reference Voltage Feedback Pin Bias Current Reference Voltage Temperature Coefficient Feedback Pin Bias Current Temperature Coefficient Error Comparator Output Leakage Current Output Low Voltage Upper Threshold Voltage Lower Threshold Voltage Hysteresis Shutdown Input Input Logic Voltage Low (Regulator ON) High (Regulator OFF) Shutdown Pin Input Current VSHUTDOWN = 2.4V VSHUTDOWN = 30V Regulator Output Current in Shutdown (Note 11) 30 450 3 50 100 600 750 10 20 1.3 0.7 2.0 V V max V min µA max µA max µA max µA max µA max µA max VOH = 30V VIN = 4.5V IOL = 400µA (Note 4) (Note 6) (Note 6) 0.01 150 60 75 15 1 2 250 400 40 25 95 140 µA max µA max mV max mV max mV min mV min mV max mV max mV (Note 12) (Note 7) 20 50 0.1 40 60 1.335 1.135 Desgin Limit (Note 4) Units 8-PIN VERSIONS ONLY Reference Voltage 1.235 V max V max V min Vmin V max V min nA max nA max ppm/˚C nA/˚C 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 = 6V, IL = 100µA and CL = 1µF. 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 (VOUT = 5V), 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 = 6V. 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 95 mV 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, 160˚C/W for the molded plastic SOP (M). The above thermal resistances for the M package apply when the package is soldered directly to the PCB. 3 www.national.com LP4950C-5V and LP4951C Electrical Characteristics Note 9: May exceed input supply voltage. (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 50 mA 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 LP4951C is tested at 150˚C for IL = 1 mA. 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. Connection Diagrams TO-92 Plastic Package (Z) Surface-Mount Package (M) 20052802 Bottom View 20052826 Top View Ordering Information Package TO-92 (Z) M (M08A) Output Voltage 5.0V LP4950CZ-5.0 LP4951CM −40˚C < TJ < 125˚C −40˚C < TJ < 125˚C Temperature www.national.com 4 LP4950C-5V and LP4951C Typical Performance Characteristics Quiescent Current Dropout Characteristics 20052827 20052828 Input Current Input Current 20052829 20052830 Output Voltage vs. Temperature of 3 Representative Units Quiescent Current 20052831 20052832 5 www.national.com LP4950C-5V and LP4951C Typical Performance Characteristics Quiescent Current (Continued) Quiescent Current 20052833 20052834 Quiescent Current Short Circuit Current 20052835 20052836 Dropout Voltage Dropout Voltage 20052838 20052837 www.national.com 6 LP4950C-5V and LP4951C Typical Performance Characteristics LP4951C Minimum Operating Voltage (Continued) LP4951C Feedback Bias Current 20052839 20052840 LP4951C Feedback Pin Current LP4951C Error Comparator Output 20052841 20052842 LP4951C Comparator Sink Current Line Transient Response 20052843 20052844 7 www.national.com LP4950C-5V and LP4951C Typical Performance Characteristics Load Transient Response (Continued) Load Transient Response 20052845 20052846 LP4951C Enable Transient Output Impedance 20052848 20052847 Ripple Rejection Ripple Rejection 20052849 20052850 www.national.com 8 LP4950C-5V and LP4951C Typical Performance Characteristics Ripple Rejection (Continued) Output Noise 20052851 20052852 LP4951C Divider Resistance Shutdown Threshold Voltage 20052853 20052854 Line Regulation LP4951C Maximum Rated Output Current 20052855 20052857 9 www.national.com LP4950C-5V and LP4951C Typical Performance Characteristics (Continued) Thermal Response 20052858 Application Hints 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. 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 5 Ω or less and a resonant frequency above 500 kHz. The value of this capacitor may be increased without limit. At lower values of output current, less output capacitance is required for stability. The capacitor can be reduced to 0.33 µF for currents below 10 mA or 0.1 µF for currents below 1 mA. Using the 8-pin version 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 100 mA load at 1.23V output (Output shorted to Feedback) a 3.3 µF (or greater) capacitor should be used. Unlike many other regulators, the LP4950C 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 LP4951C version with external resistors, a minimum load of 1µA is recommended. A 0.1µF capacitor should be placed from the LP4950C/ LP4951C 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 LP4951C 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 fix this problem. ERROR DETECTION COMPARATOR OUTPUT The comparator produces a logic low output whenever the LP4951C output falls out of regulation by more than approximately 5%. This figure is the comparator’s built-in offset of about 60 mV 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 4951C. 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 below gives a timing diagram depicting the ERROR signal and the regulated output voltage as the LP4951C 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 which VOUT = 4.75V). Since the LP4951C’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. 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. www.national.com 10 LP4950C-5V and LP4951C Application Hints (Continued) 20052820 *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 (10 kΩ suggested), to ensure a low-level logic signal during any fault condition, while still allowing a valid high logic level during normal operation. 20052807 *See Application Hints FIGURE 1. ERROR Output Timing PROGRAMMING THE OUTPUT VOLTAGE (LP4951C) The LP4951C may be pin-strapped for 5V using its internal voltage divider by tying the pin 1 (output) to pin 2 (sense) pins together, and also tying the pin 7 (feedback) and pin 6 (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 **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 (LP4951C) 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 LP4950C 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 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 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 LP4951C typically draws 60µA at no load with Pin 2 opencircuited, this is a small price to pay. 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. 11 www.national.com LP4950C-5V and LP4951C www.national.com 20052823 Schematic Diagram 12 LP4950C-5V and LP4951C Physical Dimensions inches (millimeters) unless otherwise noted Surface Mount Package (M) NS Package Number M08A Molded TO-92 Package (Z) NS Package Number Z03A 13 www.national.com LP4950C-5V and LP4951C Adjustable Micropower Voltage Regulators Notes 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. 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