LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators General Description Features The LP2952 and LP2953 are micropower voltage regulators with very low quiescent current (130 µA typical at 1 mA load) and very low dropout voltage (typ. 60 mV at light load and 470 mV at 250 mA load current). They are ideally suited for battery-powered systems. Furthermore, the quiescent current increases only slightly at dropout, which prolongs battery life. n n n n n n n n n n The LP2952 and LP2953 retain all the desirable characteristics of the LP2951, but offer increased output current, additional features, and an improved shutdown function. The internal crowbar pulls the output down quickly when the shutdown is activated. The error flag goes low if the output voltage drops out of regulation. Reverse battery protection is provided. The internal voltage reference is made available for external use, providing a low-T.C. reference with very good line and load regulation. The parts are available in DIP and surface mount packages. Output voltage adjusts from 1.23V to 29V Guaranteed 250 mA output current Extremely low quiescent current Low dropout voltage Extremely tight line and load regulation Very low temperature coefficient Current and thermal limiting Reverse battery protection 50 mA (typical) output pulldown crowbar 5V and 3.3V versions available LP2953 Versions Only n Auxiliary comparator included with CMOS/TTL compatible output levels. Can be used for fault detection, low input line detection, etc. Applications n n n n High-efficiency linear regulator Regulator with under-voltage shutdown Low dropout battery-powered regulator Snap-ON/Snap-OFF regulator Block Diagrams LP2953 LP2952 01112702 01112701 © 2005 National Semiconductor Corporation DS011127 www.national.com LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators March 2005 LP2952/LP2952A/LP2953/LP2953A Pinout Drawings Ordering Information LP2952 14-Pin DIP LP2952 Temp. Range (TJ) ˚C Package NSC Drawing Number LP2952IN, LP2952AIN, LP2952IN-3.3, LP2952AIN-3.3 −40 to +125 14-Pin Molded DIP N14A LP2952IM, LP2952AIM, LP2952IM-3.3, LP2952AIM-3.3 −40 to +125 16-Pin Surface Mount M16A Temp. Range (TJ) ˚C Package NSC Drawing Number LP2953IN, LP2953AIN, LP2953IN-3.3, LP2953AIN-3.3 −40 to +125 16-Pin Molded DIP N16A LP2953IM, LP2953AIM, LP2953IM-3.3, LP2953AIM-3.3 −40 to +125 16-Pin Surface Mount M16A LP2953AMJ/883 5962-9233601MEA LP2953AMJ-QMLV 5962-9233601VEA −55 to +150 16-Pin Ceramic DIP LP2953AMWG/883 5962-9233601QXA LP2953AMWG-QMLV 5962-9233601VXA −55 to +150 16-Pin Ceramic Surface Mount Order Number 01112711 LP2953 16-Pin DIP LP2953 Order Number 01112713 LP2952 16-Pin SO 01112712 LP2953 16-Pin SO 01112714 www.national.com 2 J16A WG16A Maximum Junction Temperature LP2952I, LP2953I, LP2952AI, LP2953AI, LP2952I-3.3, LP2953I-3.3, LP2952AI-3.3, LP2953AI-3.3 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. −65˚C ≤ TA ≤ +150˚C Storage Temperature Range LP2953AM +150˚C Input Supply Voltage Operating Temperature Range LP2952I, LP2953I, LP2952AI, LP2953AI, LP2952I-3.3, LP2953I-3.3, LP2952AI-3.3, LP2953AI-3.3 −20V to +30V Feedback Input Voltage (Note 3) −40˚C ≤ TJ ≤ +125˚C −55˚C ≤ TA ≤ +125˚C LP2953AM Lead Temp. (Soldering, 5 seconds) Power Dissipation (Note 2) +125˚C −0.3V to +5V Comparator Input Voltage (Note 4) −0.3V to +30V Shutdown Input Voltage (Note 4) −0.3V to +30V Comparator Output Voltage (Note 4) −0.3V to +30V ESD Rating (Note 15) 2 kV 260˚C Internally Limited Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, bold typeface applies over the full operating temperature range. Limits are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CL = 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. 3.3V Versions Symbol VO Parameter Conditions Typical Output Voltage LP2952AI-3.3, LP2953AI-3.3 3.3 1 mA ≤ IL ≤ 250 mA 3.3 LP2952I-3.3, LP2953I-3.3 Min Max Min Max 3.284 3.317 3.267 3.333 3.260 3.340 3.234 3.366 3.254 3.346 3.221 3.379 Units V 5V Versions Symbol Parameter Conditions Typical LP2952AI, LP2953AI, LP2952I, LP2953I Units LP2953AM (Note 17) VO Output Voltage 5.0 1 mA ≤ IL ≤ 250 mA 5.0 Min Max Min Max 4.975 5.025 4.950 5.050 4.940 5.060 4.900 5.100 4.930 5.070 4.880 5.120 V All Voltage Options Electrical Characteristics Limits in standard typeface are for TJ = 25˚C, bold typeface applies over the full operating temperature range. Limits are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CL = 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. Symbol Parameter Conditions Typical LP2952AI, LP2953AI, LP2952I, LP2953I, LP2952AI-3.3, LP2952I-3.3, LP2953AI-3.3, LP2953I-3.3 LP2953AM (Notes 16, 17) Min Max Min Units Max REGULATOR Output Voltage Temp. Coefficient (Note 5) Output Voltage Line Regulation VIN = VO(NOM) + 1V to 30V 3 20 100 150 ppm/˚C 0.03 0.1 0.2 % 0.2 0.4 www.national.com LP2952/LP2952A/LP2953/LP2953A Absolute Maximum Ratings (Note 1) LP2952/LP2952A/LP2953/LP2953A All Voltage Options (Continued) Electrical Characteristics (Continued) Limits in standard typeface are for TJ = 25˚C, bold typeface applies over the full operating temperature range. Limits are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CL = 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. Symbol Parameter Conditions Typical LP2952AI, LP2953AI, LP2952I, LP2953I, LP2952AI-3.3, LP2952I-3.3, LP2953AI-3.3, LP2953I-3.3 LP2953AM (Notes 16, 17) Min Output Voltage Load Regulation (Note 6) VIN–VO Dropout Voltage (Note 7) IL = 1 mA to 250 mA 0.04 IL = 0.1 mA to 1 mA IL = 1 mA 60 IL = 50 mA 240 IL = 100 mA IGND Ground Pin Current (Note 8) 310 IL = 250 mA 470 IL = 1 mA 130 IL = 50 mA 1.1 IL = 100 mA 4.5 IL = 250 mA 21 100 150 150 300 300 420 420 400 400 520 520 600 600 800 800 170 170 200 200 2 2 2.5 2.5 6 6 8 8 28 28 mV µA mA 240 240 140 140 µA mA 105 ILIMIT Current Limit VOUT = 0 380 IL = 100 µA Thermal Regulation (Note 10) Output Noise Voltage (10 Hz to 100 kHz) IL = 100 mA CL = 4.7 µF 400 CL = 33 µF 260 CL = 33 µF (Note 11) Reference Voltage (Note 12) 0.05 500 500 530 530 0.2 0.2 µA %/W µV RMS 80 1.230 VIN = 2.5V to VO(NOM) + 1V 0.03 VIN = VO(NOM) + 1V to 30V (Note 13) Reference Voltage Load IREF = 0 to 200 µA Regulation www.national.com 100 33 VSHUTDOWN ≤ 1.1V Reference Voltage Temp. Coefficient 0.30 210 Ground Pin Current at Shutdown (Note 8) Reference Voltage Line Regulation 0.20 % 210 IGND VREF Max 0.20 165 Ground Pin Current at Dropout en Min 0.16 33 IGND VIN = VO(NOM) −0.5V Max Units 0.25 (Note 5) 20 4 1.215 1.245 1.205 1.255 1.205 1.255 1.190 1.270 0.1 0.2 0.2 0.4 0.4 0.8 0.6 1.0 V % % ppm/˚C (Continued) Electrical Characteristics (Continued) Limits in standard typeface are for TJ = 25˚C, bold typeface applies over the full operating temperature range. Limits are guaranteed by production testing or correlation techniques using standard Statistical Quality Control (SQC) methods. Unless otherwise specified: VIN = VO(NOM) + 1V, IL = 1 mA, CL = 2.2 µF for 5V parts and 4.7µF for 3.3V parts. Feedback pin is tied to V Tap pin, Output pin is tied to Output Sense pin. Symbol Parameter Conditions Typical LP2952AI, LP2953AI, LP2952I, LP2953I, LP2952AI-3.3, LP2952I-3.3, LP2953AI-3.3, LP2953I-3.3 LP2953AM (Notes 16, 17) Min IB(FB) Feedback Pin Bias Current IO(SINK) Output “OFF” Pulldown Current 20 (Note 9) Max Min Max 40 40 60 60 30 30 20 20 Units nA mA DROPOUT DETECTION COMPARATOR IOH Output “HIGH” Leakage VOH = 30V 0.01 1 2 2 VOL Output “LOW” Voltage VIN = VO(NOM) − 0.5V IO(COMP) = 400 µA 150 250 250 400 400 1 VTHR (MAX) Upper Threshold Voltage (Note 14) −60 −80 −95 −25 −95 −25 VTHR (MIN) Lower Threshold Voltage (Note 14) −85 −110 −55 −110 −55 −160 −40 −160 −40 HYST Hysteresis (Note 14) 15 (Referred to VREF) ±3 −35 −80 −35 µA mV mV mV mV SHUTDOWN INPUT (Note 15) VOS Input Offset HYST Hysteresis IB Input Bias Voltage −7.5 7.5 −7.5 7.5 −10 10 −10 10 −30 30 50 −30 50 nA −50 −30 −50 −30 30 −75 75 −7.5 7.5 10 −7.5 −10 7.5 10 mV −10 −7.5 7.5 −12 12 −30 30 50 30 50 nA −50 −30 −50 −30 30 −75 75 1 2 µA 250 400 mV 6 VIN(S/D) = 0V to 5V 10 Current LP2953AM 10 mV mV AUXILIARY COMPARATOR (LP2953 Only) VOS Input Offset Voltage ±3 (Referred to VREF) LP2953AM HYST Hysteresis IB Input Bias Current 6 VIN(COMP) = 0V to 5V 10 LP2953AM IOH ±3 Output “HIGH” Leakage VOH = 30V 10 mV 0.01 1 0.01 1 150 250 150 250 VIN(COMP) = 1.3V 2 LP2953AM 2.2 VOL Output “LOW” Voltage VIN(COMP) = 1.1V IO(COMP) = 400 µA 400 LP2953AM 420 5 www.national.com LP2952/LP2952A/LP2953/LP2953A All Voltage Options LP2952/LP2952A/LP2953/LP2953A All Voltage Options (Continued) Electrical Characteristics (Continued) Note 1: Absolute maximum ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of its rated operating conditions. Note 2: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, θJ–A, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature is calculated using the equation for P(MAX), . Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. See APPLICATION HINTS for additional information on heatsinking and thermal resistance. Note 3: When used in dual-supply systems where the regulator load is returned to a negative supply, the output voltage must be diode-clamped to ground. Note 4: May exceed the input supply voltage. Note 5: Output or reference voltage temperature coefficient is defined as the worst case voltage change divided by the total temperature range. Note 6: Load regulation is measured at constant junction temperature using low duty cycle pulse testing. Two separate tests are performed, one for the range of 100 µA to 1 mA and one for the 1 mA to 250 mA range. Changes in output voltage due to heating effects are covered by the thermal regulation specification. Note 7: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below the value measured with a 1V differential. At very low values of programmed output voltage, the input voltage minimum of 2V (2.3V over temperature) must be observed. Note 8: Ground pin current is the regulator quiescent current. The total current drawn from the source is the sum of the ground pin current, output load current, and current through the external resistive divider (if used). Note 9: VSHUTDOWN ≤ 1.1V, VOUT = VO(NOM). Note 10: Thermal regulation is the change in output voltage at a time T after a change in power dissipation, excluding load or line regulation effects. Specifications are for a 200 mA load pulse at VIN = VO(NOM)+15V (3W pulse) for T = 10 ms. Note 11: Connect a 0.1 µF capacitor from the output to the feedback pin. Note 12: VREF ≤ VOUT ≤ (VIN − 1V), 2.3V ≤ VIN ≤ 30V, 100 µA ≤ IL ≤ 250 mA. Note 13: Two separate tests are performed, one covering 2.5V ≤ VIN ≤ VO(NOM)+1V and the other test for VO(NOM)+1V ≤ VIN ≤ 30V. Note 14: Comparator thresholds are expressed in terms of a voltage differential at the Feedback terminal below the nominal reference voltage measured atVIN = VO(NOM) + 1V. To express these thresholds in terms of output voltage change, multiply by the Error amplifier gain, which is VOUT/VREF = (R1 + R2)/R2(refer to Figure 4). Note 15: Human body model, 200 pF discharged through 1.5 kΩ. Note 16: Drive Shutdown pin with TTL or CMOS-low level to shut regulator OFF, high level to turn regulator ON. Note 17: A military RETS specification is available upon request. For more information on military products, please refer to the Mil-Aero web page at http://www.national.com/appinfo/milaero/index.html. www.national.com 6 LP2952/LP2952A/LP2953/LP2953A Typical Performance Characteristics Unless otherwise specified: VIN = 6V, IL = 1 mA, CL = 2.2 µF, VSD = 3V, TA = 25˚C, VOUT = 5V. Quiescent Current Quiescent Current 01112727 01112728 Ground Pin Current vs Load Ground Pin Current 01112730 01112729 Ground Pin Current Output Noise Voltage 01112731 01112732 7 www.national.com LP2952/LP2952A/LP2953/LP2953A Typical Performance Characteristics Unless otherwise specified: VIN = 6V, IL = 1 mA, CL = 2.2 µF, VSD = 3V, TA = 25˚C, VOUT = 5V. (Continued) Ripple Rejection Ripple Rejection 01112733 01112734 Ripple Rejection Line Transient Response 01112736 01112735 Line Transient Response Output Impedance 01112737 01112738 www.national.com 8 Load Transient Response Load Transient Response 01112739 01112740 Dropout Characteristics Enable Transient 01112742 01112741 Short-Circuit Output Current and Maximum Output Current Enable Transient 01112743 01112744 9 www.national.com LP2952/LP2952A/LP2953/LP2953A Typical Performance Characteristics Unless otherwise specified: VIN = 6V, IL = 1 mA, CL = 2.2 µF, VSD = 3V, TA = 25˚C, VOUT = 5V. (Continued) LP2952/LP2952A/LP2953/LP2953A Typical Performance Characteristics Unless otherwise specified: VIN = 6V, IL = 1 mA, CL = 2.2 µF, VSD = 3V, TA = 25˚C, VOUT = 5V. (Continued) Feedback Bias Current Feedback Pin Current 01112745 01112746 Error Output Comparator Sink Current 01112748 01112747 Dropout Detection Comparator Threshold Voltages Divider Resistance 01112749 www.national.com 01112750 10 Thermal Regulation Minimum Operating Voltage 01112751 01112752 Dropout Voltage 01112753 11 www.national.com LP2952/LP2952A/LP2953/LP2953A Typical Performance Characteristics Unless otherwise specified: VIN = 6V, IL = 1 mA, CL = 2.2 µF, VSD = 3V, TA = 25˚C, VOUT = 5V. (Continued) LP2952/LP2952A/LP2953/LP2953A Schematic Diagram 01112706 the ground pins of the IC, and into the copper of the PC board. Details on heatsinking using PC board copper are covered later. To determine if a heatsink is required, the maximum power dissipated by the regulator, P(max), must be calculated. It is important to remember that if the regulator is powered from a transformer connected to the AC line, the maximum specified AC input voltage must be used (since this produces the maximum DC input voltage to the regulator). Figure 1 shows the voltages and currents which are present in the circuit. The formula for calculating the power dissipated in the regulator is also shown in Figure 1: Application Hints HEATSINK REQUIREMENTS (Industrial Temperature Range Devices) The maximum allowable power dissipation for the LP2952/ LP2953 is limited by the maximum junction temperature (+125˚C) and the external factors that determine how quickly heat flows away from the part: the ambient temperature and the junction-to-ambient thermal resistance for the specific application. The industrial temperature range (−40˚C ≤ TJ ≤ +125˚C) parts are manufactured in plastic DIP and surface mount packages which contain a copper lead frame that allows heat to be effectively conducted away from the die, through www.national.com 12 LP2952/LP2952A/LP2953/LP2953A Application Hints (Continued) 01112707 FIGURE 1. PTOTAL = (VIN − VOUT) IL + (VIN) IG Current/Voltage Diagram The next parameter which must be calculated is the maximum allowable temperature rise, TR(max). This is calculated by using the formula: TR(max) = TJ(max) − TA(max)θ(J–A) = TR(max)/P(max) where: TJ(max) is the maximum allowable junction temperature TA(max) is the maximum ambient temperature Using the calculated values for TR(max) and P(max), the required value for junction-to-ambient thermal resistance, θ(J–A), can now be found: The heatsink is made using the PC board copper. The heat is conducted from the die, through the lead frame (inside the part), and out the pins which are soldered to the PC board. The pins used for heat conduction are given in Table 1. 01112708 * For best results, use L = 2H ** 14-Pin DIP is similar, refer to Table 1 for pins designated for heatsinking. FIGURE 2. Copper Heatsink Patterns TABLE 1. Heat Conducting Pins Part LP2952IN, LP2952AIN, Package Pins 14-Pin DIP 3, 4, 5, LP2952IN-3.3, LP2952AIN-3.3 LP2953IN, LP2953AIN, TABLE 2. Thermal Resistance for Various Copper Heatsink Patterns 10, 11, 12 Package 16-Pin DIP 4, 5, 12, 13 16-Pin DIP LP2953IN-3.3, LP2953AIN-3.3 LP2952IM, LP2952AIM, LP2952IM-3.3, LP2952AIM-3.3, 16-Pin Surface Mount 1, 8, 9, 16 14-Pin DIP LP2953IM, LP2953AIM, LP2953IM-3.3, LP2953AIM-3.3 Surface Mount Figure 2 shows copper patterns which may be used to dissipate heat from the LP2952 and LP2953. Table 2 shows some values of junction-to-ambient thermal resistance (θJ–A) for values of L and W for 1 oz. copper. θJ–A (˚C/W) L (in.) H (in.) 1 0.5 70 2 1 60 3 1.5 58 4 0.19 66 6 0.19 66 1 0.5 65 2 1 51 3 1.5 49 1 0.5 83 2 1 70 3 1.5 67 6 0.19 69 4 0.19 71 2 0.19 73 HEATSINK REQUIREMENTS (Military Temperature Range Devices) The maximum allowable power dissipation for the LP2953AMJ is limited by the maximum junction temperature (+150˚C) and the two parameters that determine how quickly heat flows away from the die: the ambient temperature and the junction-to-ambient thermal resistance of the part. 13 www.national.com LP2952/LP2952A/LP2953/LP2953A Application Hints 100 pF capacitor between the Output and Feedback pins and increasing the output capacitance to 6.8 µF (or greater) will cure the problem. (Continued) The military temperature range (−55˚C ≤ TJ ≤+150˚C) parts are manufactured in ceramic DIP packages which contain a KOVAR lead frame (unlike the industrial parts, which have a copper lead frame). The KOVAR material is necessary to attain the hermetic seal required in military applications. The KOVAR lead frame does not conduct heat as well as copper, which means that the PC board copper can not be used to significantly reduce the overall junction-to-ambient thermal resistance in applications using the LP2953AMJ part. MINIMUM LOAD When setting the output voltage using an external resistive divider, a minimum current of 1 µA is recommended through the resistors to provide a minimum load. It should be noted that a minimum load current is specified in several of the electrical characteristic test conditions, so this value must be used to obtain correlation on these tested limits. The power dissipation calculations for military applications are done exactly the same as was detailed in the previous section, with one important exception: the value for θ(J–A), the junction-to-ambient thermal resistance, is fixed at 95˚C/W and can not be changed by adding copper foil patterns to the PC board. This leads to an important fact: The maximum allowable power dissipation in any application using the LP2953AMJ is dependent only on the ambient temperature: 01112726 Figure 3 shows a graph of maximum allowable power dissipation vs. ambient temperature for the LP2953AMJ, made using the 95˚C/W value for θ(J–A) and assuming a maximum junction temperature of 150˚C (caution: the maximum ambient temperature which will be reached in a given application must always be used to calculate maximum allowable power dissipation). FIGURE 3. Power Derating Curve for LP2953AMJ PROGRAMMING THE OUTPUT VOLTAGE The regulator may be pin-strapped for 5V operation using its internal resistive divider by tying the Output and Sense pins together and also tying the Feedback and 5V Tap pins together. Alternatively, it may be programmed for any voltage between the 1.23V reference and the 30V maximum rating using an external pair of resistors (see Figure 4). The complete equation for the output voltage is: EXTERNAL CAPACITORS A 2.2 µF (or greater) capacitor is required between the output pin and ground to assure stability when the output is set to 5V. Without this capacitor, the part will oscillate. Most type of tantalum or aluminum electrolytics will work here. Film types will work, but are more expensive. Many aluminum electrolytics contain electrolytes which freeze at −30˚C, which requires the use of solid tantalums below −25˚C. The important parameters of the capacitor are an ESR of about 5Ω or less and a resonant frequency above 500 kHz (the ESR may increase by a factor of 20 or 30 as the temperature is reduced from 25˚C to −30˚C). 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 0.68 µF for currents below 10 mA or 0.22 µF for currents below 1 mA. Programming the output for voltages below 5V runs the error amplifier at lower gains requiring more output capacitance for stability. At 3.3V output, a minimum of 4.7 µF is required. For the worst-case condition of 1.23V output and 250 mA of load current, a 6.8 µF (or larger) capacitor should be used. A 1 µF capacitor should be placed from the input pin to ground if there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery input is used. Stray capacitance to the Feedback terminal can cause instability. This problem is most likely to appear when using high value external resistors to set the output voltage. Adding a www.national.com where VREF is the 1.23V reference and IFB is the Feedback pin bias current (−20 nA typical). The minimum recommended load current of 1 µA sets an upper limit of 1.2 MΩ on the value of R2 in cases where the regulator must work with no load (see MINIMUM LOAD ). IFB will produce a typical 2% error in VOUT which can be eliminated at room temperature by trimming R1. For better accuracy, choosing R2 = 100 kΩ will reduce this error to 0.17% while increasing the resistor program current to 12 µA. Since the typical quiescent current is 120 µA, this added current is negligible. 14 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. (Continued) 01112710 01112709 * See Application Hints * In shutdown mode, ERROR will go high if it has been pulled up to an external supply. To avoid this invalid response, pull up to regulator output. ** Drive with TTL-low to shut down ** Exact value depends on dropout voltage. (See Application Hints) FIGURE 4. Adjustable Regulator FIGURE 5. ERROR Output Timing DROPOUT VOLTAGE The dropout voltage of the regulator is defined as the minimum input-to-output voltage differential required for the output voltage to stay within 100 mV of the output voltage measured with a 1V differential. The dropout voltage is independent of the programmed output voltage. OUTPUT ISOLATION The regulator output can be left connected to an active voltage source (such as a battery) with the regulator input power shut off, as long as the regulator ground pin is connected to ground. If the ground pin is left floating, damage to the regulator can occur if the output is pulled up by an external voltage source. DROPOUT DETECTION COMPARATOR This comparator produces a logic “LOW” whenever the output falls out of regulation by more than about 5%. This figure results from the comparator’s built-in offset of 60 mV divided by the 1.23V reference (refer to block diagrams on page 1). The 5% low trip level remains constant regardless of the programmed output voltage. An out-of-regulation condition can result from low input voltage, current limiting, or thermal limiting. Figure 5 gives a timing diagram showing the relationship between the output voltage, the ERROR output, and input voltage as the input voltage is ramped up and down to a regulator programmed for 5V output. The ERROR signal becomes low at about 1.3V input. It goes high at about 5V input, where the output equals 4.75V. Since the dropout voltage is load dependent, the input voltage trip points will vary with load current. The output voltage trip point does not vary. The comparator has an open-collector output which requires an external pull-up resistor. This resistor may be connected to the regulator output or some other supply voltage. Using the regulator output prevents an invalid “HIGH” on the comparator output which occurs if it is pulled up to an external voltage while the regulator input voltage is reduced below 1.3V. In selecting a value for the pull-up resistor, note that while the output can sink 400 µA, this current adds to battery drain. Suggested values range from 100 kΩ to 1 MΩ. This resistor is not required if the output is unused. When VIN ≤ 1.3V, the error flag pin becomes a high impedance, allowing the error flag voltage to rise to its pull-up voltage. Using VOUT as the pull-up voltage (rather than an external 5V source) will keep the error flag voltage below 1.2V (typical) in this condition. The user may wish to divide REDUCING OUTPUT NOISE In reference applications it may be advantageous to reduce the AC noise present on the output. One method is to reduce regulator bandwidth by increasing output capacitance. This is relatively inefficient, since large increases in capacitance are required to get significant improvement. Noise can be reduced more effectively by a bypass capacitor placed across R1 (refer to Figure 4). The formula for selecting the capacitor to be used is: This gives a value of about 0.1 µF. When this is used, the output capacitor must be 6.8 µF (or greater) to maintain stability. The 0.1 µF capacitor reduces the high frequency gain of the circuit to unity, lowering the output noise from 260 µV to 80 µV using a 10 Hz to 100 kHz bandwidth. Also, noise is no longer proportional to the output voltage, so improvements are more pronounced at high output voltages. AUXILIARY COMPARATOR (LP2953 only) The LP2953 contains an auxiliary comparator whose inverting input is connected to the 1.23V reference. The auxiliary comparator has an open-collector output whose electrical characteristics are similar to the dropout detection comparator. The non-inverting input and output are brought out for external connections. 15 www.national.com LP2952/LP2952A/LP2953/LP2953A Application Hints LP2952/LP2952A/LP2953/LP2953A Application Hints (Continued) 5V Current Limiter with Load Fault Indicator SHUTDOWN INPUT A logic-level signal will shut off the regulator output when a “LOW” ( < 1.2V) is applied to the Shutdown input. To prevent possible mis-operation, the Shutdown input must be actively terminated. If the input is driven from opencollector logic, a pull-up resistor (20 kΩ to 100 kΩ recommended) should be connected from the Shutdown input to the regulator input. If the Shutdown input is driven from a source that actively pulls high and low (like an op-amp), the pull-up resistor is not required, but may be used. If the shutdown function is not to be used, the cost of the pull-up resistor can be saved by simply tying the Shutdown input directly to the regulator input. IMPORTANT: Since the Absolute Maximum Ratings state that the Shutdown input can not go more than 0.3V below ground, the reverse-battery protection feature which protects the regulator input is sacrificed if the Shutdown input is tied directly to the regulator input. 01112716 * Output voltage equals +VIN minum dropout voltage, which varies with output current. Current limits at a maximum of 380 mA (typical). ** Select R1 so that the comparator input voltage is 1.23V at the output voltage which corresponds to the desired fault current value. If reverse-battery protection is required in an application, the pull-up resistor between the Shutdown input and the regulator input must be used. Low T.C. Current Sink Typical Applications Basic 5V Regulator 01112715 01112717 www.national.com 16 LP2952/LP2952A/LP2953/LP2953A Typical Applications (Continued) 5V Regulator with Error Flags for LOW BATTERY and OUT OF REGULATION 01112718 * Connect to Logic or µP control inputs. LOW BATT flag warns the user that the battery has discharged down to about 5.8V, giving the user time to recharge the battery or power down some hardware with high power requirements. The output is still in regulation at this time. OUT OF REGULATION flag indicates when the battery is almost completely discharged, and can be used to initiate a power-down sequence. 5V Battery Powered Supply with Backup and Low Battery Flag 01112719 The circuit switches to the NI-CAD backup battery when the main battery voltage drops below about 5.6V, and returns to the main battery when its voltage is recharged to about 6V. The 5V MAIN output powers circuitry which requires no backup, and the 5V MEMORY output powers critical circuitry which can not be allowed to lose power. * The BATTERY LOW flag goes low whenever the circuit switches to the NI-CAD backup battery. 17 www.national.com LP2952/LP2952A/LP2953/LP2953A Typical Applications (Continued) 5V Regulator with Error Flags for LOW BATTERY and OUT OF REGULATION with SNAP-ON/SNAP-OFF Output 5V Regulator with Timed Power-On Reset 01112723 * Connect to Logic or µP control inputs. 01112720 OUTPUT has SNAP-ON/SNAP-OFF feature. LOW BATT flag warns the user that the battery has discharged down to about 5.8V, giving the user time to recharge the battery or shut down hardware with high power requirements. The output is still in regulation at this time. Timing Diagram for Timed Power-On Reset OUT OF REGULATION flag goes low if the output goes below about 4.7V, which could occur from a load fault. OUTPUT has SNAP-ON/SNAP-OFF feature. Regulator snaps ON at about 5.7V input, and OFF at about 5.6V. 01112721 * RT = 1 MEG, CT = 0.1 µF 5V Regulator with Snap-On/Snap-Off Feature and Hysteresis 01112722 * Turns ON at VIN = 5.87V Turns OFF at VIN = 5.64V (for component values shown) www.national.com 18 LP2952/LP2952A/LP2953/LP2953A Typical Applications (Continued) 5V Regulator with Timed Power-On Reset, Snap-On/Snap-Off Feature and Hysteresis Timing Diagram 01112725 Td = (0.28) RC = 28 ms for components shown. 01112724 FIGURE 6. 19 www.national.com LP2952/LP2952A/LP2953/LP2953A Physical Dimensions inches (millimeters) unless otherwise noted 16-Pin Ceramic DIP Order Number LP2953AMJ/883, 5962-9233601MEA, LP2953AMJ-QMLV, 5962-9233601VEA NS Package Number J16A 16-Pin Surface Mount Order Number LP2952IM, LP2952AIM, LP2952IM-3.3, LP2952AIM-3.3, LP2953IM, LP2953AIM, LP2953IM-3.3 or LP2953AIM-3.3 NS Package Number M16A www.national.com 20 LP2952/LP2952A/LP2953/LP2953A Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 14-Pin Molded DIP Order Number LP2952IN, LP2952AIN, LP2952IN-3.3 or LP2952AIN-3.3 NS Package Number N14A 16-Pin Molded DIP Order Number LP2953IN, LP2953AIN, LP2953IN-3.3 or LP2953AIN-3.3 NS Package Number N16A 21 www.national.com LP2952/LP2952A/LP2953/LP2953A Adjustable Micropower Low-Dropout Voltage Regulators Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Pin Ceramic Surface-Mount Order Number LP2953AMWG/883, 5962-9233601QXA, LP2953AMWG-QMLV, 5962-9233601VXA NS Package Number WG16A 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. 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