LM2671 SIMPLE SWITCHER® Power Converter High Efficiency 500mA Step-Down Voltage Regulator with Features General Description The LM2671 series of regulators are monolithic integrated circuits built with a LMDMOS process. These regulators provide all the active functions for a step-down (buck) switching regulator, capable of driving a 500mA load current with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5.0V, 12V, and an adjustable output version. Requiring a minimum number of external components, these regulators are simple to use and include patented internal frequency compensation (Patent Nos. 5,382,918 and 5,514,947), fixed frequency oscillator, external shutdown, soft-start, and frequency synchronization. The LM2671 series operates at a switching frequency of 260 kHz, thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Because of its very high efficiency (>90%), the copper traces on the printed circuit board are the only heat sinking needed. A family of standard inductors for use with the LM2671 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in the datasheet are selector guides for diodes and capacitors designed to work in switch-mode power supplies. Other features include a guaranteed ±1.5% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring typically 50 μA stand-by current. The output switch includes current limiting, as well as thermal shutdown for full protection under fault conditions. To simplify the LM2671 buck regulator design procedure, there exists computer design software, LM267X Made Simple (version 6.0). Features ■ Efficiency up to 96% ■ Available in SO-8, 8-pin DIP and LLP packages ■ Computer Design Software LM267X Made Simple (version 6.0) Simple and easy to design with Requires only 5 external components Uses readily available standard inductors 3.3V, 5.0V, 12V, and adjustable output versions Adjustable version output voltage range: 1.21V to 37V ±1.5% max output voltage tolerance over line and load conditions ■ Guaranteed 500mA output load current ■ 0.25Ω DMOS Output Switch ■ Wide input voltage range: 8V to 40V ■ 260 kHz fixed frequency internal oscillator ■ TTL shutdown capability, low power standby mode ■ Soft-start and frequency synchronization ■ Thermal shutdown and current limit protection ■ ■ ■ ■ ■ ■ Applications ■ Simple High Efficiency (>90%) Step-Down (Buck) Regulator ■ Efficient Pre-Regulator for Linear Regulators Typical Application (Fixed Output Voltage Versions) 10004201 SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation Windows® is a registered trademark of Microsoft Corporation. © 2007 National Semiconductor Corporation 100042 www.national.com LM2671 SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator with Features April 2007 LM2671 Connection Diagrams 16-Lead LLP Surface Mount Package Top View 8-Lead Package Top View 10004202 SO-8/DIP Package See NSC Package Drawing Number MO8A/N08E 10004241 LLP Package See NSC Package Drawing Number LDA16A TABLE 1. Package Marking and Ordering Information Output Voltage Order Information Package Marking Supplied as: 12 LM2671LD-12 S0005B 1000 Units on Tape and Reel 12 LM2671LDX-12 S0005B 4500 Units on Tape and Reel 3.3 LM2671LD-3.3 S0006B 1000 Units on Tape and Reel 3.3 LM2671LDX-3.3 S0006B 4500 Units on Tape and Reel 5.0 LM2671LD-5.0 S0007B 1000 Units on Tape and Reel 5.0 LM2671LDX-5.0 S0007B 4500 Units on Tape and Reel ADJ LM2671LD-ADJ S0008B 1000 Units on Tape and Reel ADJ LM2671LDX-ADJ S0008B 4500 Units on Tape and Reel 12 LM2671M-12 2671M-12 Shipped in Anti-Static Rails 12 LM2671MX-12 2671M-12 2500 Units on Tape and Reel 3.3 LM2671M-3.3 2671M-3.3 Shipped in Anti-Static Rails 3.3 LM2671MX-3.3 2671M-3.3 2500 Units on Tape and Reel 5.0 LM2671M-5.0 2671M-5.0 Shipped in Anti-Static Rails 5.0 LM2671MX-5.0 2671M-5.0 2500 Units on Tape and Reel ADJ LM2671M-ADJ 2671M-ADJ Shipped in Anti-Static Rails ADJ LM2671MX-ADJ 2671M-ADJ 2500 Units on Tape and Reel 12 LM2671N-12 LM2671N-12 Shipped in Anti-Static Rails 3.3 LM2671N-3.3 LM2671N-3.3 Shipped in Anti-Static Rails 5.0 LM2671N-5.0 LM2671N-5.0 Shipped in Anti-Static Rails ADJ LM2671N-ADJ LM2671N-ADJ Shipped in Anti-Static Rail 16 Lead LLP SO-8 DIP www.national.com 2 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature Range −65°C to +150°C Supply Voltage 45V Lead Temperature ON/OFF Pin Voltage −0.1V ≤ VSH ≤ 6V M Package Switch Voltage to Ground −1V Vapor Phase (60s) +215°C Boost Pin Voltage VSW + 8V Infrared (15s) +220°C Feedback Pin Voltage −0.3V ≤ VFB ≤ 14V N Package (Soldering, 10s) +260°C ESD Susceptibility LLP Package (See AN-1187) Human Body Model (Note 2) 2 kV Maximum Junction Temperature +150°C Power Dissipation Internally Limited Operating Ratings Supply Voltage Temperature Range 6.5V to 40V −40°C ≤ TJ ≤ +125°C Electrical Characteristics LM2671-3.3 Specifications with standard type face are for TJ = 25°C, and those in bold type face apply over full Operating Temperature Range. Symbol Parameter Conditions Typical (Note 4) Min (Note 5) Max (Note 5) Units V SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 3.3 3.251/3.201 3.350/3.399 VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 3.3 3.251/3.201 3.350/3.399 η Efficiency VIN = 12V, ILOAD = 500 mA 86 V % LM2671-5.0 Symbol Parameter Conditions Typical (Note 4) Min (Note 5) Max (Note 5) Units V SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT Output Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA 5.0 4.925/4.850 5.075/5.150 VOUT Output Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA 5.0 4.925/4.850 5.075/5.150 η Efficiency VIN = 12V, ILOAD = 500 mA 90 V % LM2671-12 Symbol Parameter Conditions Typical (Note 4) Min (Note 5) Max (Note 5) 11.82/11.64 12.18/12.36 Units SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT Output Voltage VIN = 15V to 40V, ILOAD = 20 mA to 500 mA 12 η Efficiency VIN = 24V, ILOAD = 500 mA 94 V % LM2671-ADJ Symbol Parameter Conditions Typ (Note 4) Min (Note 5) Max (Note 5) Units 1.210 1.192/1.174 1.228/1.246 V SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3) VFB Feedback Voltage VIN = 8V to 40V, ILOAD = 20 mA to 500 mA VOUT Programmed for 5V (see Circuit of Figure 3) 3 www.national.com LM2671 Absolute Maximum Ratings (Note 1) LM2671 Symbol VFB Parameter Conditions Typ (Note 4) Min (Note 5) Max (Note 5) Units 1.210 1.192/1.174 1.228/1.246 V Feedback Voltage VIN = 6.5V to 40V, ILOAD = 20 mA to 250 mA VOUT Programmed for 5V (see Circuit of Figure 3) η Efficiency VIN = 12V, ILOAD = 500 mA 90 % All Output Voltage Versions Specifications with standard type face are for TJ = 25°C, and those in bold type face apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V for the 3.3V, 5V, and Adjustable versions and VIN = 24V for the 12V version, and ILOAD = 100 mA. Symbol Parameters Conditions Typ Min Max Units 3.6 mA DEVICE PARAMETERS IQ Quiescent Current VFEEDBACK = 8V 2.5 For 3.3V, 5.0V, and ADJ Versions VFEEDBACK = 15V 2.5 mA For 12V Versions ISTBY Standby Quiescent Current ICL Current Limit IL Output Leakage Current ON/OFF Pin = 0V 100/150 μA 1.2/1.25 A 1 25 μA 6 15 mA 50 0.8 VIN = 40V, ON/OFF Pin = 0V 0.62/0.575 VSWITCH = 0V VSWITCH = −1V, ON/OFF Pin = 0V 0.40/0.60 Ω 275 kHz RDS(ON) Switch On-Resistance ISWITCH = 500 mA 0.25 fO Oscillator Frequency Measured at Switch Pin 260 D Maximum Duty Cycle 95 % Minimum Duty Cycle 0 % 85 nA IBIAS VS/D Feedback Bias VFEEDBACK = 1.3V Current ADJ Version Only ON/OFF Pin 225 1.4 0.8 2.0 7 37 V Voltage Thesholds μA IS/D ON/OFF Pin Current ON/OFF Pin = 0V 20 FSYNC Synchronization Frequency VSYNC = 3.5V, 50% duty cycle 400 kHz VSYNC Synchronization Threshold Voltage 1.4 V VSS Soft-Start Voltage 0.63 0.53 0.73 ISS Soft-Start Current 4.5 1.5 6.9 θJA Thermal Resistance N Package, Junction to Ambient (Note 6) 95 M Package, Junction to Ambient (Note 6) 105 V μA °C/W Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but device parameter specifications may not be guaranteed under these conditions. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. Note 3: External components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator performance. When the LM2671 is used as shown in Figure 2 and Figure 3 test circuits, system performance will be as specified by the system parameters section of the Electrical Characteristics. Note 4: Typical numbers are at 25°C and represent the most likely norm. Note 5: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. All limits are used to calculate Average Outgoing Quality Level (AOQL). Note 6: Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads. Additional copper area will lower thermal resistance further. See Application Information section in the application note accompanying this datasheet and the thermal model in LM267X Made Simple version 6.0 software. The value θJ−A for the LLP (LD) package is specifically dependent on PCB trace area, trace material, and the number of layers and thermal vias. For improved thermal resistance and power dissipation for the LLP package, refer to Application Note AN-1187. www.national.com 4 LM2671 Typical Performance Characteristics Normalized Output Voltage Line Regulation 10004204 10004203 Efficiency Drain-to-Source Resistance 10004205 10004206 Switch Current Limit Operating Quiescent Current 10004207 10004208 5 www.national.com LM2671 Standby Quiescent Current ON/OFF Threshold Voltage 10004209 10004210 ON/OFF Pin Current (Sourcing) Switching Frequency 10004212 10004211 Feedback Pin Bias Current Peak Switch Current 10004213 www.national.com 10004214 6 LM2671 Dropout Voltage—3.3V Option Dropout Voltage—5.0V Option 10004215 10004216 Block Diagram 10004217 * Patent Number 5,514,947 † Patent Number 5,382,918 FIGURE 1. 7 www.national.com LM2671 Typical Performance Characteristics (Circuit of Figure 2) Continuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 500 mA L = 100 μH, COUT = 100 μF, COUTESR = 0.1Ω Discontinuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 300 mA L = 15 μH, COUT = 68 μF (2×), COUTESR = 25 mΩ 10004218 A: VSW Pin Voltage, 10 V/div. B: Inductor Current, 0.2 A/div C: Output Ripple Voltage, 50 mV/div AC-Coupled 10004219 A: VSW Pin Voltage, 10 V/div. B: Inductor Current, 0.5 A/div C: Output Ripple Voltage, 20 mV/div AC-Coupled Horizontal Time Base: 1 μs/div Horizontal Time Base: 1 μs/div Load Transient Response for Continuous Mode VIN = 20V, VOUT = 5V L = 100 μH, COUT = 100 μF, COUTESR = 0.1Ω Load Transient Response for Discontinuous Mode VIN = 20V, VOUT = 5V, L = 47 μH, COUT = 68 μF, COUTESR = 50 mΩ 10004220 A: Output Voltage, 100 mV/div, AC-Coupled B: Load Current: 100 mA to 500 mA Load Pulse 10004221 A: Output Voltage, 100 mV/div, AC-Coupled B: Load Current: 100 mA to 400 mA Load Pulse Horizontal Time Base: 50 μs/div www.national.com Horizontal Time Base: 200 μs/div 8 LM2671 Test Circuit and Layout Guidelines 10004222 CIN - 22 μF, 50V Tantalum, Sprague “199D Series” COUT - 47 μF, 25V Tantalum, Sprague “595D Series” D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F L1 - 68 μH Sumida #RCR110D-680L CB - 0.01 μF, 50V Ceramic FIGURE 2. Standard Test Circuits and Layout Guides Fixed Output Voltage Versions 10004223 CIN - 22 μF, 50V Tantalum, Sprague “199D Series” COUT - 47 μF, 25V Tantalum, Sprague “595D Series” D1 - 3.3A, 50V Schottky Rectifier, IR 30WQ05F L1 - 68 μH Sumida #RCR110D-680L R1 - 1.5 kΩ, 1% CB - 0.01 μF, 50V Ceramic For a 5V output, select R2 to be 4.75 kΩ, 1% where VREF = 1.21V Use a 1% resistor for best stability. FIGURE 3. Standard Test Circuits and Layout Guides Adjustable Output Voltage Versions 9 www.national.com LM2671 LM2671 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) To simplify the buck regulator design procedure, National Semiconductor is making available computer design software to be used with the SIMPLE SWITCHER line of switching regulators. LM267X Made Simple (version 6.0) is available on Windows® 3.1, NT, or 95 operating systems. Given: Given: VOUT = Regulated Output Voltage (3.3V, 5V, or 12V) VOUT = 5V VIN(max) = Maximum DC Input Voltage VIN(max) = 12V ILOAD(max) = Maximum Load Current ILOAD(max) = 500 mA 1. Inductor Selection (L1) A. Select the correct inductor value selection guide from Figure 4 and Figure 5 or Figure 6 (output voltages of 3.3V, 5V, or 12V respectively). For all other voltages, see the design procedure for the adjustable version. B. From the inductor value selection guide, identify the inductance region intersected by the Maximum Input Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code (LXX). C. Select an appropriate inductor from the four manufacturer's part numbers listed in Figure 8. Each manufacturer makes a different style of inductor to allow flexibility in meeting various design requirements. Listed below are some of the differentiating characteristics of each manufacturer's inductors: Schott: ferrite EP core inductors; these have very low leakage magnetic fields to reduce electro-magnetic interference (EMI) and are the lowest power loss inductors Renco: ferrite stick core inductors; benefits are typically lowest cost inductors and can withstand E•T and transient peak currents above rated value. Be aware that these inductors have an external magnetic field which may generate more EMI than other types of inductors. Pulse: powered iron toroid core inductors; these can also be low cost and can withstand larger than normal E•T and transient peak currents. Toroid inductors have low EMI. Coilcraft: ferrite drum core inductors; these are the smallest physical size inductors, available only as SMT components. Be aware that these inductors also generate EMI—but less than stick inductors. Complete specifications for these inductors are available from the respective manufacturers. A table listing the manufacturers' phone numbers is located in Figure 9. 2. Output Capacitor Selection (COUT) A. Select an output capacitor from the output capacitor table in Figure 10. Using the output voltage and the inductance value found in the inductor selection guide, step 1, locate the appropriate capacitor value and voltage rating. www.national.com 1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown in Figure 5. B. From the inductor value selection guide shown in Figure 5, the inductance region intersected by the 12V horizontal line and the 500 mA vertical line is 47 μH, and the inductor code is L13. C. The inductance value required is 47 μH. From the table in Figure 8, go to the L13 line and choose an inductor part number from any of the four manufacturers shown. (In most instances, both through hole and surface mount inductors are available.) 2. Output Capacitor Selection (COUT) A. Use the 5.0V section in the output capacitor table in Figure 10. Choose a capacitor value and voltage rating from the line that contains the inductance value of 47 μH. The capacitance and voltage rating values corresponding to the 47 μH inductor are the: 10 EXAMPLE (Fixed Output Voltage Version) The capacitor list contains through-hole electrolytic capacitors from four different capacitor manufacturers and surface mount tantalum capacitors from two different capacitor manufacturers. It is recommended that both the manufacturers and the manufacturer's series that are listed in the table be used. A table listing the manufacturers' phone numbers is located in Figure 11. Surface Mount: 68 μF/10V Sprague 594D Series. 100 μF/10V AVX TPS Series. Through Hole: 68 μF/10V Sanyo OS-CON SA Series. 150 μF/35V Sanyo MV-GX Series. 150 μF/35V Nichicon PL Series. 150 μF/35V Panasonic HFQ Series. 3. Catch Diode Selection (D1) 3. Catch Diode Selection (D1) A. In normal operation, the average current of the catch diode is A. Refer to the table shown in Figure 12. In this example, a 1A, the load current times the catch diode duty cycle, 1-D (D is the 20V Schottky diode will provide the best performance. If the circuit switch duty cycle, which is approximately the output voltage divided must withstand a continuous shorted output, a higher current by the input voltage). The largest value of the catch diode average Schottky diode is recommended. current occurs at the maximum load current and maximum input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its maximum average current. However, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output condition. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency. This Schottky diode must be located close to the LM2671 using short leads and short printed circuit traces. 4. Input Capacitor (CIN) 4. Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is needed The important parameters for the input capacitor are the input between the input pin and ground to prevent large voltage voltage rating and the RMS current rating. With a maximum input transients from appearing at the input. This capacitor should be voltage of 12V, an aluminum electrolytic capacitor with a voltage located close to the IC using short leads. In addition, the RMS rating greater than 15V (1.25 × VIN) would be needed. The next current rating of the input capacitor should be selected to be at least higher capacitor voltage rating is 16V. ½ the DC load current. The capacitor manufacturer data sheet must The RMS current rating requirement for the input capacitor in a be checked to assure that this current rating is not exceeded. The buck regulator is approximately ½ the DC load current. In this curves shown in Figure 14 show typical RMS current ratings for example, with a 500 mA load, a capacitor with a RMS current rating several different aluminum electrolytic capacitor values. A parallel of at least 250 mA is needed. The curves shown in Figure 14 can connection of two or more capacitors may be required to increase be used to select an appropriate input capacitor. From the curves, the total minimum RMS current rating to suit the application locate the 16V line and note which capacitor values have RMS requirements. current ratings greater than 250 mA. For an aluminum electrolytic capacitor, the voltage rating should be For a through hole design, a 100 μF/16V electrolytic capacitor at least 1.25 times the maximum input voltage. Caution must be (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or exercised if solid tantalum capacitors are used. The tantalum equivalent) would be adequate. Other types or other capacitor voltage rating should be twice the maximum input manufacturers' capacitors can be used provided the RMS ripple voltage. The tables in Figure 15 show the recommended current ratings are adequate. Additionally, for a complete surface application voltage for AVX TPS and Sprague 594D tantalum mount design, electrolytic capacitors such as the Sanyo CV-C or capacitors. It is also recommended that they be surge current CV-BS and the Nichicon WF or UR and the NIC Components NACZ tested by the manufacturer. The TPS series available from AVX, series could be considered. and the 593D and 594D series from Sprague are all surge current For surface mount designs, solid tantalum capacitors can be used, tested. Another approach to minimize the surge current stresses but caution must be exercised with regard to the capacitor surge on the input capacitor is to add a small inductor in series with the current rating and voltage rating. In this example, checking Figure input supply line. 15, and the Sprague 594D series datasheet, a Sprague 594D 15 Use caution when using ceramic capacitors for input bypassing, μF, 25V capacitor is adequate. because it may cause severe ringing at the VIN pin. 11 www.national.com LM2671 PROCEDURE (Fixed Output Voltage Version) LM2671 PROCEDURE (Fixed Output Voltage Version) 5. Boost Capacitor (CB) This capacitor develops the necessary voltage to turn the switch gate on fully. All applications should use a 0.01 μF, 50V ceramic capacitor. 6. Soft-Start Capacitor (CSS - optional) This capacitor controls the rate at which the device starts up. The formula for the soft-start capacitor CSS is: EXAMPLE (Fixed Output Voltage Version) 5. Boost Capacitor (CB) For this application, and all applications, use a 0.01 μF, 50V ceramic capacitor. 6. Soft-Start Capacitor (CSS - optional) For this application, selecting a start-up time of 10 ms and using the formula for CSS results in a value of: where: ISS = Soft-Start Current :4.5 μA typical. tSS = Soft-Start Time :Selected. VSSTH = Soft-Start Threshold Voltage :0.63V typical. VOUT = Output Voltage :Selected. VSCHOTTKY = Schottky Diode Voltage Drop :0.4V typical. VIN = Input Voltage :Selected. If this feature is not desired, leave this pin open. With certain softstart capacitor values and operating conditions, the LM2671 can exhibit an overshoot on the output voltage during turn on. Especially when starting up into no load or low load, the softstart function may not be effective in preventing a larger voltage overshoot on the output. With larger loads or lower input voltages during startup this effect is minimized. In particular, avoid using softstart capacitors between 0.033µF and 1µF. 7. Frequency Synchronization (optional) 7. Frequency Synchronization (optional) The LM2671 (oscillator) can be synchronized to run with an For all applications, use a 1 kΩ resistor and a 100 pF capacitor for external oscillator, using the sync pin (pin 3). By doing so, the the RC filter. LM2671 can be operated at higher frequencies than the standard frequency of 260 kHz. This allows for a reduction in the size of the inductor and output capacitor. As shown in the drawing below, a signal applied to a RC filter at the sync pin causes the device to synchronize to the frequency of that signal. For a signal with a peak-to-peak amplitude of 3V or greater, a 1 kΩ resistor and a 100 pF capacitor are suitable values. www.national.com 12 LM2671 INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) 10004231 FIGURE 6. LM2671-12 10004229 FIGURE 4. LM2671-3.3 10004232 FIGURE 7. LM2671-ADJ 10004230 FIGURE 5. LM2671-5.0 Ind. Inducta nce Ref. Desg. (μH) Current (A) Schott Through Hole Surface Mount Renco Through Hole Pulse Engineering Surface Mount Through Hole Surface Mount Coilcraft Surface Mount L2 150 0.21 67143920 67144290 RL-5470-4 RL1500-150 PE-53802 PE-53802-S DO1608-154 L3 100 0.26 67143930 67144300 RL-5470-5 RL1500-100 PE-53803 PE-53803-S DO1608-104 L4 68 0.32 67143940 67144310 RL-1284-68-43 RL1500-68 PE-53804 PE-53804-S DO1608-683 L5 47 0.37 67148310 67148420 RL-1284-47-43 RL1500-47 PE-53805 PE-53805-S DO1608-473 L6 33 0.44 67148320 67148430 RL-1284-33-43 RL1500-33 PE-53806 PE-53806-S DO1608-333 L7 22 0.52 67148330 67148440 RL-1284-22-43 RL1500-22 PE-53807 PE-53807-S DO1608-223 L9 220 0.32 67143960 67144330 RL-5470-3 RL1500-220 PE-53809 PE-53809-S DO3308-224 L10 150 0.39 67143970 67144340 RL-5470-4 RL1500-150 PE-53810 PE-53810-S DO3308-154 L11 100 0.48 67143980 67144350 RL-5470-5 RL1500-100 PE-53811 PE-53811-S DO3308-104 L12 68 0.58 67143990 67144360 RL-5470-6 RL1500-68 PE-53812 PE-53812-S DO3308-683 L13 47 0.70 67144000 67144380 RL-5470-7 RL1500-47 PE-53813 PE-53813-S DO3308-473 L14 33 0.83 67148340 67148450 RL-1284-33-43 RL1500-33 PE-53814 PE-53814-S DO3308-333 L15 22 0.99 67148350 67148460 RL-1284-22-43 RL1500-22 PE-53815 PE-53815-S DO3308-223 L18 220 0.55 67144040 67144420 RL-5471-2 RL1500-220 PE-53818 PE-53818-S DO3316-224 L19 150 0.66 67144050 67144430 RL-5471-3 RL1500-150 PE-53819 PE-53819-S DO3316-154 L20 100 0.82 67144060 67144440 RL-5471-4 RL1500-100 PE-53820 PE-53820-S DO3316-104 L21 68 0.99 67144070 67144450 RL-5471-5 RL1500-68 13 PE-53821 PE-53821-S DO3316-683 www.national.com LM2671 FIGURE 8. Inductor Manufacturers' Part Numbers Coilcraft Inc. Coilcraft Inc., Europe Pulse Engineering Inc. Phone (800) 322-2645 FAX (708) 639-1469 Phone +44 1236 730 595 FAX +44 1236 730 627 Phone (619) 674-8100 FAX (619) 674-8262 Pulse Engineering Inc., Phone +353 93 24 107 Europe FAX +353 93 24 459 Renco Electronics Inc. Phone (800) 645-5828 FAX (516) 586-5562 Phone (612) 475-1173 FAX (612) 475-1786 Schott Corp. FIGURE 9. Inductor Manufacturers' Phone Numbers Output Capacitor Output Voltage (V) 3.3 5.0 12 Inductance (μH) Surface Mount Sprague 594D Series Through Hole AVX TPS Series Sanyo OS-CON SA Series Sanyo MV-GX Series Panasonic HFQ Series (μF/V) (μF/V) (μF/V) (μF/V) (μF/V) (μF/V) 22 120/6.3 100/10 100/10 330/35 330/35 330/35 33 120/6.3 100/10 68/10 220/35 220/35 220/35 47 68/10 100/10 68/10 150/35 150/35 150/35 68 120/6.3 100/10 100/10 120/35 120/35 120/35 100 120/6.3 100/10 100/10 120/35 120/35 120/35 150 120/6.3 100/10 100/10 120/35 120/35 120/35 22 100/16 100/10 100/10 330/35 330/35 330/35 33 68/10 10010 68/10 220/35 220/35 220/35 47 68/10 100/10 68/10 150/35 150/35 150/35 68 100/16 100/10 100/10 120/35 120/35 120/35 100 100/16 100/10 100/10 120/35 120/35 120/35 150 100/16 100/10 100/10 120/35 120/35 120/35 22 120/20 (2×) 68/20 68/20 330/35 330/35 330/35 33 68/25 68/20 68/20 220/35 220/35 220/35 47 47/20 68/20 47/20 150/35 150/35 150/35 68 47/20 68/20 47/20 120/35 120/35 120/35 100 47/20 68/20 47/20 120/35 120/35 120/35 150 47/20 68/20 47/20 120/35 120/35 120/35 220 47/20 68/20 47/20 120/35 120/35 120/35 FIGURE 10. Output Capacitor Table Nichicon Corp. Panasonic AVX Corp. www.national.com Nichicon PL Series Phone (847) 843-7500 FAX (847) 843-2798 Phone (714) 373-7857 FAX (714) 373-7102 Phone (845) 448-9411 14 Sanyo Corp. (845) 448-1943 Phone (207) 324-4140 FAX (207) 324-7223 Phone (619) 661-6322 FAX (619) 661-1055 LM2671 Sprague/Vishay FAX FIGURE 11. Capacitor Manufacturers' Phone Numbers 1A Diodes 3A Diodes VR Surface Mount Through Hole Surface Mount Through Hole 20V SK12 1N5817 SK32 1N5820 B120 SR102 SK13 1N5818 SK33 1N5821 30WQ03F 31DQ03 SK34 1N5822 30V 40V SR302 B130 11DQ03 MBRS130 SR103 SK14 1N5819 B140 11DQ04 30BQ040 MBR340 MBRS140 SR104 30WQ04F 31DQ04 10BQ040 MBRS340 SR304 10MQ040 MBRD340 15MQ040 50V SK15 MBR150 SK35 MBR350 B150 11DQ05 30WQ05F 31DQ05 10BQ050 SR105 SR305 FIGURE 12. Schottky Diode Selection Table International Rectifier Corp. Motorola, Inc. General Instruments Corp. Diodes, Inc. Phone (310) 322-3331 FAX (310) 322-3332 Phone (800) 521-6274 FAX (602) 244-6609 Phone (516) 847-3000 FAX (516) 847-3236 Phone (805) 446-4800 FAX (805) 446-4850 FIGURE 13. Diode Manufacturers' Phone Numbers 15 www.national.com LM2671 10004233 FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical) AVX TPS Recommended Application Voltage Recommended Application Voltage Voltage Rating Voltage Rating +85°C Rating +85°C Rating 5 10 3.3 6.3 8 16 5 10 12 20 10 20 18 25 12 25 24 35 15 35 29 50 Sprague 594D Recommended Application Voltage Voltage Rating +85°C Rating 2.5 3.3 4 6.3 FIGURE 15. Recommended Application Voltage for AVX TPS and Sprague 594D Tantalum Chip Capacitors Derated for 85°C. LM2671 Series Buck Regulator Design Procedure (Adjustable Output) PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) To simplify the buck regulator design procedure, National Semiconductor is making available computer design software to be used with the SIMPLE SWITCHER line of switching regulators. LM267X Made Simple is available on (version 6.0) Windows 3.1, NT, or 95 operating systems. Given: Given: VOUT = Regulated Output Voltage VOUT = 20V VIN(max) = Maximum Input Voltage VIN(max) = 28V ILOAD(max) = Maximum Load Current ILOAD(max) = 500 mA F = Switching Frequency (Fixed at a nominal 260 kHz). F = Switching Frequency (Fixed at a nominal 260 kHz). 1. Programming Output Voltage (Selecting R1 and R2, as shown 1. Programming Output Voltage (Selecting R1 and R2, as shown in Figure 3) in Figure 3) Use the following formula to select the appropriate resistor values. Select R1 to be 1 kΩ, 1%. Solve for R2. www.national.com 16 EXAMPLE (Adjustable Output Voltage Version) where VREF = 1.21V Select a value for R1 between 240Ω and 1.5 kΩ. The lower resistor R2 = 1 kΩ (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ. values minimize noise pickup in the sensitive feedback pin. (For the R2 = 15.4 kΩ. lowest temperature coefficient and the best stability with time, use 1% metal film resistors.) 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant E • T (V • μs), from the following formula: 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant (E • T), where VSAT=internal switch saturation voltage=0.25V and VD = diode forward voltage drop = 0.5V B. Use the E • T value from the previous formula and match it with B. E • T = 21.6 (V • μs) the E • T number on the vertical axis of the Inductor Value Selection Guide shown in Figure 7. C. On the horizontal axis, select the maximum load current. C. ILOAD(max) = 500 mA D. Identify the inductance region intersected by the E • T value and D. From the inductor value selection guide shown in Figure 7, the the Maximum Load Current value. Each region is identified by an inductance region intersected by the 21.6 (V • μs) horizontal line inductance value and an inductor code (LXX). and the 500 mA vertical line is 100 μH, and the inductor code is L20. E. Select an appropriate inductor from the four manufacturer's part E. From the table in Figure 8, locate line L20, and select an inductor numbers listed in Figure 8. For information on the different types of part number from the list of manufacturers' part numbers. inductors, see the inductor selection in the fixed output voltage design procedure. 3. Output Capacitor SeIection (COUT) 3. Output Capacitor SeIection (COUT) A. Select an output capacitor from the capacitor code selection A. Use the appropriate row of the capacitor code selection guide, guide in Figure 16. Using the inductance value found in the inductor in Figure 16. For this example, use the 15–20V row. The capacitor selection guide, step 1, locate the appropriate capacitor code code corresponding to an inductance of 100 μH is C20. corresponding to the desired output voltage. B. Select an appropriate capacitor value and voltage rating, using B. From the output capacitor selection table in Figure 17, choose the capacitor code, from the output capacitor selection table in a capacitor value (and voltage rating) that intersects the capacitor Figure 17. There are two solid tantalum (surface mount) capacitor code(s) selected in section A, C20. manufacturers and four electrolytic (through hole) capacitor The capacitance and voltage rating values corresponding to the manufacturers to choose from. It is recommended that both the capacitor code C20 are the: manufacturers and the manufacturer's series that are listed in the Surface Mount: table be used. A table listing the manufacturers' phone numbers is 33 μF/25V Sprague 594D Series. located in Figure 11. 33 μF/25V AVX TPS Series. Through Hole: 33 μF/25V Sanyo OS-CON SC Series. 120 μF/35V Sanyo MV-GX Series. 120 μF/35V Nichicon PL Series. 120 μF/35V Panasonic HFQ Series. Other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100 kHz ESR) closely match the characteristics of the capacitors listed in the output capacitor table. Refer to the capacitor manufacturers' data sheet for this information. 17 www.national.com LM2671 PROCEDURE (Adjustable Output Voltage Version) LM2671 PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) 4. Catch Diode Selection (D1) A. In normal operation, the average current of the catch diode is the load current times the catch diode duty cycle, 1-D (D is the switch duty cycle, which is approximately VOUT/VIN). The largest value of the catch diode average current occurs at the maximum input voltage (minimum D). For normal operation, the catch diode current rating must be at least 1.3 times greater than its maximum average current. However, if the power supply design must withstand a continuous output short, the diode should have a current rating greater than the maximum current limit of the LM2671. The most stressful condition for this diode is a shorted output condition. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. C. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best performance and efficiency. The Schottky diode must be located close to the LM2671 using short leads and short printed circuit traces. 5. Input Capacitor (CIN) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input. This capacitor should be located close to the IC using short leads. In addition, the RMS current rating of the input capacitor should be selected to be at least ½ the DC load current. The capacitor manufacturer data sheet must be checked to assure that this current rating is not exceeded. The curves shown in Figure 14 show typical RMS current ratings for several different aluminum electrolytic capacitor values. A parallel connection of two or more capacitors may be required to increase the total minimum RMS current rating to suit the application requirements. For an aluminum electrolytic capacitor, the voltage rating should be at least 1.25 times the maximum input voltage. Caution must be exercised if solid tantalum capacitors are used. The tantalum capacitor voltage rating should be twice the maximum input voltage. The tables in Figure 15 show the recommended application voltage for AVX TPS and Sprague 594D tantalum capacitors. It is also recommended that they be surge current tested by the manufacturer. The TPS series available from AVX, and the 593D and 594D series from Sprague are all surge current tested. Another approach to minimize the surge current stresses on the input capacitor is to add a small inductor in series with the input supply line. Use caution when using ceramic capacitors for input bypassing, because it may cause severe ringing at the VIN pin. 4. Catch Diode Selection (D1) A. Refer to the table shown in Figure 12. Schottky diodes provide the best performance, and in this example a 1A, 40V Schottky diode would be a good choice. If the circuit must withstand a continuous shorted output, a higher current (at least 1.2A) Schottky diode is recommended. 5. Input Capacitor (CIN) The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 28V, an aluminum electrolytic capacitor with a voltage rating of at least 35V (1.25 × VIN) would be needed. The RMS current rating requirement for the input capacitor in a buck regulator is approximately ½ the DC load current. In this example, with a 500 mA load, a capacitor with a RMS current rating of at least 250 mA is needed. The curves shown in Figure 14 can be used to select an appropriate input capacitor. From the curves, locate the 35V line and note which capacitor values have RMS current ratings greater than 250 mA. For a through hole design, a 68 μF/35V electrolytic capacitor (Panasonic HFQ series, Nichicon PL, Sanyo MV-GX series or equivalent) would be adequate. Other types or other manufacturers' capacitors can be used provided the RMS ripple current ratings are adequate. Additionally, for a complete surface mount design, electrolytic capacitors such as the Sanyo CV-C or CV-BS and the Nichicon WF or UR and the NIC Components NACZ series could be considered. For surface mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating and voltage rating. In this example, checking Figure 15, and the Sprague 594D series datasheet, a Sprague 594D 15 μF, 50V capacitor is adequate. 6. Boost Capacitor (CB) 6. Boost Capacitor (CB) This capacitor develops the necessary voltage to turn the switch For this application, and all applications, use a 0.01 μF, 50V gate on fully. All applications should use a 0.01 μF, 50V ceramic ceramic capacitor. capacitor. If the soft-start and frequency synchronization features are desired, look at steps 6 and 7 in the fixed output design procedure. Inductance (μH) Case Style (Note 7) Output Voltage (V) 22 33 47 68 100 150 220 SM and TH 1.21–2.50 — — — — C1 C2 C3 SM and TH 2.50–3.75 — — — C1 C2 C3 C3 www.national.com 18 Output Voltage (V) 22 33 47 68 100 150 220 SM and TH 3.75–5.0 — — C4 C5 C6 C6 C6 SM and TH 5.0–6.25 — C4 C7 C6 C6 C6 C6 SM and TH 6.25–7.5 C8 C4 C7 C6 C6 C6 C6 SM and TH 7.5–10.0 C9 C10 C11 C12 C13 C13 C13 SM and TH 10.0–12.5 C14 C11 C12 C12 C13 C13 C13 SM and TH 12.5–15.0 C15 C16 C17 C17 C17 C17 C17 SM and TH 15.0–20.0 C18 C19 C20 C20 C20 C20 C20 SM and TH 20.0–30.0 C21 C22 C22 C22 C22 C22 C22 TH 30.0–37.0 C23 C24 C24 C25 C25 C25 C25 Note 7: SM - Surface Mount, TH - Through Hole FIGURE 16. Capacitor Code Selection Guide Output Capacitor Surface Mount Through Hole Cap. Ref. Desg. # Sprague 594D Series AVX TPS Series Sanyo OS-CON SA Series Sanyo MV-GX Series Nichicon PL Series Panasonic HFQ Series (μF/V) (μF/V) (μF/V) (μF/V) (μF/V) (μF/V) C1 120/6.3 100/10 100/10 220/35 220/35 220/35 C2 120/6.3 100/10 100/10 150/35 150/35 150/35 C3 120/6.3 100/10 100/35 120/35 120/35 120/35 C4 68/10 100/10 68/10 220/35 220/35 220/35 C5 100/16 100/10 100/10 150/35 150/35 150/35 C6 100/16 100/10 100/10 120/35 120/35 120/35 C7 68/10 100/10 68/10 150/35 150/35 150/35 C8 100/16 100/10 100/10 330/35 330/35 330/35 C9 100/16 100/16 100/16 330/35 330/35 330/35 C10 100/16 100/16 68/16 220/35 220/35 220/35 C11 100/16 100/16 68/16 150/35 150/35 150/35 C12 100/16 100/16 68/16 120/35 120/35 120/35 C13 100/16 100/16 100/16 120/35 120/35 120/35 C14 100/16 100/16 100/16 220/35 220/35 220/35 C15 47/20 68/20 47/20 220/35 220/35 220/35 C16 47/20 68/20 47/20 150/35 150/35 150/35 C17 47/20 68/20 47/20 120/35 120/35 120/35 C18 68/25 (2×) 33/25 47/25 (Note 8) 220/35 220/35 220/35 C19 33/25 33/25 33/25 (Note 8) 150/35 150/35 150/35 C20 33/25 33/25 33/25 (Note 8) 120/35 120/35 120/35 C21 33/35 (2×) 22/25 (Note 9) 150/35 150/35 150/35 C22 33/35 22/35 (Note 9) 120/35 120/35 120/35 C23 (Note 9) (Note 9) (Note 9) 220/50 100/50 120/50 C24 (Note 9) (Note 9) (Note 9) 150/50 100/50 120/50 C25 (Note 9) (Note 9) (Note 9) 150/50 82/50 82/50 Note 8: The SC series of Os-Con capacitors (others are SA series) Note 9: The voltage ratings of the surface mount tantalum chip and Os-Con capacitors are too low to work at these voltages. FIGURE 17. Output Capacitor Selection Table 19 www.national.com LM2671 Inductance (μH) Case Style (Note 7) LM2671 Application Information TYPICAL SURFACE MOUNT PC BOARD LAYOUT, FIXED OUTPUT (4X SIZE) 10004239 CIN - 15 μF, 25V, Solid Tantalum Sprague, “594D series” COUT - 68 μF, 10V, Solid Tantalum Sprague, “594D series” D1 - 1A, 40V Schottky Rectifier, Surface Mount L1 - 47 μH, L13, Coilcraft DO3308 CB - 0.01 μF, 50V, Ceramic TYPICAL SURFACE MOUNT PC BOARD LAYOUT, ADJUSTABLE OUTPUT (4X SIZE) 10004240 CIN - 15 μF, 50V, Solid Tantalum Sprague, “594D series” COUT - 33 μF, 25V, Solid Tantalum Sprague, “594D series” D1 - 1A, 40V Schottky Rectifier, Surface Mount L1 - 100 μH, L20, Coilcraft DO3316 CB - 0.01 μF, 50V, Ceramic R1 - 1k, 1% R2 - Use formula in Design Procedure FIGURE 18. PC Board Layout Layout is very important in switching regulator designs. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicated by heavy lines (in Figure 2 and Figure 3) should be wide printed circuit traces and should be kept as short as possible. For best results, external components should be located as close to the switcher IC as possible using ground plane construction or single point grounding. www.national.com If open core inductors are used, special care must be taken as to the location and positioning of this type of inductor. Allowing the inductor flux to intersect sensitive feedback, IC ground path, and COUT wiring can cause problems. When using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. 20 21 www.national.com LM2671 The Die Attach Pad (DAP) can and should be connected to PCB Ground plane/island. For CAD and assembly guidelines refer to Application Note AN-1187 at http:// power.national.com. LLP PACKAGE DEVICES The LM2671 is offered in the 16 lead LLP surface mount package to allow for increased power dissipation compared to the SO-8 and DIP. LM2671 Physical Dimensions inches (millimeters) unless otherwise noted 8-Lead (0.150″ Wide) Molded Small Outline Package, JEDEC Order Number LM2671M-3.3, LM2671M-5.0, LM2671M-12 or LM2671M-ADJ NS Package Number M08A www.national.com 22 LM2671 8-Lead (0.300″ Wide) Molded Dual-In-Line Package Order Number LM2671N-3.3, LM2671N-5.0, LM2671N-12 or LM2671N-ADJ NS Package Number N08E 16-Lead LLP Surface Mount Package NS Package Number LDA16A 23 www.national.com LM2671 SIMPLE SWITCHER Power Converter High Efficiency 500mA Step-Down Voltage Regulator with Features THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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