LM2675LDX-3.3

LM2675 SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator June 2005 LM2675 SIMPLE SWITCHER ® Power Converter High Efficiency 1A Step-Down Voltage Regulator General Description The LM2675 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 1A 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) and a fixed frequency oscillator. The LM2675 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 LM2675 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 LM2675 buck regulator design procedure, there exists computer design software, LM267X Made Simple version 6.0. Features n Efficiency up to 96% n Available in SO-8, 8-pin DIP and LLP packages n Computer Design Software LM267X Made Simple (version 6.0) n Simple and easy to design with n Requires only 5 external components n Uses readily available standard inductors n 3.3V, 5.0V, 12V, and adjustable output versions n Adjustable version output voltage range: 1.21V to 37V n ± 1.5% max output voltage tolerance over line and load conditions n Guaranteed 1A output load current n 0.25Ω DMOS Output Switch n Wide input voltage range: 8V to 40V n 260 kHz fixed frequency internal oscillator n TTL shutdown capability, low power standby mode n Thermal shutdown and current limit protection Typical Applications n Simple High Efficiency ( > 90%) Step-Down (Buck) Regulator n Efficient Pre-Regulator for Linear Regulators n Positive-to-Negative Converter Typical Application 01280301 SIMPLE SWITCHER ® is a registered trademark of National Semiconductor Corporation. Windows ® is a registered trademark of Microsoft Corporation. © 2005 National Semiconductor Corporation DS012803 www.national.com LM2675 Connection Diagrams 16-Lead LLP Surface Mount Package Top View 8-Lead Package Top View 01280302 SO-8/DIP Package See NSC Package Drawing Number MO8A/N08E 01280338 LLP Package See NSC Package Drawing Number LDA16A Package Marking and Ordering Information TABLE 1. Output Voltage 16 Lead LLP 12 12 3.3 3.3 5.0 5.0 ADJ ADJ SO-8 12 12 3.3 3.3 5.0 5.0 ADJ ADJ DIP 12 3.3 5.0 ADJ LM2675N-12 LM2675N-3.3 LM2675N-5.0 LM2675N-ADJ LM2675N-12 LM2675N-3.3 LM2675N-5.0 LM2675N-ADJ Shipped in Anti-Static Rails Shipped in Anti-Static Rails Shipped in Anti-Static Rails Shipped in Anti-Static Rails LM2675M-12 LM2675MX-12 LM2675M-3.3 LM2675MX-3.3 LM2675M-5.0 LM2675MX-5.0 LM2675M-ADJ LM2675MX-ADJ 2675M-12 2675M-12 2675M-3.3 2675M-3.3 2675M-5.0 2675M-5.0 2675M-ADJ 2675M-ADJ Shipped in Anti-Static Rails 2500 Units on Tape and Reel Shipped in Anti-Static Rails 2500 Units on Tape and Reel Shipped in Anti-Static Rails 2500 Units on Tape and Reel Shipped in Anti-Static Rails 2500 Units on Tape and Reel LM2675LD-12 LM2675LDX-12 LM2675LD-3.3 LM2675LDX-3.3 LM2675LD-5.0 LM2675LDX-5.0 LM2675LD-ADJ LM2675LDX-ADJ S000DB S000DB S000EB S000EB S000FB S000FB S000GB S000GB 1000 Units on Tape and Reel 4500 Units on Tape and Reel 1000 Units on Tape and Reel 4500 Units on Tape and Reel 1000 Units on Tape and Reel 4500 Units on Tape and Reel 1000 Units on Tape and Reel 4500 Units on Tape and Reel Order Information Package Marking Supplied as: www.national.com 2 LM2675 Absolute Maximum Ratings (Note 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage ON/OFF Pin Voltage Switch Voltage to Ground Boost Pin Voltage Feedback Pin Voltage ESD Susceptibility Human Body Model (Note 2) Power Dissipation 2 kV Internally Limited 45V −0.1V ≤ VSH ≤ 6V −1V VSW + 8V −0.3V ≤ VFB ≤ 14V Storage Temperature Range Lead Temperature M Package Vapor Phase (60s) Infrared (15s) N Package (Soldering, 10s) LLP Package (See AN-1187) Maximum Junction Temperature +150˚C +215˚C +220˚C +260˚C −65˚C to +150˚C Operating Ratings Supply Voltage 6.5V to 40V Junction Temperature Range −40˚C ≤ TJ ≤ +125˚C Electrical Characteristics LM2675-3.3 Specifications with standard type face are for TJ = 25˚C, and those with bold type face apply over full Operating Temperature Range. Symbol Parameter Conditions Typical (Note 4) SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT VOUT η Output Voltage Output Voltage Efficiency VIN = 8V to 40V, ILOAD = 20 mA to 1A VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA VIN = 12V, ILOAD = 1A 3.3 3.3 86 3.251/3.201 3.251/3.201 3.350/3.399 3.350/3.399 V V % Min (Note 5) Max (Note 5) Units LM2675-5.0 Symbol Parameter Conditions Typical (Note 4) SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT VOUT η Output Voltage Output Voltage Efficiency VIN = 8V to 40V, ILOAD = 20 mA to 1A VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA VIN = 12V, ILOAD = 1A 5.0 5.0 90 4.925/4.850 4.925/4.850 5.075/5.150 5.075/5.150 V V % Min (Note 5) Max (Note 5) Units LM2675-12 Symbol Parameter Conditions Typical (Note 4) SYSTEM PARAMETERS Test Circuit Figure 2 (Note 3) VOUT η Output Voltage Efficiency VIN = 15V to 40V, ILOAD = 20 mA to 1A VIN = 24V, ILOAD = 1A 12 94 11.82/11.64 12.18/12.36 V % Min (Note 5) Max (Note 5) Units LM2675-ADJ Symbol Parameter Conditions Typ (Note 4) SYSTEM PARAMETERS Test Circuit Figure 3 (Note 3) VFB Feedback Voltage Feedback Voltage VIN = 8V to 40V, ILOAD = 20 mA to 1A VOUT Programmed for 5V (see Circuit of Figure 3) VIN = 6.5V to 40V, ILOAD = 20 mA to 500 mA VOUT Programmed for 5V (see Circuit of Figure 3) 1.210 1.192/1.174 1.228/1.246 V Min (Note 5) Max (Note 5) Units VFB 1.210 1.192/1.174 1.228/1.246 V 3 www.national.com LM2675 LM2675-ADJ Symbol η Parameter Efficiency (Continued) Conditions VIN = 12V, ILOAD = 1A Typ (Note 4) 90 Min (Note 5) Max (Note 5) % Units All Output Voltage Versions Specifications with standard type face are for TJ = 25˚C, and those with 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 IQ Parameters Quiescent Current Conditions VFEEDBACK = 8V For 3.3V, 5.0V, and ADJ Versions VFEEDBACK = 15V For 12V Versions ISTBY ICL IL Standby Quiescent Current Current Limit Output Leakage Current VIN = 40V, ON/OFF Pin = 0V VSWITCH = 0V VSWITCH = −1V, ON/OFF Pin = 0V RDS(ON) fO D IBIAS VS/D IS/D θJA Switch On-Resistance Oscillator Frequency Maximum Duty Cycle Minimum Duty Cycle Feedback Bias Current ON/OFF Pin Voltage Thesholds ON/OFF Pin Current Thermal Resistance ON/OFF Pin = 0V N Package, Junction to Ambient (Note 6) M Package, Junction to Ambient (Note 6) VFEEDBACK = 1.3V ADJ Version Only ISWITCH = 1A Measured at Switch Pin ON/OFF Pin = 0V 50 1.55 1 6 0.25 260 95 0 85 1.4 20 95 105 0.8 7 2.0 37 225 1.25/1.2 100/150 2.1/2.2 25 15 0.30/0.50 275 µA A µA mA Ω kHz % % nA V µA ˚C/W 2.5 mA Typ 2.5 Min Max 3.6 Units mA DEVICE PARAMETERS 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 LM2675 is used as shown in Figures 2, 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 software (version 6.0). 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 LM2675 Typical Performance Characteristics Normalized Output Voltage Line Regulation 01280303 01280304 Efficiency Drain-to-Source Resistance 01280305 01280306 Switch Current Limit Operating Quiescent Current 01280307 01280308 5 www.national.com LM2675 Typical Performance Characteristics Standby Quiescent Current (Continued) ON/OFF Threshold Voltage 01280309 01280310 ON/OFF Pin Current (Sourcing) Switching Frequency 01280311 01280312 Feedback Pin Bias Current Peak Switch Current 01280313 01280314 www.national.com 6 LM2675 Typical Performance Characteristics Dropout Voltage — 3.3V Option (Continued) Dropout Voltage — 5.0V Option 01280315 01280316 Block Diagram 01280317 * Active Inductor Patent Number 5,514,947 † Active Capacitor Patent Number 5,382,918 FIGURE 1. 7 www.national.com LM2675 Typical Performance Characteristics Continuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 1A L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ (Circuit of Figure 2) Discontinuous Mode Switching Waveforms VIN = 20V, VOUT = 5V, ILOAD = 300 mA L = 15 µH, COUT = 68 µF (2x), COUTESR = 25 mΩ 01280318 01280319 A: VSW Pin Voltage, 10 V/div. B: Inductor Current, 0.5 A/div C: Output Ripple Voltage, 20 mV/div AC-Coupled 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 Load Transient Response for Continuous Mode VIN = 20V, VOUT = 5V, ILOAD = 1A L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ Horizontal Time Base: 1 µs/div Load Transient Response for Discontinuous Mode VIN = 20V, VOUT = 5V, L = 47 µH, COUT = 68 µF, COUTESR = 50 mΩ 01280320 01280321 A: Output Voltage, 100 mV/div, AC-Coupled. B: Load Current: 200 mA to 1A Load Pulse A: Output Voltage, 100 mV/div, AC-Coupled. B: Load Current: 100 mA to 400 mA Load Pulse Horizontal Time Base: 50 µs/div Horizontal Time Base: 200 µs/div www.national.com 8 LM2675 Test Circuit and Layout Guidelines 01280322 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 01280323 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 Version 9 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (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: VOUT = Regulated Output Voltage (3.3V, 5V, or 12V) VIN(max) = Maximum DC Input Voltage ILOAD(max) = Maximum Load Current 1. Inductor Selection (L1) A. Select the correct inductor value selection guide from Figure 4, 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. 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 33 µH. The capacitance and voltage rating values corresponding to the 33 µH inductor are the: Given: VOUT = 5V VIN(max) = 12V ILOAD(max) = 1A 1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown in Figure 5. EXAMPLE (Fixed Output Voltage Version) B. From the inductor value selection guide shown in Figure 5, the inductance region intersected by the 12V horizontal line and the 1A vertical line is 33 µH, and the inductor code is L23. C. The inductance value required is 33 µH. From the table in Figure 8, go to the L23 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.) www.national.com 10 LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (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. 3. 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 the output voltage divided by the input voltage). The largest value of the catch diode average 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 LM2675. 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 LM2675 using short leads and short printed circuit traces. 4. Input Capacitor (CIN) 4. Input Capacitor (CIN) Surface Mount: 68 µF/10V Sprague 594D Series. 100 µF/10V AVX TPS Series. Through Hole: 68 µF/10V Sanyo OS-CON SA Series. 220 µF/35V Sanyo MV-GX Series. 220 µF/35V Nichicon PL Series. 220 µF/35V Panasonic HFQ Series. (Continued) EXAMPLE (Fixed Output Voltage Version) 3. Catch Diode Selection (D1) A. Refer to the table shown in Figure 12. In this example, a 1A, 20V Schottky diode will provide the best performance. If the circuit must withstand a continuous shorted output, a higher current Schottky diode is recommended. 11 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (Fixed Output Voltage Version) 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 1⁄2 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. 5. Boost Capacitor (CB) (Continued) EXAMPLE (Fixed Output Voltage Version) The important parameters for the input capacitor are the input voltage rating and the RMS current rating. With a maximum input voltage of 12V, an aluminum electrolytic capacitor with a voltage rating greater than 15V (1.25 x VIN) would be needed. The next higher capacitor voltage rating is 16V. The RMS current rating requirement for the input capacitor in a buck regulator is approximately 1⁄2 the DC load current. In this example, with a 1A load, a capacitor with a RMS current rating of at least 500 mA is needed. The curves shown in Figure 14 can be used to select an appropriate input capacitor. From the curves, locate the 16V line and note which capacitor values have RMS current ratings greater than 500 mA. For a through hole design, a 330 µF/16V 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, 25V capacitor is adequate. 5. 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. www.national.com 12 LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) Inductor Value Selection Guides (For Continuous Mode Operation) (Continued) 01280326 01280328 FIGURE 4. LM2675-3.3 FIGURE 6. LM2675-12 01280327 FIGURE 5. LM2675-5.0 FIGURE 7. LM2675-ADJ 01280329 13 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) Ind. Inductance Current Ref. (µH) (A) Desg. L4 L5 L6 L7 L9 L10 L11 L12 L13 L14 L15 L18 L19 L20 L21 L22 L23 L24 L27 L28 L29 L30 68 47 33 22 220 150 100 68 47 33 22 220 150 100 68 47 33 22 220 150 100 68 0.32 0.37 0.44 0.52 0.32 0.39 0.48 0.58 0.70 0.83 0.99 0.55 0.66 0.82 0.99 1.17 1.40 1.70 1.00 1.20 1.47 1.78 Schott Through Hole Surface Mount Hole RL-1284-68-43 RL-1284-47-43 RL-1284-33-43 RL-1284-22-43 RL-5470-3 RL-5470-4 RL-5470-5 RL-5470-6 RL-5470-7 RL-1284-33-43 RL-1284-22-43 RL-5471-2 RL-5471-3 RL-5471-4 RL-5471-5 RL-5471-6 RL-5471-7 RL-1283-22-43 RL-5471-2 RL-5471-3 RL-5471-4 RL-5471-5 Renco Through Surface Mount RL1500-68 RL1500-47 RL1500-33 RL1500-22 Pulse Engineering Through Hole Surface Mount (Continued) Coilcraft Surface Mount 67143940 67144310 67148310 67148420 67148320 67148430 67148330 67148440 67143960 67144330 67143970 67144340 67143980 67144350 67143990 67144360 67144000 67144380 67148340 67148450 67148350 67148460 67144040 67144420 67144050 67144430 67144060 67144440 67144070 67144450 67144080 67144460 67144090 67144470 67148370 67148480 67144110 67144490 67144120 67144500 67144130 67144510 67144140 67144520 PE-53804 PE-53804-S DO1608-683 PE-53805 PE-53805-S DO1608-473 PE-53806 PE-53806-S DO1608-333 PE-53807 PE-53807-S DO1608-223 RL1500-220 PE-53809 PE-53809-S DO3308-224 RL1500-150 PE-53810 PE-53810-S DO3308-154 RL1500-100 PE-53811 PE-53811-S DO3308-104 RL1500-68 RL1500-47 RL1500-33 RL1500-22 PE-53812 PE-53812-S DO3308-683 PE-53813 PE-53813-S DO3308-473 PE-53814 PE-53814-S DO3308-333 PE-53815 PE-53815-S DO3308-223 RL1500-220 PE-53818 PE-53818-S DO3316-224 RL1500-150 PE-53819 PE-53819-S DO3316-154 RL1500-100 PE-53820 PE-53820-S DO3316-104 RL1500-68 — — — — — — — PE-53821 PE-53821-S DO3316-683 PE-53822 PE-53822-S DO3316-473 PE-53823 PE-53823-S DO3316-333 PE-53824 PE-53824-S DO3316-223 PE-53827 PE-53827-S PE-53828 PE-53828-S PE-53829 PE-53829-S PE-53830 PE-53830-S DO5022P-224 DO5022P-154 DO5022P-104 DO5022P-683 FIGURE 8. Inductor Manufacturers’ Part Numbers Coilcraft Inc. Coilcraft Inc., Europe Pulse Engineering Inc. Pulse Engineering Inc., Europe Renco Electronics Inc. Schott Corp. Phone FAX Phone FAX Phone FAX Phone FAX Phone FAX Phone FAX (800) 322-2645 (708) 639-1469 +44 1236 730 595 +44 1236 730 627 (619) 674-8100 (619) 674-8262 +353 93 24 107 +353 93 24 459 (800) 645-5828 (516) 586-5562 (612) 475-1173 (612) 475-1786 FIGURE 9. Inductor Manufacturers’ Phone Numbers www.national.com 14 LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) Output Capacitor Output Voltage (V) Inductance (µH) Surface Mount Sprague 594D Series (µF/V) 22 33 3.3 47 68 100 150 22 33 5.0 47 68 100 150 22 33 47 12 68 100 150 220 120/6.3 120/6.3 68/10 120/6.3 120/6.3 120/6.3 100/16 68/10 68/10 100/16 100/16 100/16 120/20 68/25 47/20 47/20 47/20 47/20 47/20 AVX TPS Series (µF/V) 100/10 100/10 100/10 100/10 100/10 100/10 100/10 10010 100/10 100/10 100/10 100/10 (2x) 68/20 68/20 68/20 68/20 68/20 68/20 68/20 Sanyo OS-CON SA Series (µF/V) 100/10 68/10 68/10 100/10 100/10 100/10 100/10 68/10 68/10 100/10 100/10 100/10 68/20 68/20 47/20 47/20 47/20 47/20 47/20 Through Hole Sanyo MV-GX Series (µF/V) 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 120/35 Nichicon PL Series (µF/V) 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 120/35 (Continued) Panasonic HFQ Series (µF/V) 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 330/35 220/35 150/35 120/35 120/35 120/35 120/35 FIGURE 10. Output Capacitor Table Nichicon Corp. Panasonic AVX Corp. Sprague/Vishay Sanyo Corp. Phone FAX Phone FAX Phone FAX Phone FAX Phone FAX (847) 843-7500 (847) 843-2798 (714) 373-7857 (714) 373-7102 (803) 448-9411 (803) 448-1943 (207) 324-4140 (207) 324-7223 (619) 661-6322 (619) 661-1055 FIGURE 11. Capacitor Manufacturers’ Phone Numbers 15 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) 1A Diodes VR 20V 30V Surface Mount SK12 B120 SK13 B130 MBRS130 40V SK14 B140 MBRS140 10BQ040 10MQ040 15MQ040 50V SK15 B150 10BQ050 MBR150 11DQ05 SR105 SK35 30WQ05F MBR350 31DQ05 SR305 Through Hole 1N5817 SR102 1N5818 11DQ03 SR103 1N5819 11DQ04 SR104 SK34 30BQ040 30WQ04F MBRS340 MBRD340 1N5822 MBR340 31DQ04 SR304 SK33 30WQ03F 3A Diodes Surface Mount SK32 Through Hole 1N5820 SR302 1N5821 31DQ03 (Continued) FIGURE 12. Schottky Diode Selection Table International Rectifier Corp. Motorola, Inc. General Instruments Corp. Diodes, Inc. Phone FAX Phone FAX Phone FAX Phone FAX (310) 322-3331 (310) 322-3332 (800) 521-6274 (602) 244-6609 (516) 847-3000 (516) 847-3236 (805) 446-4800 (805) 446-4850 FIGURE 13. Diode Manufacturers’ Phone Numbers 01280330 FIGURE 14. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical) www.national.com 16 LM2675 LM2675 Series Buck Regulator Design Procedure (Fixed Output) AVX TPS Recommended Application Voltage 3.3 5 10 12 15 Sprague 594D Recommended Application Voltage 2.5 3.3 5 8 12 18 24 29 FIGURE 15. Voltage Rating 4 6.3 10 16 20 25 35 50 Voltage Rating 6.3 10 20 25 35 (Continued) +85˚C Rating +85˚C Rating LM2675 Series Buck Regulator Design Procedure (Adjustable Output) PROCEDURE (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 version 6.0 is available for use on Windows 3.1, NT, or 95 operating systems. Given: VOUT = Regulated Output Voltage VIN(max) = Maximum Input Voltage ILOAD(max) = Maximum Load Current F = Switching Frequency (Fixed at a nominal 260 kHz). 1. Programming Output Voltage (Selecting R1 and R2, as shown in Figure 3) Use the following formula to select the appropriate resistor values. Given: VOUT = 20V VIN(max) = 28V ILOAD(max) = 1A F = Switching Frequency (Fixed at a nominal 260 kHz). 1. Programming Output Voltage (Selecting R1 and R2, as shown in Figure 3) Select R1 to be 1 kΩ, 1%. Solve for R2. EXAMPLE (Adjustable Output Voltage Version) where VREF = 1.21V Select a value for R1 between 240Ω and 1.5 kΩ. The lower R2 = 1k (16.53 − 1) = 15.53 kΩ, closest 1% value is 15.4 kΩ. resistor values minimize noise pickup in the sensitive feedback R2 = 15.4 kΩ. pin. (For the lowest temperature coefficient and the best stability with time, use 1% metal film resistors.) 17 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Adjustable Output) (Continued) PROCEDURE (Adjustable Output Voltage Version) 2. Inductor Selection (L1) EXAMPLE (Adjustable Output Voltage Version) 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant E • T (V • A. Calculate the inductor Volt • microsecond constant (E • T), µs), from the following formula: 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 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. D. Identify the inductance region intersected by the E • T value and the Maximum Load Current value. Each region is identified by an inductance value and an inductor code (LXX). E. Select an appropriate inductor from the four manufacturer’s part numbers listed in Figure 8. For information on the different types of inductors, see the inductor selection in the fixed output voltage design procedure. 3. Output Capacitor Selection (COUT) B. E • T = 21.6 (V • µs) C. ILOAD(max) = 1A D. From the inductor value selection guide shown in Figure 7, the inductance region intersected by the 21.6 (V • µs) horizontal line and the 1A vertical line is 68 µH, and the inductor code is L30. E. From the table in Figure 8, locate line L30, and select an inductor part number from the list of manufacturers part numbers. 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 in Figure 16. Using the inductance value found in the guide, in Figure 16. For this example, use the 15–20V row. The inductor selection guide, step 1, locate the appropriate capacitor capacitor code corresponding to an inductance of 68 µH is C20. code corresponding to the desired output voltage. B. Select an appropriate capacitor value and voltage rating, using the capacitor code, from the output capacitor selection table in Figure 17. There are two solid tantalum (surface mount) capacitor manufacturers and four electrolytic (through hole) capacitor manufacturers to choose from. 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. B. From the output capacitor selection table in Figure 17, choose a capacitor value (and voltage rating) that intersects the capacitor code(s) selected in section A, C20. The capacitance and voltage rating values corresponding to the capacitor code C20 are the: Surface Mount: 33 µF/25V Sprague 594D Series. 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. www.national.com 18 LM2675 LM2675 Series Buck Regulator Design Procedure (Adjustable Output) (Continued) PROCEDURE (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 LM2675. 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 LM2675 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 1⁄2 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. 6. Boost Capacitor (CB) 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 x VIN) would be needed. The RMS current rating requirement for the input capacitor in a buck regulator is approximately 1⁄2 the DC load current. In this example, with a 1A load, a capacitor with a RMS current rating of at least 500 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 500 mA. For a through hole design, a 330 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. EXAMPLE (Adjustable Output Voltage Version) 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 2.2A) Schottky diode is recommended. 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. 19 www.national.com LM2675 LM2675 Series Buck Regulator Design Procedure (Adjustable Output) (Continued) Case Style (Note 7) SM and TH SM and TH SM and TH SM and TH SM and TH SM and TH SM and TH SM and TH SM and TH SM and TH TH Output Voltage (V) 1.21–2.50 2.50–3.75 3.75–5.0 5.0–6.25 6.25–7.5 7.5–10.0 10.0–12.5 12.5–15.0 15.0–20.0 20.0–30.0 30.0–37.0 TH - Through Hole Inductance (µH) 22 — — — — C8 C9 C14 C15 C18 C21 C23 33 — — — C4 C4 C10 C11 C16 C19 C22 C24 47 — — C4 C7 C7 C11 C12 C17 C20 C22 C24 68 — C1 C5 C6 C6 C12 C12 C17 C20 C22 C25 100 C1 C2 C6 C6 C6 C13 C13 C17 C20 C22 C25 150 C2 C3 C6 C6 C6 C13 C13 C17 C20 C22 C25 220 C3 C3 C6 C6 C6 C13 C13 C17 C20 C22 C25 Note 7: SM - Surface Mount, FIGURE 16. Capacitor Code Selection Guide www.national.com 20 LM2675 LM2675 Series Buck Regulator Design Procedure (Adjustable Output) (Continued) Output Capacitor Cap. Ref. Desg. # C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 C25 Surface Mount Sprague 594D Series (µF/V) 120/6.3 120/6.3 120/6.3 68/10 100/16 100/16 68/10 100/16 100/16 100/16 100/16 100/16 100/16 100/16 47/20 47/20 47/20 68/25 33/25 33/25 33/35 33/35 (Note 9) (Note 9) (Note 9) AVX TPS Series (µF/V) 100/10 100/10 100/10 100/10 100/10 100/10 100/10 100/10 100/16 100/16 100/16 100/16 100/16 100/16 68/20 68/20 68/20 (2x) 33/25 33/25 33/25 (2x) 22/25 22/35 (Note 9) (Note 9) (Note 9) Sanyo OS-CON SA Series (µF/V) 100/10 100/10 100/35 68/10 100/10 100/10 68/10 100/10 100/16 68/16 68/16 68/16 100/16 100/16 47/20 47/20 47/20 47/25 (Note 8) 33/25 (Note 8) 33/25 (Note 8) (Note 9) (Note 9) (Note 9) (Note 9) (Note 9) Through Hole Sanyo MV-GX Series (µF/V) 220/35 150/35 120/35 220/35 150/35 120/35 150/35 330/35 330/35 220/35 150/35 120/35 120/35 220/35 220/35 150/35 120/35 220/35 150/35 120/35 150/35 120/35 220/50 150/50 150/50 Nichicon PL Series (µF/V) 220/35 150/35 120/35 220/35 150/35 120/35 150/35 330/35 330/35 220/35 150/35 120/35 120/35 220/35 220/35 150/35 120/35 220/35 150/35 120/35 150/35 120/35 100/50 100/50 82/50 Panasonic HFQ Series (µF/V) 220/35 150/35 120/35 220/35 150/35 120/35 150/35 330/35 330/35 220/35 150/35 120/35 120/35 220/35 220/35 150/35 120/35 220/35 150/35 120/35 150/35 120/35 120/50 120/50 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 21 www.national.com LM2675 Application Information TYPICAL SURFACE MOUNT PC BOARD LAYOUT, FIXED OUTPUT (4X SIZE) 01280336 CIN - 15 µF, 50V, Solid Tantalum Sprague, “594D series” COUT - 68 µF, 16V, Solid Tantalum Sprague, “594D series” D1 - 1A, 40V Schottky Rectifier, Surface Mount L1 - 33 µH, L23, Coilcraft DO3316 CB - 0.01 µF, 50V, Ceramic TYPICAL SURFACE MOUNT PC BOARD LAYOUT, ADJUSTABLE OUTPUT (4X SIZE) 01280337 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 - 68 µH, L30, 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. 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. 22 www.national.com LM2675 Application Information (Continued) 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. LLP PACKAGE DEVICES The LM2675 is offered in the 16 lead LLP surface mount package to allow for increased power dissipation compared to the SO-8 and DIP. 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. 23 www.national.com LM2675 Physical Dimensions unless otherwise noted inches (millimeters) 8-Lead (0.150" Wide) Molded Small Outline Package, JEDEC Order Number LM2675M-3.3, LM2675M-5.0, LM2675M-12 or LM2675M-ADJ NS Package Number M08A www.national.com 24 LM2675 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 8-Lead (0.300" Wide) Molded Dual-In-Line Package Order Number LM2675N-3.3, LM2675N-5.0, LM2675N-12 or LM2675N-ADJ NS Package Number N08E 25 www.national.com LM2675 SIMPLE SWITCHER Power Converter High Efficiency 1A Step-Down Voltage Regulator Physical Dimensions inches (millimeters) unless otherwise noted (Continued) 16-Lead LLP Surface Mount Package NS Package Number LDA16A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. BANNED SUBSTANCE COMPLIANCE National Semiconductor manufactures products and uses packing materials that meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. 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