LM2679-5.0EVAL

User's Guide SNVA013D – December 2000 – Revised April 2013 AN-1135 LM267X 3A, 5A Evaluation Boards 1 Introduction The LM267X evaluation board was developed for the evaluation of LM267X SIMPLE SWITCHER series of 3 Amp and 5 Amp high efficiency step-down (Buck) switching voltage regulators. This application note describes the printed circuit board, and provides example circuits and directions on setup and operation of the LM2673S-5_EVAL and LM2679S-5_EVAL evaluation boards. 2 General Description Many of our boards are intended to provide the user with device characterization and layout optimization data. The LM267x evaluation board was intended to allow the user to experiment with a variety of circuit topologies and components, and therefore not optimized for size. Please refer to the discussions of layout optimization in the PCB Layout Optimization section. This board was designed such that both through-hole and surface-mount components can be used for construction. The regulator IC can be placed on the board as a surface-mount component only. The ground plane serves as a heatsink. Table 1 shows an overview of the family of devices with special features of each indicated. Consult the device data sheet, or use the special power supply design software calledSwitchers Made Simple version 6.X (available for free download from www.ti.com) to determine all necessary component values for the particular device being used to accomplish a specific design and board layout considerations. The printed circuit board, PCB, is labeled to indicate the location of all of the needed components for all possible design options. Table 2 shows a complete list of the component labels and their functions. Figure 1 identifies all components, but not all are necessary in every design. Figure 2, Figure 3 and Figure 4 show the top, bottom and silk screen of the printed circuit board respectively. Table 1. LM267X Family of High-Current Regulators supported by the Evaluation Board Device Maximum Load Current (A) LM2670 3 ON/OFF, External Frequency Sync Capability LM2673 3 Adjustable Current Limit, Softstart LM2676 3 ON/OFF LM2677 5 ON/OFF, External Frequncy Sync. Capability LM2678 5 ON/OFF LM2679 5 Adjustable Current Limit, Softstart SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Special Features AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 1 General Description www.ti.com Figure 1. Example Schematic Showing Connection for all Components. Table 2. List of Component Labels and Functionality Label U1 LM267 Switching Regulator IC CIN Input Capacitor(s); All devices. CINX 0.47 µF, optional high frequency input bypass capacitor, recommended in all designs: All devices. CB Boost capacitor; All devices. D1 Catch diode; All devices. R1 Feedback resistor for adjustable output converters. This designator is left open (not connected) for fixed output converters. R2 Feedback resistor (typ. 1 kΩ) for adjustable output converters. This designator is left shorted (replaced by a jumper wire) for fixed output voltage converters. R3* Current limit resistor for LM2673, LM2679; Sync input resistor (1 kΩ) for LM2670 and LM2677; Not inserted for LM2676 and LM2678. L1 Inductor; All devices. CSYNC CSS COUTX COUT 2 Function Sync input capacitor (100 pF); LM2670 and LM2677only. Not inserted with other devices. Soft start capacitor; LM2673 and LM2679 only. Not inserted with other devices. 0.47 µF, optional high frequency output bypass capacitor; All devices. Output capacitor(s); All devices. AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated General Description www.ti.com Figure 2. Top Layer Foil Pattern of Printed Circuit Board Figure 3. Bottom Layer Foil Pattern of Printed Circuit Board SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 3 Special Notes www.ti.com Figure 4. Silkscreen Image of Printed Circuit Board 3 Special Notes The evaluation board was designed primarily for circuit implementation using all surface-mount components. The small series "trace inductance", particularly from the Switch Output pin, can create a high frequency (10's of MHz) ringing signal at the switch output. If problematic, this ringing can be reduced or eliminated by the use of a series RC damper or snubber network from the switch output to ground. The addition of these components is made at the locations labeled CD and RD. Values of 0.01 µF and 10Ω are good starting values that may need to be varied depending on the magnitude of parasitic factors in a given design. In an actual end application, these components are normally not required if proper care to minimize trace lengths is taken in the PCB design. 4 Example Circuit Designs Example 1: 5V/3A Converter with Surface Mount Components. In this example, it is desired to convert a voltage range of between 8V and 12V, to 5VDC with load current of 3A. It is also desired to implement the design with surface mount components only. Softstart duration will be set to between 1 and 1.5 ms. Table 3. Target Design Specifications VIN min. 8V VIN max. 16V VOUT 5V ILOAD 3A ICL 5.0A (approx.) TSS 1 to 1.5 ms Table 4. Component Values for an 8-12V in, 5V/3A Out LM2673S-5.0 Buck Converter Component Value Suggested Part Number U1 4 Texas Instruments LM2673 CIN 2 x 33 µF/35V Vishay 594D336X0035R2T CINX 0.47 µF Vishay VJ1210U474ZXAA AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated Example Circuit Designs www.ti.com Table 4. Component Values for an 8-12V in, 5V/3A Out LM2673S-5.0 Buck Converter (continued) Component Value Suggested Part Number CB 0.01 µF/50V Vishay VJ1206Y103MXXA D1 3A/60V Schottky (450 mV at 3A) Motorola MBRD360 R3* 7.15 kΩ (5.19A current limit) Vishay CRCW12067151J L1 22 µH (L41) SUMIDA ELECTRIC CO. CDRH127-220 Vishay VJ1206Y33ZJXBAB CSS 3.3 nF/100V (softstart) COUTX 0.47 µF Vishay VJ1210U474ZXAA COUT 2 x 18 0µF/16V Vishay 594D187X0016R2T Figure 5 below shows the 5V/3A design circuit. This solution is available as evaluation board LM2673S5_EVAL. Figure 6 through Figure 9 show the output waveforms for output voltage with 500 mA load, output voltage with 1A load, output ripple with 1A load, output voltage with 3A load, output ripple with 3A load, output response to 1A transient load and output response to 3A transient load respectively. Figure 5. 5V/3A Design Circuit A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 500 mA; 500 mA/DIV Figure 6. Output Voltage with 500 mA Load SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 5 Example Circuit Designs www.ti.com A: OUTPUT RIPPLE; 10 mV/DIV B: LOAD CURRENT: ILOAD = 0.5A; 1A/DIV Figure 7. Output Ripple with 500 mA Load A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 1A; 500 mA/DIV Figure 8. Output Voltage with 1A Load A: OUTPUT RIPPLE; 10 mV/DIV B: LOAD CURRENT: ILOAD = 1A; 1A/DIV Figure 9. Output Ripple with 1 Amp Load 6 AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated Example Circuit Designs www.ti.com A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 3A; 1A/DIV Figure 10. Output Voltage with 3A Load A: OUTPUT RIPPLE; 10 mV/DIV B: LOAD CURRENT: ILOAD = 3A; 1A/DIV Figure 11. Output Ripple with 3 Amp Load A: OUTPUT RESPONSE; 1V/DIV B: TRANSIENT LOAD CURRENT: 1A/DIV Figure 12. Output Response to 0∼ ∼1A Transient Load SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 7 Example 2: 5V/5A Design with Surface Mount Components www.ti.com A: OUTPUT RESPONSE; 1V/DIV B: TRANSIENT LOAD CURRENT: 2A/DIV Figure 13. Output Response to 0∼ ∼3A Load Transient 5 Example 2: 5V/5A Design with Surface Mount Components For this example, it is desired to design a power supply to convert an input voltage within the range of 14V and 28V to an output voltage of 5V with a maximum load current of 5A using only surface mount components. In addition, the current limit of the regulator will be set to approximately 7.0A, and the softstart time will be set to approximately 1.0 ms to limit the startup surge current. Table 5. Target Design Specifications: VIN min. 14V VINmax. 28V VOUT 5V ILOAD 5A ICL 7.0A (approx.) TSS 1.0 ms (approx.) Table 6. Component Values for an 14V-28V in, 5V/5A Out LM2679S-5.0 Buck Converter Component Value Suggested Part Number U1 Texas Instruments LM2679 CIN 3 x 15 µF/50V Vishay 594D156X0050R2T CINX 0.47µF Vishay VJ1210U474ZXAA CB 0.01µF/50V Vishay VJ1206Y103ZXXA D1 8A/35V Schottky (500 mV at 5A) Motorola MBRD835L R3* 4.99 kΩ (7.19A current limit) Vishay CRCW12064991J L1 15 µH Coilcraft D05022P-153 Vishay VJ1206Y47ZJXBAB CSS 4.7 nF/100V (1.0 ms softstart) COUTX 0.47 µF Vishay VJ1210U474ZXAA COUT 2 x 180 µF/16V Vishay 594D187X0016R2T Figure 14 below shows the circuit for the 5V/5A design. This solution is available as evaluation board LM2679S-5_EVAL. Figure 14 through Figure 23 show the output waveforms for output voltage with 500 mA load, output voltage with 2.5A load, output ripple with 2.5A load, output voltage with 5A load, output ripple with 5A load, output response to 500 mA transient load, output response to 2.5A transient load and output response to 5A transient load respectively. 8 AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated Example 2: 5V/5A Design with Surface Mount Components www.ti.com Figure 14. 5V/5A Design Circuit A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 500 mA; 500 mA/DIV Figure 15. Output Voltage with 500 mA Load A: OUTPUT RIPPLE; 100 mV/DIV B: LOAD CURRENT: ILOAD = 500 mA; 1A/DIV Figure 16. Output Ripple with 500 mA Load SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 9 Example 2: 5V/5A Design with Surface Mount Components www.ti.com A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 2.5A; 1A/DIV Figure 17. Output Voltage with 2.5A Load A: OUTPUT RIPPLE; 100 mV/DIV B: LOAD CURRENT: ILOAD = 2.5A; 2A/DIV Figure 18. Output Ripple with 2.5A Load A: OUTPUT VOLTAGE: VOUT; 2V/DIV B: LOAD CURRENT: ILOAD = 5A; 2A/DIV Figure 19. Output Voltage with 5A Load 10 AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated Example 2: 5V/5A Design with Surface Mount Components www.ti.com A: OUTPUT RIPPLE; 100 mV/DIV B: LOAD CURRENT: ILOAD = 5A; 5A/DIV Figure 20. Output Ripple with 5A Load A: OUTPUT RESPONSE; 1V/DIV B: TRANSIENT LOAD CURRENT: 500 mA/DIV Figure 21. Output Response to 0∼ ∼0.5A Transient Load A: OUTPUT RESPONSE; 1V/DIV B: TRANSIENT LOAD CURRENT: 1A/DIV Figure 22. Output Response to 0∼ ∼2.5A Load Transient SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback AN-1135 LM267X 3A, 5A Evaluation Boards Copyright © 2000–2013, Texas Instruments Incorporated 11 Operating the Evaluation Boards www.ti.com A: OUTPUT RESPONSE: 1V/DIV B: LOAD CURRENT: ILOAD = 1A/DIV Figure 23. Output Response to 0∼ ∼5A Transient Load 6 Operating the Evaluation Boards 6.1 Setup The LM2673S-5_EVAL and LM2679S-5_EVAL evaluation boards come ready to be tested. The only setup needed is connecting the input voltage to the VIN and GND posts. The output can be taken from the VOUT post. The other signals of interest, switch output (SW out) and softstart (C_SS) posts, are clearly marked for use in checking the signal integrity. The softstart post has an ON/OFF input when this feature is being used. 6.2 Operating Conditions The input source for the LM267x family of regulators must be 8V or greater for proper setup and operation. The input voltage range for LM2673S-5_EVAL evaluation board is from 8V to 12V and the range for LM2679S-5_EVAL is from 14V to 28V. The maximum voltage rating of the LM267x family of regulators is 40V. Load can be applied from 0A to the maximum for the design. Higher current above the design current limit will result in activation of the design current limit circuit. It is advisable to have a minimal load of (at least 10 mA) during startup when the input to output differential voltage is greater than 10V to prevent output ramping beyond desired value. 6.3 PCB Layout Optimization As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the printed circuit traces should be as wide and short as possible on the PCB. 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 groundpath 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 associated wiring. Physically locate both resistors near the IC, and route the wiring away from the inductor, especially an open core type of inductor. 12 AN-1135 LM267X 3A, 5A Evaluation Boards SNVA013D – December 2000 – Revised April 2013 Submit Documentation Feedback Copyright © 2000–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. 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