LM2727EVAL

www.ti.com Table of Contents User’s Guide LM2727 Buck Controller Evaluation Module User's Guide Table of Contents 1 Introduction.............................................................................................................................................................................2 2 Boot Voltage............................................................................................................................................................................ 2 3 Dual MOSFET Footprints....................................................................................................................................................... 2 4 Low-Side Diode.......................................................................................................................................................................2 5 Additional Footprints..............................................................................................................................................................2 6 Layout Optimization............................................................................................................................................................... 3 7 PCB Layout..............................................................................................................................................................................5 8 Revision History......................................................................................................................................................................6 Trademarks All trademarks are the property of their respective owners. SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 LM2727 Buck Controller Evaluation Module User's Guide Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated 1 Introduction www.ti.com 1 Introduction The LM2727 evaluation board has been designed for a wide variety of components in order to show the flexibility of the LM2727 chips. The input voltage limitations are the same as the chip: 2.2 VDC to 16 VDC. The regulated output voltage range is from 0.6 V up to 85% of the input voltage. Output current is limited by the components chosen, however, the size of this board and the limitation to SOIC-8 MOSFETs means a realistic limit of about 10 A. The example design steps 12 V down to 3.3 V at 4 A, with a switching frequency of 800 kHz. This design can be modified by following the Design Considerations section of the LM2727/LM2737 N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages data sheet. The board is four layers, consisting of signal/power traces on top and bottom, with one internal ground plane and an internal split power plane. All planes are 1-oz. copper, and the board is 62-mil FR4 laminate. 2 Boot Voltage The default circuit that comes with the LM2727 demo board uses a bootstrap diode and small capacitor (D1 and CBOOT) to provide enough gate-to-source voltage on the high-side MOSFET to drive the FET. If a separate rail is available that is more than twice the value of VIN, this higher voltage can be connected directly to the BOOT pin, through the BOOT connector, with a 0.1-µF bypass capacitor, CC. In this case, D1 and CBOOT should be removed from the board. Do not connect both CC and CBOOT/D1 at the same time. 3 Dual MOSFET Footprints The LM2727 demo board has two extra footprints for dual N-channel MOSFETs in SOIC-8 packages. Footprint Q3 corresponds to devices with footprints such as the Si4816DY "LITTLEFOOT Plus" from Vishay Siliconix. Footprint Q4 corresponds to devices with footprints such as the Si4826DY, also from Vishay Siliconix. 4 Low-Side Diode A footprint D2 is available for a Schottky diode to be placed in parallel with the low-side FET. This can improve efficiency because a discrete Schottky will have a lower forward voltage than the bodu diode of the low-side FET. The footprint fits SMA size devices. If desired, the low side FET can be removed entirely, and the LM2727 will run as an asynchronous buck controller. 5 Additional Footprints The 1206 footprints Rc2 and Cc3 are available for designs with more complex compensation needs. SOIC-8 Figure 5-1. Pinout for Dual FET for Footprint Q3 SOIC-8 Figure 5-2. Pinout for Dual FET for Footprint Q4 2 LM2727 Buck Controller Evaluation Module User's Guide SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated www.ti.com Layout Optimization 6 Layout Optimization The LM2727 PCB layout could be improved with several techniques used in switching converter design. The traces that run from the HG and LG pins of the IC to the gates of the high-side and low-side MOSFETs should be shorter and thicker, reducing their parasitic inductance and resistance. The mid-frequency decoupling capacitor, CINX, should be placed as close to the pins of the high-side MOSFET as possible. The bulk input capacitors, CIN1 and CIN2, should also be placed close, keeping the loop between the input capacitors and the high-side MOSFET small. Likewise, the Schottky diode D2 should be located as close as possible to the pins of the low-side MOSFET. The local capacitors CIN, CBOOT, and CC (if used) should be close to the pins of the LM2727 IC. These techniques help reduce parasitic inductance throughout the PCB. Figure 6-1. Circuit Schematic SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 LM2727 Buck Controller Evaluation Module User's Guide Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated 3 Layout Optimization www.ti.com Table 6-1. Bill of Materials for Typical Application Circuit 4 ID Part Number Type U1 LM2727 Q1 Si4884DY N-MOSFET SOIC-8 Q2 Si4884DY N-MOSFET SOIC-8 Synchronous Controller Schottky Diode Size Parameters Qty. Vendor 1 NSC 13.5 mΩ, at 4.5 V, 15.3 nC 1 Vishay 13.5 mΩ, at 4.5 V, 15.3 nC 1 Vishay TSSOP-14 Db BAT-54 SOT-23 30 V 1 ON Lin P1168.162T Inductor 12 × 12 × 4.5 mm 1.6 µH, 8.5 A, 5.4 mΩ 1 Pulse Inductor 12 × 12 × 4.5 mm 1.6 µH, 8.5 A, 5.4 mΩ 1 Pulse 1812 10 µF, 25 V, 3.3 Arms 2 TDK L1 P1168.162T Cin1 C4532X5R1E106M Capacitor Cinx C3216X7R1E105K Capacitor 1206 1 µF, 25 V 1 TDK Co1 6TPB470M Capacitor 7.3 × 4.3 × 3.8 mm 470 µF, 2.5 V, 55 mΩ 2 Sanyo Cin C3216X7R1E225K Capacitor 1206 2.2 µF, 25 V 1 TDK Css VJ1206X123KXX Capacitor 1206 12 nF, 25 V 1 Vishay Cc1 VJ1206A3R9KXX Capacitor 1206 3.9 pF, 10% 1 Vishay Cc2 VJ1206A391KXX Capacitor 1206 390 pF, 10% 1 Vishay Rin CRCW1206100J Resistor 1206 10 Ω, 5% 1 Vishay Rfadj CRCW12063052F Resistor 1206 30.5 kΩ, 1% 1 Vishay Rc1 CRCW12069532F Resistor 1206 95.3 kΩ, 1% 1 Vishay Rfb1 CRCW12064871F Resistor 1206 4.87 kΩ, 1% 1 Vishay Rfb2 CRCW12062181F Resistor 1206 21.8 kΩ, 1% 1 Vishay Rcs CRCW1206272J Resistor 1206 2.7 kΩ, 5% 1 Vishay LM2727 Buck Controller Evaluation Module User's Guide SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated www.ti.com PCB Layout 7 PCB Layout Figure 7-1. PCB Top Layer and Top Overlay Figure 7-2. PCB Bottom Layer and Internal Power Plane SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 LM2727 Buck Controller Evaluation Module User's Guide Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated 5 Revision History www.ti.com Figure 7-3. PCB Overall 8 Revision History NOTE: Page numbers for previous revisions may differ from page numbers in the current version. Changes from Revision C (April 2013) to Revision D (February 2022) Page • Updated the numbering format for tables, figures, and cross-references throughout the document. ................2 • Updated the user's guide title............................................................................................................................. 2 6 LM2727 Buck Controller Evaluation Module User's Guide SNVA057D – AUGUST 2002 – REVISED FEBRUARY 2022 Submit Document Feedback Copyright © 2022 Texas Instruments Incorporated IMPORTANT NOTICE AND DISCLAIMER TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCE DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS” AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD PARTY INTELLECTUAL PROPERTY RIGHTS. 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