LM3679TL-1.8EV

User's Guide SNVA270C – October 2007 – Revised April 2013 AN-1682 LM3679TL Evaluation Board 1 Introduction The LM3679TL evaluation board is a working demonstration of a step down DC-DC converter. This application report contains information about the evaluation board. For further information on buck converter topology, device electrical characteristics, and component selection, see the device-specific data sheet. 2 General Description The LM3679TL, a high efficient step down DC-DC switching buck converter, steps down a constant voltage for cell phones, PDA’s, and many other applications from a single Li-ion battery ranging from 2.5 V to 5.5 V. The automatic intelligent switching between PFM and PWM provides high efficiency throughout the IOUT range. The LM3679 is available in a 1.8 V output voltage option in a 5-bump DSBGA and ultra thin UR package*. Using the UR package along with specific external components, allows for a low profile solution size with a max height of 0.55 mm. A switching frequency of 3 MHz (typ.) permits use of miniature surface mount external components. NOTE: Contact Texas Instruments for the UR samples. 3 Operating Conditions • • • • 4 VIN range: 2.5 V ≤ VIN ≤ 5.5 V Recommended load current: 0 mA ≤ IOUT ≤ 350 mA Ambient temperature (TA) range: -30°C to +85°C Junction temperature (TJ) range: -30°C to +125°C Typical Application VIN 2.5V to 5.5V L1: 1.0 PH VIN 1 CIN 4.7 PF GND 5 VOUT SW COUT 10 PF LM3679 2 EN 3 4 FB Figure 1. Typical Application Circuit All trademarks are the property of their respective owners. SNVA270C – October 2007 – Revised April 2013 Submit Documentation Feedback AN-1682 LM3679TL Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 1 Connection Diagram and Package Mark Information 5 www.ti.com Connection Diagram and Package Mark Information VIN A1 A3 B2 EN C3 C1 GND GND SW SW FB FB Top View A3 A1 VIN C1 EN B2 C3 Bottom View Figure 2. 5-Bump DSBGA and YPD Package 6 7 Pin Descriptions Pin No Name Description A1 VIN Power supply input. Connect to the input filter capacitor (see Figure 1) A3 GND Ground pin C1 EN Enable input. The device is in shutdown mode when voltage to this pin is 1.0 V. Do not leave this pin floating. C3 FB Feedback analog input. Connect directly to the output filter capacitor for fixed voltage versions. B2 SW Switching node connection to the internal PFET switch and NFET synchronous rectifier. Powering the LM3679 for Bench Measurement When powering the LM3679 with a bench power supply, it is recommended to place a 100 µF tantalum capacitor across the VIN and GND supply terminals of the bench power supply. This capacitor reduces the input spike caused by the power supply and long power cables. The combination of the power supply and inductance within the power cables produce a large voltage spike that may damage the device. In addition, consideration must be given to the enable pin of the device. The enable should never be taken high, until minimum specified operating voltage of 2.7 V is reached. The enable pin should also never exceed the input voltage. 8 Evaluation Board Layout PC board layout is an important part of DC-DC converter design. Poor board layout can disrupt the performance of a DC-DC converter and surrounding circuitry by contributing to EMI, ground bounce, and resistive voltage loss in the traces. These can send erroneous signals to the DC-DC converter IC, resulting in poor regulation or instability. Poor layout can also result in re-flow problems leading to poor solder joints between the DSBGA/YPD package and board pads. These poor solder joints can result in erratic or degraded performance. 2 AN-1682 LM3679TL Evaluation Board SNVA270C – October 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Evaluation Board Layout www.ti.com Figure 3. Top Layer (5-bump DSBGA/YPD) Figure 4. Bottom Layer (5-bump DSBGA/YPD) SNVA270C – October 2007 – Revised April 2013 Submit Documentation Feedback AN-1682 LM3679TL Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 3 Evaluation Board Layout 8.1 www.ti.com Board Layout Considerations 1. Place the LM3679 on 10.82 mil pads. As a thermal relief, connect to each pad with a 7 mil wide, approximately 7 mil long trace, and then incrementally increase each trace to its optimal width. The important criterion is symmetry to ensure the solder bumps on the re-flow evenly (see DSBGA Package Assembly and Use). 2. Place the LM3679, inductor and filter capacitors close together and make the traces short. The traces between these components carry relatively high switching currents and act as antennas. Following this rule reduces radiated noise. Special care must be given to place the input filter capacitor very close to the VIN and GND pin. 3. Arrange the components so that the switching current loops curl in the same direction. During the first half of each cycle, current flows from the input filter capacitor, through the LM3679 and inductor to the output filter capacitor and back through ground, forming a current loop. In the second half of each cycle, current is pulled up from ground, through the LM3679 by the inductor, to the output filter capacitor and then back through ground, forming a second current loop. Routing these loops so the current curls in the same direction prevents magnetic field reversal between the two half-cycles and reduces radiated noise. 4. Connect the ground pins of the LM3679, and filter capacitors together using generous component-side copper fill as a pseudo-ground plane. Then connect this to the ground-plane (if one is used) with several vias. This reduces ground-plane noise by preventing the switching currents from circulating through the ground plane. It also reduces ground bounce at the LM3679 by giving it a low-impedance ground connection. 5. Use wide traces between the power components and for power connections to the DC-DC converter circuit. This reduces voltage errors caused by resistive losses across the traces 6. Route noise sensitive traces such as the voltage feedback path away from noisy traces between the power components. The voltage feedback trace must remain close to the LM3679 circuit and should be routed directly from FB to VOUT at the output capacitor and should be routed opposite to noise components. This reduces EMI radiated onto the DC-DC converter’s own voltage feedback trace. 7. Place noise sensitive circuitry, such as radio IF blocks, away from the DC-DC converter, CMOS digital blocks and other noisy circuitry. Interference with noise-sensitive circuitry in the system can be reduced through distance. In mobile phones, for example, a common practice is to place the DC-DC converter on one corner of the board, arrange the CMOS digital circuitry around it (since this also generates noise), and then place sensitive pre-amplifiers and IF stages on the diagonally opposing corner. Often, the sensitive circuitry is shielded with a metal pan and power to it is post-regulated to reduce conducted noise, using low-dropout linear regulators. 4 AN-1682 LM3679TL Evaluation Board SNVA270C – October 2007 – Revised April 2013 Submit Documentation Feedback Copyright © 2007–2013, Texas Instruments Incorporated Bill of Materials (BOM) For Common Configurations www.ti.com 9 Bill of Materials (BOM) For Common Configurations Table 1. Bill of Materials (BOM) For Common Configurations Manufacture Manufacture No Description LM3679 - 1.8 V FIXED C1 (input C) TDK C1608X5R0J475 4.7 µF, 6.3 V, 0603, 10% C2 (output C) TDK C1608X5R0J106 10 µF, 6.3 V, 0603, 10% L1 (inductor) FDK MIPSA2520D 1.0 µH inductor, DCR = 100mΩ R1 (VOUT to VFB ) Vishay CRCW06030R00F 0 Ω, 0603, 1% R2 (VFB to GND) None C3 (VOUT to VFB ) None C4 (VFB to GND) None LM3679 - 1.8 V FIXED (Low Profile Application, 0.55 max height) (1) C1 (input C) Taiyo-Yuden JMK107BJ475K 4.7 µF, 6.3 V, 0603, (0.5 mm height) C2 (output C) Taiyo-Yuden JMK107BJ475K 4.7 µF, 6.3 V, 0603, (0.5 mm height) X 2 L1 (inductor) Murata LQM21PN1R0M 1.0 µH inductor, (0.55 mm max height) R1 (VOUT to VFB ) None R2 (VFB to GND) None C3 (VOUT to VFB ) None C4 (VFB to GND) None COMMON TO ALL VIN banana jack - red Johnson Components 108-0902-001 Connector, insulated banana jack (red) VOUT banana jack - yellow Johnson Components 108-0907-001 Connector, insulated banana jack (yellow) GND banana jack - black Johnson Components 108-0903-001 Connector, insulated banana jack (black) Post for EN Turrent 1573-2 Upright post from eval board Post for VIN Turrent 1502-2 Upright post from eval board Post for VOUT Turrent 1502-2 Upright post from eval board Post for GND Turrent 1502-2 Upright post from eval board (1) Contact Texas Instruments for the UR samples. SNVA270C – October 2007 – Revised April 2013 Submit Documentation Feedback AN-1682 LM3679TL Evaluation Board Copyright © 2007–2013, Texas Instruments Incorporated 5 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. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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