LM5018EVAL/NOPB

User's Guide SNVA666A – June 2012 – Revised April 2013 AN-2237 LM5018 Buck Evaluation Board 1 Introduction The LM5018 evaluation board, Figure 1, provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 10V output over an input range of 12.5V to 100V. The board’s specifications are: • Input Range: 12.5V to 95V, transients up to 100V (absolute maximum) • Output Voltage: 10V • Output Current: 300 mA • Nominal Switching Frequency ~ 440 kHz • Measured Efficiency: 88.4% at 300mA and VIN = 24V • Board size: 5.5 cm × 4.5 cm Figure 1. Evaluation Board (Top View) All trademarks are the property of their respective owners. SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 1 Theory of Operation 2 www.ti.com Theory of Operation Refer to the evaluation board schematic in Figure 2. When the circuit is in regulation, the buck switch is turned on each cycle for a time determined by R3 and VIN according to the equation: TON = 10 -10 x R3 VIN (1) The on-time of this evaluation board ranges from 5.56µs at VIN = 12V to 702ns at VIN = 95V. The on-time varies inversely with input voltage. At the end of each on-time the buck switch is off for at least 144ns. In normal operation, the off-time is much longer. During the off-time, the load current is supplied by the output capacitor (C9). When the output voltage falls sufficiently that the voltage at FB is below 1.225V, the regulation comparator initiates a new on-time period. For stable, fixed frequency operation, a minimum of 25mV of ripple is required at FB to switch the regulation comparator. For a more detailed block diagram and a complete description of the various functional blocks, see LM5018 100V, 300mA Constant On-Time Synchronous Buck Regulator (SNVS787). SW 12V - 95V VIN (TP1) LM5018 2 C4 1 F + R3 C5 + R5 0.1 F 127 NŸ 237 NŸ GND (TP2) UVLO/SD 4 3 BST VIN SW RON 7 0.01 F + C1 8 L1 VOUT 220 H UVLO VCC R7 14 NŸ FB EXP RTN 1 R1 6.98 NŸ 6 + U1 C8 0.1 F + D2 5 C7 1 F R6 (TP3) R2 1.5Ÿ 1 NŸ C9 4.7 F GND (TP5) Figure 2. Complete Evaluation Board Schematic for LM5018 Based Buck Converter 3 UVLO The UVLO resistors (R5, R7) are selected using the following two equations: VIN(HYS) = IHYSR5 (2) and VIN (UVLO,rising) = 1.225V x § R5 © R7 +1· ¹ (3) On this evaluation board R5=127kΩ and R7=14.0kΩ, resulting in UVLO rising threshold at VIN=12V and a hysteresis of 2.5V. 4 Board Connection and Start-up The input connections are made to the TP1 (VIN) and TP2 (GND) terminals. The load is connected to the TP3 (VOUT) AND TP5 (GND) terminals. Ensure the wires are adequately sized for the intended load current. Before start-up a voltmeter should be connected to the input terminals, and to the output terminals. The load current should be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased gradually to 12V, at which time the output voltage should be 10V. If the output voltage is correct, then increase the input voltage as desired and proceed with evaluating the circuit. DO NOT EXCEED 100V AT VIN. Caution: Do not leave EVM powered when unattended. 2 AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback Bill of Materials www.ti.com 5 Bill of Materials Item Description Mfg., Part Number Package Value C5 Ceramic Capacitor Kemet, C0805C104K1RACTU 0805 0.1uF, 100V, X7R C7 Ceramic Capacitor TDK, C2012X7R1C105K 0805 1uF, 16V, X7R C8 Ceramic Capacitor Murata, GRM188R71E104KA01D 0603 0.1uF, 25V, X7R, 0603 C9 Ceramic Capacitor Murata, GRM21BR61E475KA12L 0805 4.7uF, 25V, X5R Diode Diodes, Inc., SDM10U45–7–F SOD-523 Schottky, 45V, 0.1A Inductor Cooper Bussman, DR74–221–R 7.6mm × 7.6mm 220uH, 0.66A 220uH, 0.54A D2 L1 6 Alternate Inductor Wurth, 744777222 7.3mm x 4.5mm R1 Resistor Vishay-Dale, CRCW08056K98FKEA 0805 220uH, 0.6A R2 Resistor Vishay-Dale, CRCW08051R50FKEA 0805 1.50 ohm, 1%, 0.125W R3 Resistor Vishay-Dale, CRCW0805237KFKEA 0805 237k ohm, 1%, 0.125W R5 Resistor Vishay-Dale, CRCW0805127KFKEA 0805 127k ohm, 1%, 0.125W R6 Resistor Vishay-Dale, CRCW08051K00FKEA 0805 1.00k ohm, 1%, 0.125W R7 Resistor Vishay-Dale, CRCW080514K0FKEA 0805 14.0k ohm, 1%, 0.125W U1 Sync Switching Regulator Texas Instruments, LM5018 SO PowerPAD-8 100V, 0.3A Ripple Configuration The LM5018 is a constant-on-time (COT) buck, and requires adequate ripple at feedback (FB) node. Three commonly used ripple generation methods are shown in Table 1. The LM5018 evaluation board has been supplied with reduced ripple configuration (Type 2). For more information on ripple configuration, see LM5018 100V, 300mA Constant On-Time Synchronous Buck Regulator (SNVS787). Table 1. Ripple Configurations Type 1: Lowest Cost Configuration Type 2: Reduced Ripple Configuration Type 3: Minimum Ripple Configuration VOUT VOUT L1 VOUT L1 L1 Cac R FB2 R FB2 RC To FB C OUT R FB1 R FB2 C OUT GND C OUT To FB R FB1 GND GND C8 open. Select R2: 40 mV VOUT x ûIL(MIN) VREF Cr Cac To FB R FB1 R2 > Rr RC Select R2 and C8: (4) 5 C8 > gSW (R1 || R6) 40 mV R2 > ûIL (Not on Board) Cr = 3300 pF Cac = 100 nF (VIN(MIN) ± VOUT)TON Rr x Cr < 40 mV (5) (6) SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 3 Performance Curves 7 www.ti.com Performance Curves Figure 3. Efficiency vs Load Current Figure 4. Frequency vs Input Voltage Figure 5. Typical Switching Waveform (VIN = 48V, Iout = 200mA) 4 AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback PC Board Layout www.ti.com 8 PC Board Layout Figure 6. Board Silkscreen SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 5 PC Board Layout www.ti.com Figure 7. Board Top Layer Figure 8. Board Bottom Layer 6 AN-2237 LM5018 Buck Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated SNVA666A – June 2012 – Revised April 2013 Submit Documentation Feedback 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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