LM34926EVAL/NOPB

User's Guide SNVA675A – August 2012 – Revised April 2013 AN-2284 LM34926 Isolated Evaluation Board 1 Introduction An isolated bias supply is implemented in this evaluation board with LM34926 Constant-On-Time regulator. LM34926 regulator integrates both the high and low side power switches essential for creating isolated buck converter. Board Specifications: • Input Range: 20V to 100V • Primary Output Voltage: 10V • Secondary (Isolated) Output Voltage: 9.5V • Maximum Load Current (Primary + Secondary): 250mA • Maximum Power Output: 2.5W • Nominal Switching Frequency: 750kHz • Efficiency (FIN = 36V, IOUT2 = 250mA): 77 percent • Board size: 2 inch x 2 inch Figure 1. LM34926 Evaluation Board (Top View) All trademarks are the property of their respective owners. SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2284 LM34926 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 1 UVLO Threshold and Hysteresis 2 www.ti.com UVLO Threshold and Hysteresis The UVLO resistors are selected using the following two equations: VIN(HYS) = IHYSR1 (1) and VIN (UVLO,rising) = 1.225V x § R1 · +1 © R2 ¹ (2) On this evaluation board R1 = 127kΩ and R2 = 8.25kΩ, resulting in UVLO rising threshold at VIN = 20.5V and a hysteresis of 2.54V. 2.1 Board Connection and Start-up The input connections are made using TP1 (VIN) and TP2 (GND) terminals. The primary output appears at TP3 (VOUT1) and TP4 (GND). The secondary (isolated) output is available across TP5 (VOUT2) and TP6 (IGND). The input voltage should be gradually increased above UVLO set point of 20.5V. Both the outputs (VOUT1 and VOUT2) should be close to 10V at this point. This board is designed to function with input voltage range of 20V to 100V. The minimum VIN threshold can be changed by changing the UVLO resistors R1, R2. VIN should not exceed 100V. The magnetics in this design is optimized for solution size, and therefore limits the output power. The total load at the output should not exceed 250mA, otherwise the coupled inductor will saturate/overheat, which can destroy both the coupled inductor and the regulator IC U1. If a sustained over-current situation is to be tolerated, a coupled inductor with higher saturation and rms ratings should be used. D1 + C4 1 F R10 2 NŸ VOUT2 9.5V (J3) SW (TP11) T1 IGND BST 2 20V-100V VIN (J1) 4 C1 + 1 F + R3 130 NŸ C5 0.1 F SW VIN 7 8 + 0.01 F C2 R8 RON LM34926 46.4 NŸ 47 H (1:1) 1000 pF R1 127 NŸ 3 VCC UVLO FB (TP7) R2 UVLO 8.25 NŸ EXP RTN 1 6 R4 7.32 NŸ D2 5 + U1 0Ÿ R6 C7 C8 0.1 F + C3 1 F VOUT1 10V (J2) GND R5 1 NŸ C6 1 F Figure 2. Complete Evaluation Board Schematic 2 AN-2284 LM34926 Isolated Evaluation Board SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated Bill of Materials www.ti.com 3 Bill of Materials Table 1. Bill of Materials Item Description Mfg., Part Number Package Value U1 Sync Switching Regulator Texas Instruments, LM34926 WSON-8 100V, 300mA T1 Coupled Inductor, 1500 VDC Coilcraft, LPD5030V-473ME 5mm x 5mm 47uH, 0.47A Alternate Part Wurth, 750312750 8.26mm x 6.60mm 22uH, 0.76A Schottky Diode Diodes Inc., DFLS1100-7 Pwr–DI123 100V, 1A D1 D2 Schottky Diode Diodes Inc., SDM10U45-7 SOD–523 40V, 100mA C1 Ceramic Capacitor MuRata, GRM32CR72A105KA35L 1210 1uF, 100V, X7R C2 Ceramic Capacitor TDK, C1608X7R1C103K 0603 0.01uF, 16V, X7R C3, C4 Ceramic Capacitor TDK, C2012X7R1E105K 0805 1uF, 25V, X7R C5 Ceramic Capacitor Kemet, C0805C104K1RACTU 0805 0.1uF, 100V, X7R C6 Ceramic Capacitor TDK, C1608X7R1C105K 0603 1uF, 16V, X7R C7 Ceramic Capacitor Murata, GRM188R71E102KA01D 0603 1000pF,25V, X7R C8 Ceramic Capacitor AVX, 0603YC104KAT2A 0603 0.1uF, 16V, X7R R1 Resistor Vishay/Dale, CRCW0805127KFKEA 0805 127kΩ, 1% R2 Resistor Vishay/Dale, CRCW08058K25FKEA 0805 8.25kΩ, 1% R3 Resistor Vishay/Dale, CRCW0805130KFKEA 0805 130kΩ, 1% R4 Resistor Panasonic, ERJ-3EKF7321V 0603 7.32kΩ, 1% R5 Resistor Panasonic, ERJ-3EKF1001V 0603 1.0kΩ,1% R6 Resistor Yageo, RC0603JR-070RL 0603 0Ω R8 Resistor Panasonic, ERJ-3EKF4642V 0603 46.4kΩ, 1% R10 Resistor Panasonic, ERJ-6GEYJ202V 0805 2kΩ, 5% SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2284 LM34926 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 3 Performance Curves 4 www.ti.com Performance Curves 100 EFFICIENCY (%) 90 VIN=36V VIN=24V 80 VIN=48V 70 60 VOUT2=10V, IOUT1=0 50 50 100 150 200 250 LOAD CURRENT (mA) 300 Figure 3. Efficiency at 750kHz, VOUT1=10V Figure 4. Steady State Waveform (VIN=48V, IOUT1=0mA, IOUT2= 100mA) Figure 5. Step Load Response (VIN=48V, IOUT1=0, Step Load on IOUT2=80mA-180mA) 4 AN-2284 LM34926 Isolated Evaluation Board SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated PC Board Layout www.ti.com 5 PC Board Layout Figure 6. Board Silkscreen SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2284 LM34926 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 5 PC Board Layout www.ti.com Figure 7. Board Top Layer 6 AN-2284 LM34926 Isolated Evaluation Board SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback Copyright © 2012–2013, Texas Instruments Incorporated PC Board Layout www.ti.com Figure 8. Board Bottom Layer SNVA675A – August 2012 – Revised April 2013 Submit Documentation Feedback AN-2284 LM34926 Isolated Evaluation Board Copyright © 2012–2013, Texas Instruments Incorporated 7 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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