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User's Guide

SNVA676A–August 2012–Revised April 2013

AN-2285 LM34925 Isolated Evaluation Board

1 Introduction

An isolated bias supply is implemented in this evaluation board with LM34925 Constant-On-Time

regulator. The LM34925 regulator integrates both the high and low side power switches essential for

creating isolated buck converter.

The following include the board specifications:

• Input Range: 20V to 100V

• Primary Output Voltage: 10V

• Secondary (Isolated) Output Voltage: 9.5V

• Maximum Load Current (Primary + Secondary): 100mA

• Maximum Power Output: 1W

• Nominal Switching Frequency: 750kHz

• Efficiency (FIN = 24V, IOUT2 = 100mA): 70%

• Board size: 2 inch x 2 inch

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SNVA676A–August 2012–Revised April 2013 AN-2285 LM34925 Isolated Evaluation Board

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Summary of content (9 pages)

PAGE 1
User's Guide SNVA676A – August 2012 – Revised April 2013 AN-2285 LM34925 Isolated Evaluation Board 1 Introduction An isolated bias supply is implemented in this evaluation board with LM34925 Constant-On-Time regulator. The LM34925 regulator integrates both the high and low side power switches essential for creating isolated buck converter. The following include the board specifications: • Input Range: 20V to 100V • Primary Output Voltage: 10V • Secondary (Isolated) Output Voltage: 9.
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UVLO Threshold and Hysteresis www.ti.com Figure 1. LM34925 Evaluation Board (Top View) 2 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.
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UVLO Threshold and Hysteresis www.ti.com 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.
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Bill of Materials 3 www.ti.com Bill of Materials Table 1. Bill of Materials 4 Item Description Mfg., Part Number Package Value U1 Sync Switching Regulator Texas Instruments, LM34925 WSON-8 100V, 100mA T1 Coupled Inductor, 1500 VDC Coilcraft, LPD5030V-154ME 5mm x 5mm 150uH, 0.47A D1 Schottky Diode Diodes Inc., DFLS1100-7 Pwr–DI123 100V, 1A D2 Schottky Diode Diodes Inc., SDM10U45-7 SOD–523 40V, 100mA C1 Ceramic Capacitor MuRata, GRM32CR72A105KA35L 1210 1uF, 100V, X7R 0.
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Performance Curves www.ti.com 4 Performance Curves 100 EFFICIENCY (%) 90 80 VIN=24V VIN=36V 70 60 VIN=48V 50 40 30 VOUT2=10V, IOUT1=0 20 30 40 50 60 70 80 90 100 110 LOAD CURRENT (mA) Figure 3. Efficiency at 750kHz, VOUT1=10V Figure 4.
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PC Board Layout 5 www.ti.com PC Board Layout Figure 5.
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PC Board Layout www.ti.com Figure 6.
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PC Board Layout www.ti.com Figure 7.
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