AN-1724| Application Note

LM5015 Isolated Two-Switch DC-DC Regulator Evaluation Board

LM5015 Isolated TwoSwitch DC-DC Regulator Evaluation Board
Introduction
The LM5015 Isolated DC-DC Regulator evaluation board provides a low cost and fully functional DC-DC regulator without employing any discrete power MOSFET. The evaluation board can be configured as either an Isolated Two-Switch Forward DC-DC Regulator, or an Isolated Two-Switch Flyback DC-DC Regulator. The factory default configuration of the evaluation board is forward topology. The forward converter configuration will produce about 2% higher efficiency and lower output ripple voltage than the flyback. Whereas, the Flyback configuration costs slightly less. Suggestion to reconfigure the evaluation board as an Isolated Two-Switch Flyback DC-DC Regulator is provided at the end of this article. For detailed features and technical information of the LM5015 device, refer to the datasheet (www.national.com/ds/DS/ LM5015.pdf). For non-isolated applications, refer to Application Note AN-1725, the LM5015 Non-Isolated Two-Switch

National Semiconductor Application Note 1724 Youhao,Xi October 2007

DC-DC Regulator Evaluation Board (www.national.com/an/ AN/AN1725.pdf). The evaluation board features: Input Voltage: 36V to 72V Isolated Output Voltage: 5V Output Current: 0A minimum, 2.5A nominal, and 3A maximum Input UVLO Threshold: 34V nominal Measured Efficiency: 86% (VIN = 48V, IOUT = 2.5A) Switching Frequency: 300 kHz Ability to Synchronize to External Clock Ability to Be Remote Controlled (Enable/Disable) Two Layer PC Board and Top Side Component Placement Configurable as Either a Forward (Factory Default) or a Flyback Regulator Board Size (WxLxH): 2.5 in. x 3.5 in. x 0.63 in

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FIGURE 1. Evaluation Board Layout

Board Connections/Start-up
Figure 1 shows the PC board layout. The input connections are made to connectors J1 (high potential) and J2 (input return). The load is connected between connectors J3 (5V) and J4 (5V return). Ensure the wires are adequately sized for the intended load current. A DC power supply capable of at least 75V and 0.5A is recommended as the input power source for the evaluation board. Use the output over-voltage and over-current limit fea-

tures of the DC power supply to protect the board against damage by errant connections. A resistive load is optimal, but an appropriate electronic load is acceptable. The maximum load current is 3A. Exceeding this current will cause the LM5015 to enter cycle-by-cycle peak current limit mode, and the output voltage will fall below the regulated 5V. Current limit mode is triggered whenever the primary switch current exceeds 1.2A (nominal). During the first power up, the load should be kept reasonably low, e.g. <0.1A. Before start-up, a voltmeter should be con-

AN-1724

2007 National Semiconductor Corporation

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www.national.com