AN-1577| Application Note
LM25574 Evaluation Board
LM25574 Evaluation Board
National Semiconductor Application Note 1577 Robert Bell January 2007
Introduction
The LM25574 evaluation board is designed to provide the design engineer with a fully functional power converter based on Emulated Current Mode Control to evaluate the LM25574 regulator IC. The evaluation board provides a 5V output with a 0.5A current capability. The ultra-wide input voltage ranges from 7V to 42V. The design operates at 300kHz, a good compromise between conversion efficiency and solution size. The printed circuit board consists of 2 layers of 2 ounce copper on FR4 material with a thickness of 0.06 inches. This application note contains the evaluation board schematic, Bill-of-Materials (BOM) and a quick setup procedure. Refer to the LM25574 datasheet for complete circuit design information. The performance of the evaluation board is as follows: Input Range: 7 to 42V Output Voltage: 5V Output Current: 0 to 0.5A Frequency of Operation: 300 KHz Board Size: 2.1 X 1 X 0.4 inches Load Regulation: 1% Line Regulation: 0.1% Over Current Limiting
Evaluation Board Schematic
30006901
Powering and Loading Considerations
Read this entire page prior to attempting to power the evaluation board. QUICK SETUP PROCEDURE Step 1: Set the power supply current limit to 0.6A. Turn off the power supply. Connect the power supply to the Vin terminals. Step 2: Connect the load, with a 0.5A capability, to the Vout terminals. Positive connection to J2 and negative connection to J3. Step 3: The SD pin should be left open for normal operation. Step 4: Set Vin to 24V with no load applied. Vout should be in regulation with a nominal 5V output.
2007 National Semiconductor Corporation 300069
Step 5: Slowly increase the load while monitoring the output voltage, Vout should remain in regulation with a nominal 5V output as the load is increased up to 0.5 Amps. Step 6: Slowly sweep the input voltage from 7 to 42V, Vout should remain in regulation with a nominal 5V output. Step 7: Temporally short the SD pin to GND to check the shutdown function. Step 8: Increase the load beyond the normal range to check current limiting. The output current should limit at approximately 0.7A. The power supply (Vin source) current limit may need to be increased for this step. Cooling is critical during this step. AIR FLOW Prolonged operation with high input voltage at full power will cause the thermal shutdown circuit within the regulator IC to
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AN-1577
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