AN-1529| Application Note

LM3430 Evaluation Board

National Semiconductor Application Note 1529 Chris Richardson January 2007

Specifications Of The Board
The Evaluation Board has been designed for testing of various circuits using the LM3430 boost regulator controller. A complete schematic for all the components is shown in Figure 3. The board is two layers with components and power paths in 1oz. copper. The board is 62mil FR4 laminate.

Testing The Converter
Figure 4 shows a block diagram of connections for making measurements of efficiency. The wires used for making connections at both the input and output should be rated to at least 10A of continuous current and should be no longer than is needed for convenient testing. A series ammeter capable of measuring 10A or more should be used for both the input and the output lines. Dedicated voltmeters should be connected with their positive and negative leads right at the four power terminals at the sides of the evaluation board. This measurement technique minimizes the resistive loss in the wires that connect the evaluation board to the input power supply and the electronic load. Output voltage ripple measurements should be taken directly across the 100 nF ceramic capacitor Cox, placed right between the output terminals. Care must be taken to minimize the loop area between the oscilloscope probe tip and the ground lead. One method to minimize this loop is to remove the probe's spring tip and `pigtail' ground lead an
d then wind bare wire around the probe shaft. The bare wire should contact the ground of the probe, and the end of the wire can then contact the ground side of Cox. Figure 5 shows a diagram of this method.

Example Circuit
The example circuit which comes on the evaluation board delivers a 48V 2% output voltage at currents up to 700 mA and switches at 600 kHz. The input voltage range is optimized between 10.8V and 26.4V. The measured efficiency of the converter is 96% at an input voltage of 24V and an output current of 0.7A.

MOSFET Footprints
The LM3430 evaluation board has a footprint for a single MOSFET with an SO-8 package using the industry standard pinout. (See Figure 2) This footprint can also accept newer MOSFET packages that are compatible with SO-8 footprints.

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FIGURE 1. Efficiency

Powering The Converter
The example circuit for the LM3430 Evaluation Board is optimized to run at inputs of 12V or 24V, however the circuit will operate with input voltages ranging from 6.0V to 40.0V connected between the `VIN' and `GND' terminals on the right side of the board. Fixed loads, resistors, and variable electronic loads can be connected between the `Vo' and `GND' terminals on the left side of the board. The Bill of Materials table lists all the components used in the example circuit.
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FIGURE 2. SO-8 MOSFET Pinout

Enabling The Converter
The OFF terminal controls the state of the converter while power is applied to the input terminals. The LM340 is disabled whenever the voltage at OFF is a logic high. (Above 2.0V.) The LM3430 is enabled whenever the OFF terminal is opencircuited or connected to ground. Upon enabling the LM3430 will perform a soft-start, after which the output is ready to supply current to the load.

AN-1529

2007 National Semiconductor Corporation

202097

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