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LM34910 Evaluation Board

National Semiconductor Application Note 1349 Dennis Morgan November 2004

LM34910 Evaluation Board
National Semiconductor Application Note 1349 Dennis Morgan November 2004
Introduction
FIGURE 1. Evaluation Board - Top Side
Theory of Operation
1) When operating at high input voltage and high load current, forced air flow IS NECESSARY. 2) The LM34910, and the diode D1 will be hot to the touch when operating at high input voltage and high load current. 3) Use CAUTION when probing the circuit due to the compact layout. 4) At maximum load current (1A), the wire size and length used to connect the load becomes important. Ensure there is not a significant drop in the wires.
Board Connection / Start-up
The input connections are made to the J1 connector. The load is normally connected to the OUT1 and GND terminals of the J3 connector. Ensure the wires are adequately sized for the intended load current. Before start-up a voltmeter should be connected to the input terminals, and to the output terminals. The load current should be monitored with an ammeter or a current probe. It is recommended that the input voltage be increased gradually to 8V, at which time the output voltage will be 5V. If that indicates correctly, then proceed with evaluating the circuit.
Board Layout and Probing
The pictorial in Figure 1 shows the placement of the circuit components. The following should be kept in mind when the board is powered:
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Low Ripple Output
Increased Current Limit
The evaluation board current limit activates at a load current of )1.3A. If it is desired to increase the current limit for a particular application, R5 must be added to the board. Refer to the data sheet to determine the appropriate value for this resistor
FIGURE 2. Board Schematic
Bill of Materials
Item C1 C2, 3 C4, 5 C6 D1 L1 R1 R2, 3 R4 R5 U1 Description Capacitor Capacitor Capacitor Capacitor Schottky diode Inductor Resistor Resistor Resistor Resistor Switching Regulator Mfg. Part No. TDK C3225X7R1H225K TDK C1608X7R1H104K TDK C1608X7R1H223K TDK C3216Y5V1A226Z Zetex ZLLS2000 TKD SLF6028T-100M1R3 TDK CRCW06033832F100 TDK CRCW06032001F100 Panasonic ERJ6RQFR22V See data sheet National Semi LM34910SD Package 1210 0603 0603 1206 SOT-23-6 6 mm x 6 mm 0603 0603 0805 0805 LLP-10 Value 2.2 µF, 50V 0.1 µF, 50V 0.022 µF, 16V 22 µF, 10V 40V, 2.2A 10 µH, 1.3A 38.3 k 2.0 k 0.22, 1 / 8W
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FIGURE 3. Efficiency vs Load Current
FIGURE 4. Efficiency vs VIN
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PCB Layout
Board Silkscreen
Board Top Layer
Board Bottom Layer
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LM34910 Evaluation Board
Notes
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