LM34910EVAL

User's Guide SNVA099A – November 2004 – Revised April 2013 AN-1349 LM34910 Evaluation Board 1 Introduction The LM34910EVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 5V output from an input range of 8V - 36V. The circuit provides load currents >1A, with the current limit set at ≊1.3A The board’s specification are: • Input Voltage: 8V to 36V • Output Voltage: 5V, ±3% • Maximum Continuous Output current: 1.0A • Current Limit: 1.3A • Measured Efficiency: 92% (VIN = 8V, IOUT = 400 mA) • Switching Frequency: ≊850 kHz • Size: 0.75 in. x 1.5 in. x 0.47 in 55101 2305-001 REV A R1 C5 J1 IN C6 C4 OUT1 GND U1 R3 R5 D1 L1 NATIONAL SEMICONDUCTOR LM34910 LLP C2002 GND C2 OUT2 R4 R2 C1 J3 C3 Figure 1. Evaluation Board - Top Side 2 Theory of Operation Refer to the board’s schematic in Figure 2, which contains a simplified block diagram of the LM34910. When the circuit is in regulation, the buck switch is on each cycle for a time determined by R1 and VIN. The on-time in this evaluation board will range from ≊775 ns at VIN = 8V, to ≊200 ns at VIN = 36V. At the end of the on-time, the feedback voltage at FB is above 2.5V, and the Minimum Off-Timer ensures the buck switch is off for at least 280 ns. In normal operation, the off-time is longer. During the off-time, the output capacitor (C6) discharges, and when the output voltage falls so that the voltage at FB is below 2.5V, the comparator output switches to initiate a new on-time. As required by the datasheet, this circuit provides a minimum of 25 mVp-p ripple at the FB pin. Refer to the LM34910 data sheet for a more detailed block diagram, and a complete description of the various functional blocks. All trademarks are the property of their respective owners. SNVA099A – November 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated AN-1349 LM34910 Evaluation Board 1 Board Layout and Probing 3 www.ti.com 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: 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. 4 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. 5 Low Ripple Output The ripple voltage at OUT1 will range from ≊60 mVp-p (at VIN = 8V) to ≊160 mVp-p (at VIN = 36V). If a low ripple output is desired, connect the load to OUT2. The ripple at this output varies from ≊8 mVp-p to ≊26 mVp-p over the input voltage range. However, the load regulation is not as good at OUT2 as it is at OUT1 due to the presence of R4. 6 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 8 - 36V Input VIN C1 2.2 PF C2 R1 38.3k VCC LM34910 10 9 0.1 PF Minimum Off Timer On Timer BST 2 C4 C3 0.1 PF 0.022 PF L1 10 PH RON/SD SW 8 C5 0.022 PF Logic SS 7 1 ISEN 2.5V 3 5V VOUT1 D1 R2 2.0k R5 R4 0.22 VOUT2 SGND FB R3 2.0k 4 6 5 RTN C6 22 PF GND Figure 2. Board Schematic Table 1. Bill of Materials 2 Item Description Mfg. Part No. Package Value C1 Capacitor TDK C3225X7R1H225K 1210 2.2 µF, 50V C2, 3 Capacitor TDK C1608X7R1H104K 0603 0.1 µF, 50V C4, 5 Capacitor TDK C1608X7R1H223K 0603 0.022 µF, 16V C6 Capacitor TDK C3216Y5V1A226Z 1206 22 µF, 10V AN-1349 LM34910 Evaluation Board SNVA099A – November 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated Increased Current Limit www.ti.com Table 1. Bill of Materials (continued) Item Description Mfg. Part No. Package Value D1 Schottky diode Zetex ZLLS2000 SOT-23-6 40V, 2.2A L1 Inductor TKD SLF6028T-100M1R3 6 mm x 6 mm 10 µH, 1.3A R1 Resistor TDK CRCW06033832F100 0603 38.3 kΩ R2, 3 Resistor TDK CRCW06032001F100 0603 2.0 kΩ R4 Resistor Panasonic ERJ6RQFR22V 0805 0.22Ω, ⅛W R5 Resistor See data sheet 0805 U1 Switching Regulator LM34910 WSON-10 100 VIN = 8V EFFICIENCY (%) 90 _ VIN = 24V 80 VIN = 36V _ 70 _ 60 0 200 400 600 800 1000 LOAD CURRENT (mA) Figure 3. Efficiency vs Load Current EFFICIENCY (%) 100 90 _ 80 Load Current = 600 mA 70 0 _ 10 _ 20 30 40 VIN (V) Figure 4. Efficiency vs VIN SNVA099A – November 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated AN-1349 LM34910 Evaluation Board 3 PCB Layout 7 www.ti.com PCB Layout Figure 5. Board Silkscreen Figure 6. Board Top Layer Figure 7. Board Bottom Layer 4 AN-1349 LM34910 Evaluation Board SNVA099A – November 2004 – Revised April 2013 Submit Documentation Feedback Copyright © 2004–2013, Texas Instruments Incorporated IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. Buyers should obtain the latest relevant information before placing orders and should verify that such information is current and complete. All semiconductor products (also referred to herein as “components”) are sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment. TI warrants performance of its components to the specifications applicable at the time of sale, in accordance with the warranty in TI’s terms and conditions of sale of semiconductor products. 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