User's Guide SNVU228 – April 2013 LM25017 Evaluation Board 1 Introduction The LM25017 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 10 V output over an input range of 12.5 V to 48 V. The board’s specifications are: • Input Range: 12.5 V to 48 V • Output Voltage: 10 V • Output Current: 650 mA • Nominal Switching Frequency ~ 480 kHz • Measured Efficiency: 90.
Theory of Operation 2 www.ti.com Theory of Operation When the circuit is in regulation, the buck switch is turned on each cycle for a time determined by R3 and VIN according to Equation 1: TON = 10 -10 x R2 VIN (1) The on-time of this evaluation board ranges from 1.95 µs at VIN = 12 V to 435 ns at VIN = 48 V. The ontime varies inversely with input voltage. At the end of each on-time, the buck switch is off for at least 144 ns. In normal operation, the off-time is much longer.
Bill of Materials (BOM) www.ti.com Designator Value Description Package Reference Part Number Manufacturer R3 6.98k RES, 6.98k ohm, 1%, 0.1W, 0603 0603 CRCW06036K98FKEA Vishay-Dale R4 0 RES, 0 ohm, 5%, 0.125W, 0805 0805 CRCW08050000Z0EA Vishay-Dale R5 46.4k RES, 46.4k ohm, 1%, 0.1W, 0603 0603 CRCW060346K4FKEA Vishay-Dale R6 1.00k RES, 1.00k ohm, 1%, 0.1W, 0603 0603 CRCW06031K00FKEA Vishay-Dale R7 14.0k RES, 14.0k ohm, 1%, 0.
Ripple Configuration 6 www.ti.com Ripple Configuration The LM25017 is a COT buck and requires adequate ripple at feedback (FB) node. Three commonly used ripple generation methods are shown in Table 1. LM25017 evaluation board has been supplied with minimum ripple configuration (Type 3), but can be configured to Type 1 or Type 2 with modifications as suggested in Table 1. Table 1.
Performance Curves www.ti.com 7 Performance Curves 100 Efficiency (%) 90 80 70 VIN=15V 60 VIN=24V VIN=36V 50 0 0.1 0.2 0.3 0.4 0.5 0.6 IOUT (A) 0.7 C001 Figure 2. Efficiency vs Load Current 550 500 FREQUENCY (kHz) 450 400 350 300 250 200 150 100 50 10 15 20 25 30 35 40 45 INPUT VOLTAGE (V) 50 C002 Figure 3. Frequency vs Input Voltage Figure 4.
PC Board Layout 8 www.ti.com PC Board Layout Figure 5. Top Silk Figure 6. Top Copper Figure 7.
EVALUATION BOARD/KIT/MODULE (EVM) ADDITIONAL TERMS Texas Instruments (TI) provides the enclosed Evaluation Board/Kit/Module (EVM) under the following conditions: The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user indemnifies TI from all claims arising from the handling or use of the goods.
FCC Interference Statement for Class B EVM devices This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications.
【Important Notice for Users of this Product in Japan】 】 This development kit is NOT certified as Confirming to Technical Regulations of Radio Law of Japan If you use this product in Japan, you are required by Radio Law of Japan to follow the instructions below with respect to this product: 1. 2. 3. Use this product in a shielded room or any other test facility as defined in the notification #173 issued by Ministry of Internal Affairs and Communications on March 28, 2006, based on Sub-section 1.
EVALUATION BOARD/KIT/MODULE (EVM) WARNINGS, RESTRICTIONS AND DISCLAIMERS For Feasibility Evaluation Only, in Laboratory/Development Environments. Unless otherwise indicated, this EVM is not a finished electrical equipment and not intended for consumer use.
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