DEMO MANUAL DC1736A LT3975 42V, 2.5A, 2.7µA Micropower Buck Regulator DESCRIPTION Demonstration circuit 1736A is a monolithic step-down DC/DC switching regulator featuring the LT®3975. The demo circuit is designed for 3.3V, 2.5A output from a 4.3V to 42V input. The wide input range of the LT3975 allows a variety of input sources, such as automotive batteries and industrial supplies. The switching frequency can be programmed either via oscillator resistor or external clock up to 2MHz. When the circuit is synchronized to an external clock connected to the SYNC terminal, the RT resistor (R5) should be chosen to set the LT3975 internal switching frequency at least 20% below the lowest synchronization input frequency. Low ripple Burst Mode® operation increases the efficiency at the light load while keeping the output ripple below 15mV. The circuit consumes only 2.7μA of quiescent current. The LT3975 internal boost diode and loop compensation reduce the components count and solution size. The current mode control scheme creates fast transient response and good loop stability. The LT3975 is in shutdown when PERFORMANCE SUMMARY PARAMETER the EN pin is low and active when the pin is high. The threshold of the EN pin is accurate at 1.02V with 60mV of hysteresis. Users can populate R7 and R8 to provide a programmable undervoltage lockout. During a short-circuit fault, the LT3975 has current limit foldback to limit the power dissipation. The LT3975 data sheet gives a complete description of the part, operation and application information. The data sheet must be read in conjunction with this demo manual for demo circuit 1736A. The LT3975 is assembled in a 16-lead plastic MSOP package with an exposed pad for low thermal resistance. Proper board layout is essential for both proper operation and maximum thermal performance. See the data sheet section PCB Layout and High Temperature Considerations. Design files for this circuit board are available at http://www.linear.com/demo L, LT, LTC, LTM, μModule, Linear Technology, the Linear logo and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. TA = 25°C CONDITIONS VALUE Minimum Input Voltage 4.3V Maximum Input Voltage 42V Output Voltage, VOUT VIN = 4.3V ~ 42V 3.3V ± 3% Switching Frequency RT = 78.7k 600kHz ±20% Maximum Output Current, IOUT VIN = 4.3V ~ 42V 2.5A Typical Efficiency VIN = 12V, IOUT = 2.5A 82.1% Typical Output Voltage Ripple VIN = 12V, IOUT = 2.5A, 25MHz BW 20mV dc1736af 1 DEMO MANUAL DC1736A QUICK START PROCEDURE Demonstration circuit 1736A is easy to set up to evaluate the performance of the LT3975. Refer to Figure 2 for proper measurement equipment setup and follow the procedure below: 5. Turn on the power at the input. NOTE. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VIN or VOUT and GND terminals. See Figure 3 for the proper scope technique. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 1. Place JP1 on the ON position. 8. An external clock can be added to the SYNC terminal when SYNC function is used (JP2 on the SYNC position). Please make sure that the SYNC frequency is at least 20% higher than the set switching frequency. See the data sheet section Synchronization. 2. Place JP2 on the RT FREQ position. 3. With power off, connect the input power supply to VIN and GND. NOTE. Make sure that the input voltages do not exceed 42V. 6. Check for the proper output voltage (3.3V). 7. Once the proper output voltages are established, adjust the load within the operating ranges and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 4. With power off, connect load from VOUT to GND. 90 85 EFFICIENCY (%) 80 75 70 65 60 VOUT = 3.3V VIN = 12V fSW = 600kHz 55 50 0 0.5 1 1.5 LOAD CURRENT (A) 2 2.5 DC1735A F01 Figure 1. Efficiency vs Load Current dc1736af 2 DEMO MANUAL DC1736A QUICK START PROCEDURE – – V + – + VOUT + A LOAD – + – V VIN + – A + Figure 2. Proper Measurement Equipment Setup Figure 3. Measuring Output Ripple dc1736af 3 DEMO MANUAL DC1736A PARTS LIST ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 1 C1 Cap., X5R, 47μF 10V 20% 1210 TDK, C3225X5R1A476M 2 1 C2 Cap., X5R, 0.47μF 25V 10% 0603 TDK, C1608X5R1E474K 3 1 C3 Cap., X5R, 10μF 50V 10%, 1210 TDK, C3225X5R1H106K 4 1 C5 Cap., C0G, 10pF 50V 10%, 0402 TDK, C1005C0G1H100D 5 1 C6 Cap., X7R, 10nF 25V 10%, 0402 TDK, C1005X7R1E103K 6 1 D1 Diode, Scholtky, PowerDi5 DIODE INC, PDS360-13 7 1 L1 IND, 3.3μH VISHAY, IHLP2020CZER3R3M01 8 1 R1 Res., Chip, 1.00M 1/16W 1% 0402 VISHAY, CRCW04021M00FKED 9 1 R2 Res., Chip, 576k 1/16W 1% 0402 VISHAY, CRCW0402576KFKED 10 1 R5 Res., Chip, 78.7k 1/16W 1% 0402 VISHAY, CRCW040278K7FKED 11 1 R6 Res., Chip, 200k 1/16W 1% 0402 VISHAY, CRCW0402200KFKED 12 1 U1 I.C., MSE16 LINEAR TECH., LT3975EMSE Additional Circuits 13 1 C4 Cap., Elect.,100μF 50V 10% SUN ELECT, 50CE100BS 14 1 C7 Cap., X5R, 1μF 16V 20% 0603 AVX, 0603YD105MAT 15 0 R7, R8 Res., 0402 OPT Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0 Hardware—For Demo Board Only 16 7 E1, E2, E3, E4, E5, E6, E7 17 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S 18 2 Shunt Shunt, 2mm Ctrs. SAMTEC, 2SN-BK-G dc1736af 4 DEMO MANUAL DC1736A SCHEMATIC DIAGRAM dc1736af Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 5 DEMO MANUAL DC1736A DEMONSTRATION BOARD IMPORTANT NOTICE Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions: This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations. If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES. The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or agency certified (FCC, UL, CE, etc.). No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind. LTC currently services a variety of customers for products around the world, and therefore this transaction is not exclusive. Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and observe good laboratory practice standards. Common sense is encouraged. This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application engineer. Mailing Address: Linear Technology 1630 McCarthy Blvd. Milpitas, CA 95035 Copyright © 2004, Linear Technology Corporation dc1736af 6 Linear Technology Corporation LT 0712 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2012