DEMO MANUAL DC1848A LT3976 40V, 5A, 2MHz Step-Down Switching Regulator with 3.3A Quiescent Current Description Demonstration circuit 1848A is a monolithic step-down DC/ DC switching regulator featuring the LT3976. The LT3976 is a compact, high efficiency, high speed monolithic stepdown switching regulator that consumes only 3.3A of quiescent current. The demo circuit is designed for 3.3V, 5A output from a 4.3V to 40V input. The switching frequency can be programmed either via oscillator resistor or external clock up to 2MHz. To synchronize to an external clock, move JP2 to SYNC and apply the external clock to the SYNC turret. The RT resistor (R5) should be chosen to set the LT3976 internal switching frequency at least 20% below the lowest synchronization input frequency. Low ripple Burst Mode(R) operation increases the efficiency at the light load while keeping the output ripple below 15mV. The SYNC pin on the demo board is grounded by default for low ripple burst mode operation. The LT3976 is in shutdown when 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 under voltage lockout. A low dropout voltage of 500mV is maintained when the input voltage drops below the programmed Performance Summary PARAMETER output voltage. During a short circuit fault, the LT3976 has current limit foldback to limit the power dissipation. The demo board has an EMI filter installed. The EMI performance of the demo board is shown on Figure 2. The limit in Figure 2 is EN55022 Class B. The figure shows the circuit passes the test with a wide margin. To use the EMI filter, the input should be tied to VEMI, not VIN. VEMI pad is on the back of the demo board. The LT3976 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 1848A. The LT3976 is assembled in a 16-lead plastic MSOP and 24-lead 5mm x 3mm QFN packages 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 sections for details. Design files for this circuit board are available at http://www.linear.com/demo L, LT, LTC, LTM, 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. Specifications are at TA = 25C CONDITIONS VALUE Minimum Input Voltage 4.3V Maximum Input Voltage 40V VIN = 4.3V ~ 40V 3.3V 3% Switching Frequency RT = 130k 400kHz 20% Guaranteed Maximum Output Current IOUT VIN = 4.3V ~ 40V 5A Typical Efficiency VIN = 12V, IOUT = 5A 82.1% Typical Output Voltage Ripple VIN = 12V, IOUT = 5A 20mV Output Voltage VOUT dc1848af 1 DEMO MANUAL DC1848A Performance Summary 87 VIN = 12V VOUT = 3.3V fS = 400kHz 86 EFFICIENCY (%) 85 84 83 82 81 80 0 0.5 1 1.5 2 2.5 3 3.5 LOAD CURRENT (A) 4 4.5 5 DC1848A F01 Figure 1. LT3976 Efficiency vs Load Current Figure 2. LT3976 Demo Board EMI Performance, Switching Frequency 400kHz Quick Start Procedure Demonstration circuit 1848A is easy to set up to evaluate the performance of the LT3976. Refer to Figure 3 for proper measurement equipment setup and follow the procedure below: 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 4 for the proper scope technique. 1.Place JP1 on the ON position. 2.Place JP2 on the RT FREQ position. 3.With power off, connect the input power supply to VIN and GND. Make sure that the input voltage does not exceed 40V. 4.With power off, connect load from VOUT to GND. 5.Turn on the power at the input. 6.Check for the proper output voltage (3.3V). NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 7.Once the proper output voltage is established, adjust the load within the operating ranges and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 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. dc1848af 2 DEMO MANUAL DC1848A Quick Start Procedure Figure 3. Proper Measurement Equipment Setup Figure 4. Measuring Input or Output Ripple dc1848af 3 DEMO MANUAL DC1848A Parts List ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Demo Board Circuit Components 1 2 C1, C8 Cap., X5R, 47F, 10V, 20% 1210 TDK, C325X5R1A476MT 2 1 C2 Cap., X5R, 0.47F, 25V, 10% 0603 TDK, C1608X5R1E474K 3 2 C3 Cap., X5R, 10F, 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 C7 Cap., C0G, 470pF, 50V, 10%, 0402 AVX, 04025A471KAT2A 7 1 D1 DIODE, Schottky, PowerDi5 DIODE INC., PDS540-13 8 1 L1 IND., 3.3H VISHAY, IHLP2525CZER3R3M01 9 1 R1 Res., Chip, 1.00M, 1/16W, 1% 0402 NIC, NRC04F1004TRF 10 1 R2 Res., Chip, 576K, 1/16W, 1% 0402 VISHAY, CRCW0402576KFKED 11 1 R3 Res., Chip, 2, 1/16W, 1% 0402 VISHAY, CRCW04022R00FKED 12 1 R5 Res., Chip, 130k, 1/16W, 1% 0402 VISHAY, CRCW0402130KFKED 13 1 R6 Res., Chip, 200k, 1/16W, 1% 0402 VISHAY,CRCW0402200KFKED 14 1 U1 I.C., MSE16 LINEAR TECH., LT3976EMSE Additional Demo Board Circuit Components 15 1 C11 Cap., X5R, 1F 16V 20%, 0603 AVX, 0603YD105MAT 16 1 C4 Cap., Elect.,100F, 50V, 10% SUN ELECT, 50CE100BS 17 1 C9 Cap., X5R, 10F, 50V, 10%,1210 TDK, C3225X5R1H106K 18 1 C10 Cap., Alum. Electro., 33F, 50V SUNCON, 50HVP33M 19 1 L2 Ind., 1.0H XAL4020 COILCRAFT, XAL4020-102MEC 20 1 L3 Ind., 3.3H XAL5030 COILCRAFT, XAL5030-332MEC 21 0 R7, R8 Res., 0402 OPT Hardware/Components (for Demo Board Only) 22 7 E1, E2, E3, E4, E5, E6, E7 Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0 23 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S 24 2 XJP1, XJP2 SAMTEC, 2SN-BK-G dc1848af 4 DEMO MANUAL DC1848A Schematic Diagram E3 E4 E6 E5 5 C3 10uF 50V 1210 R7 OPT 0603 4 10 11 VIN 12 VIN VIN BOOST SW SW SW 5 6 7 3 4 1 14 16 3 C2 0.47uF 0603 R5 130K 1% (400kHz) + C10 33uF 50V 50HVP33 R3 2 C7 470pF 2 VIN R2 576k 1% R1 1.00M 1% L1 3.3uH IHLP2525CZER3R3M01 D1 PDS540 L3 3.3uH XAL5030-332ME 2 C5 10pF VOUT JP2 C1 47uF 10V 1210 3 2 1 C8 47uF 10V 1210 SYNC 1 RT FREQ 1 E1 C11 1uF 16V 0603 E2 E7 VOUT 3.3V / 5A GND SYNC D C B A 5 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. 1 2 3 U1 LT3976EMSE PG 15 FB OUT 13 EN 2 C9 10uF 50V 1210 3 L2 1.0uH XAL4020-102ME RT SYNC SS C6 10nF R6 200K VEMI NC VIN + C4 100uF 50V SUNCON 50CE100BS JP1 1 2 3 GND 9 VIN 4.3V - 40V GND PG EN ON OFF R8 OPT 0603 NOTES: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTORS ARE 0402. ALL CAPACITORS ARE 0402. 4 8 D C B A 5 NC 17 dc1848af DEMO MANUAL DC1848A 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 (c) 2004, Linear Technology Corporation dc1848af 6 Linear Technology Corporation LT 1012 * PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com LINEAR TECHNOLOGY CORPORATION 2012