DEMO MANUAL DC1798A LTC3869IGN-2 Dual, 2-Phase Synchronous Step-Down DC/DC Controllers DESCRIPTION Demonstration circuit 1798A is a Dual Output, Dual Phase 5A Synchronous Buck Converter featuring the LTC3869IGN-2. The entire circuit, including the bulk output capacitors, fit within a 1.04" × 0.94" area on all layers. The package style for the LTC3869IGN-2 is a 28-lead narrow plastic SSOP. DC1798A-A has an on-board sense resistor for current feedback, while the DC1798A-B is configured with a DCR sense circuit that allows the converter to use the inductors DCR as the sense element instead of the on-board sense resistors to save cost and board space and improves efficiency. The main features of the board include rail tracking, an internal 5V linear regulator for bias, RUN pins for each output, a PGOOD signal and a mode selector that allows the converter to run in CCM, pulse-skipping or Burst Mode operation. Synchronization to an external clock is also possible through some minor component changes. Two versions of the board are available. The input voltage range is 4.5V to 26V. The LTC3869 datasheet gives a complete description of the part, operation and application information. The datasheet must be read in conjunction with this demo manual for DC1798A. PERFORMANCE SUMMARY PARAMETER Design files for this circuit board are available at http://www.linear.com/demo L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo 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 4.5V Maximum Input Voltage 26V Output Voltage VOUT1 VIN = 6.5V to 26V, IOUT1 = 0A to 5A 3.3V±2% Output Voltage VOUT2 VIN = 6.5V to 26V, IOUT2 = 0A to 5A 2.5V±2% VIN = 26V, IOUT1 = 5A (20MHz BW) <30mVP-P* VIN = 26V, IOUT2 = 5A (20MHz BW) <30mVP-P* Typical Output Ripple VOUT Nominal Switching Frequency 400kHz DC1798A-A DC1798A-B Efficiency VOUT1 = 3.3V, IOUT1 = 5A; VIN = 16V 90%** Typical 91.0%** Typical See Figures 3 and 4 for efficiency curves VOUT2 = 2.5V, IOUT2 = 5A; VIN = 16V 87.5%* Typical 88.8%* Typical *Measured at bulk output capacitor **Optional Mosfet (Si4816BDY) will result in up to 0.4% improvement in efficiency at full load dc1798af 1 DEMO MANUAL DC1798A QUICK START PROCEDURE Demonstration circuit 1798A is easy to set up to evaluate the performance of the LTC3869IGN-2. Refer to Figure 1 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 2 for proper scope probe technique. 1. Make sure jumpers are in the following positions: JUMPER POSITION JP1 ON JP2 ON JP3 CCM 2. With power off, connect the input power supply to VIN and GND. Connect active loads to outputs. 3. Turn on the power at the input. NOTE. Make sure that the input voltage does not exceed 28V. 4. Check for the proper output voltages. VOUT1 = 3.234V to 3.366V, VOUT2 = 2.450V to 2.550V, NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 6. Different operating modes can be evaluated by changing position of jumper JP3. A 4 V VOUT1 Load V A POWER SUPPLY A V VOUT2 Load Figure 1. Proper Measurement Equipment Setup dc1798af 2 DEMO MANUAL DC1798A QUICK START PROCEDURE Figure 2. Measuring Output Voltage Ripple Rail Tracking Demonstration circuit 1798A is set up for coincident rail tracking where VOUT2 tracks VOUT1 and the ramp rate for VOUT1 is determined by the value of the TRK/SS1 capacitor at C6. This board can be modified on the bench for external rail tracking or for independent turn-on of the rails. For the latter case, the ramp-rate for VOUT1 and VOUT2 will be determined by their respective TRK/SS capacitors. Refer to Table 1 for tracking options and to the data sheet for more details. Inductor DCR Sensing and Resistor Sensing The two different versions of the board offer either an on-board sense resistor or an inductor DCR sense circuit for current feedback. The DCR sense circuit uses the resistive voltage drop across the inductor to estimate the current. In contrast to the traditional sense resistor current feedback, the DCR sensing circuit offers lower cost and higher efficiency, but results in less accurate current limit due to the large variation in the inductor resistance. Furthermore, this indirect current sensing method cannot detect inductor saturation and requires the use of ‘soft’ saturating inductors (such as powder iron) resulting in increased core losses or ‘hard’ saturating inductors (such as ferrite) with sufficiency high current ratings resulting in increased inductor size. The demonstration circuit 1798A is intended to demonstrate the feasibility of a high performance, high efficiency synchronous buck converter using a ‘hard’ saturating ferrite inductor with DCR sensing. The typical efficiency versus load current for each of the outputs is given in Figure 3 and Figure 4 respectively. An efficiency improvement of up to 1% is possible for the DCR sensing version. If further improvement in efficiency is required, the switching devices can be replaced by the optional MOSFET Q3 and Q4. Table 1. Output Tracking Options TRACK 1 DIVIDER TRK/SS1 CAPACITOR TRACK 1 DIVIDER TRK/SS1 CAPACITOR CONFIGURATION R10 R12 C R1 R4 C Soft Start Without Tracking VOUT1 VOUT2 0Ω OPEN 10nF OPEN OPEN 10nF Coincident Tracking: VOUT1 tracking External Ramp VOUT2 tracking VOUT1 63.4kΩ 20.0kΩ OPEN 43.2kΩ 20.0kΩ OPEN Ratiometric Tracking: VOUT2 tracking VOUT1 OPEN OPEN OPEN 63.4kΩ 20.0kΩ OPEN dc1798af 3 DEMO MANUAL DC1798A QUICK START PROCEDURE 100 95 EFFICIENCY (%) 90 85 80 75 6.5VIN, 3.3VOUT, DCR SENSE, 400kHz 16VIN, 3.3VOUT, DCR SENSE, 400kHz 6.5VIN, 3.3VOUT, RSENSE, 400kHz 16VIN, 3.3VVOUT, RSENSE, 400kHz 70 65 0 1 1 2 2 3 3 4 4 5 5 LOAD CURRENT (A) Figure 3. Typical Efficiency vs Load Current for A-A(RSENSE) and A-B(DCR SENSE) Boards, 3.3VOUT, 400kHz dc1798af 4 DEMO MANUAL DC1798A 100 95 EFFICIENCY (%) 90 85 80 75 6.5VIN, 2.5VOUT, DCR SENSE, 400kHz 16VIN, 2.5VOUT, DCR SENSE, 400kHz 6.5VIN, 2.5VOUT, RSENSE, 400kHz 16VIN, 2.5VOUT, RSENSE, 400kHz 70 65 0 1 1 2 2 3 3 4 4 5 5 LOAD CURRENT (A) Figure 4. Typical Efficiency vs Load Current for A-A(RSENSE) and A-B(DCR SENSE) Boards, 3.3VOUT, 400kHz dc1798af 5 DEMO MANUAL DC1798A PARTS LIST ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Cap., X5R, 4.7μF, 50V, 20%, 1206 Cap., X5R, 4.7μF, 16V, 20%, 0805 Cap., OS-CON, 22μF, 35V, SMT Cap., X5R, 22μF, 6.3V, 20%, 1206 Cap., POSCAP 220μF 4V 20%, D2E Size Cap., NPO, 22pF, 50V, 10%, 0603 Cap., NPO, 1000pF, 25V, 10%, 0603 Cap., X7R, 0.1μF, 50V, 10%, 0603 Cap., X5R, 1μF, 16V, 10%, 0603 Cap., X7R, 0.01μF, 50V, 10%, 0603 Cap., NPO, 330pF, 25V, 10%, 0603 Cap., X7R, 2200pF, 50V, 10%, 0603 Cap., NPO, 220pF, 25V, 10%, 0603 Schottky Diode 30V, SOD323 Inductor, 2.4μH Mosfet N-Ch.,Dual Res., Chip, 0.006, 0.5W, 5%, 1206 Res., Chip, 63.4k, 1/16W, 1%, 0603 Res., Chip 0Ω 1/16W, 0603 Res., Chip, 10, 1/16W, 1%, 0603 Res., Chip, 20k, 1/16W, 1%, 0603 Res., Chip, 100k, 1/16W, 1%, 0603 Res., Chip, 90k, 1/16W, 1%, 0603 Res., Chip, 30.1k, 1/16W, 5%, 0603 Res., Chip, 10, 1/16W, 5%, 0603 Res., Chip, 100K,1/16W, 5%, 0603 Res., Chip, 13K, 1/16W, 5%, 0603 I.C.LTC3869IGN-2, SSOP, 28 PIN Taiyo Yuden, UMK316BJ475ML-T Taiyo Yuden, EMK212BJ475MG-T SANYO, 35SVPD22M AVX, 12066D226MAT2A SANYO, 4TPE220MF AVX, 06035A220KAT2A AVX, 06033A102KAT2A AVX, 06035C104KAT AVX, 0603YD105KAT TDK, C1608X7R1H103K AVX, 06033A331KAT AVX, 06035C222KAT AVX, 06033A221KAT Central Semi., CMDSH-3TR Sumida, CDEP85NP-2R4MC-50 Fairchild Semi., FDS6982AS IRC, LRC-LRF1206LF-01-R006-J VISHAY, CRCW060363K4FKEA VISHAY, CRCW06030000Z0EA (2rls) VISHAY, CRCW060310R0FKEA VISHAY, CRCW060320K0FKEA VISHAY, CRCW0603100KFKEA VISHAY, CRCW060390K0FKEA VISHAY, CRCW060330K0JNEA VISHAY, CRCW060310R0JNEA VISHAY, CRCW0603100KJNEA VISHAY, CRCW060313K0FKEA LINEAR TECH., LTC3869IGN-2 Required Circuit Components 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 2 1 1 2 2 2 2 4 2 2 1 2 1 2 2 2 2 1 6 4 2 1 1 1 1 1 1 1 CIN1, CIN2 C13 CIN4 COUT2, COUT4 COUT1, COUT3 C3, C18 C7, C15 C4, C14, C19, C21 C5, C17 C1, C6 C12 C11, C9 C8, D1, D3 L2, L1 Q1, Q2 RSNS1, RSNS2 R30 R10, R16, R18, R35, R36, R40 R11, R14, R26, R29 R19, R20 R7 R9 R15 R21 R33 R25 U1 Additional Circuit Components 1 0 CIN5, CIN6 (OPT) Cap., 1206 2 0 C10, C16, C20 (OPT) Cap., 0603 Cap., POSCAP, D2E size 3 0 COUT5, COUT6 (OPT) 4 0 R1, R4, R12, R24, R32, R34, R39, Res., Chip, 0603 (OPT) R41, R6, R13, R17, R22, R23, R27 5 0 J1, J2 (OPT) Res., Chip, 1206 6 0 Q3, Q4 (OPT) Mosfet N-Ch.,Dual with Shottky Diode 1 13 E1-E13 Turret, Testpoint Mill Max, 2501-2-00-80-00-00-07-0 2 2 JP1, JP2 0.079 SINGLE ROW HEADER, 3 PIN SAMTEC, TMM-103-02-L-S 3 1 JP3 0.079 SINGLE ROW HEADER, 4 PIN SAMTEC, TMM-104-02-L-S 4 3 JP1, JP2, JP3 SHUNT, SAMTEC, 2SN-BK-G 5 4 STAND-OFF STAND-OFF, NYLON 0.25" tall KEYSTONE, 8831(SNAP ON) Hardware dc1798af 6 DEMO MANUAL DC1798A SCHEMATIC DIAGRAM dc1798af 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. 7 DEMO MANUAL DC1798A 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 dc1798af 8 Linear Technology Corporation LT 0611 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2011