DEMO MANUAL DC1887A LTC3128 High Efficiency 2-Cell Supercapacitor Charger and Balancer Converter Description Demonstration circuit 1887 is a DC/DC supercapacitor buck-boost charger and balancer converter featuring the LTC®3128. The DC1887A operates over 1.72V to 5.5V input and charges the output up to 5.5V. Also, the LTC3128 has 2% precision input current limit, which allows the circuit to operate effectively with current limited input power sources like the USB. The 1.2MHz switching frequency operation results in a small and efficient circuit. The converter provides high output voltage accuracy (typically ±2%) over a 1.72V to 5.5V input. The demonstration circuit can be easily modified to generate different output voltages. Performance Summary The DC1887 has a small circuit footprint. It is a high performance and cost effective solution for charging and balancing supercapacitors. Please read the LTC3128 data sheet along with this manual. Design files for this circuit board are available at http://www.linear.com/demo L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Specifications are at TA = 25°C PARAMETER CONDITIONS VALUE Minimum Input Voltage IOUT = 0A to 1A 1.72V Maximum Input Voltage IOUT = 0A to 1A 5.5V VOUT VIN = 1.72V to 5.5V, IOUT = 0A 4.2V ±2% Input Current Limit (Programmable to 3A) VIN = 1.72V to 5.5V 0.9A Nominal Switching Frequency 1.2MHz dc1887af 1 DEMO MANUAL DC1887A Quick Start Procedure Demonstration circuit 1887 is easy to set up to evaluate the performance of the LTC3128. For proper measurement equipment setup refer to Figure 1 and follow the procedure below: NOTE: When measuring the input or output voltage ripple, care must be taken to minimize the length of oscilloscope probe ground lead. Measure the input or output voltage ripple by connecting the probe tip directly across the VIN or VOUT and GND terminals as shown in Figure 2. + VOUT – COUT GND Figure 2. Measuring Input or Output Ripple 1.With power off, connect the input power supply to VIN and GND. 2.Keep the load set to 0A or disconnected. 3.Turn the input power source on and slowly increase the input voltage. Be careful not to exceed 5.5V. NOTE: Make sure that the input voltage VIN does not exceed 5.5V. 4.Set the input voltage to 3.3V and check for the proper output voltage of 4.2V. 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 voltage is established, adjust the load and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 6.Note that the output voltage VOUT will vary with load. This is due to the current source nature of the LTC3128 power converter. As the output voltage increases the output current will decrease in order to maintain the input current below the preset limit. The LTC3128 circuit maximizes the output current while keeping the input current within the preset current limit. This keeps the supercapacitor charging time to a minimum. CHANGING THE OUTPUT VOLTAGE To change the output voltage from the programmed 4.2V, change the voltage divider resistors connected to the LTC3128 FB pin (see the schematic on page 5). Figure 1. Proper Measurement Equipment Setup dc1887af 2 DEMO MANUAL DC1887A Quick Start Procedure CONVERTER OUTPUT CURRENT START-UP AND CURRENT LIMIT FUNCTION The DC1887 output current capability depends on the input voltage and programmed input current limit. Typical performance of the DC1887A is shown in Figure 3. As can be seen from Figure 3, the output current decreases as the output voltage is approaching the programmed output voltage of 4.2V. The DC1887 features an input current limit circuit that controls the inrush current and output voltage ramp at start-up and during recharge cycles. The input current limit of DC1887 is set to 900mA and it should be suitable for operation from a USB port. The input current limit can be seen in Figure 5. While charging the supercap, the current is constant. Once the output voltage is close to the set point the current limit is reduced in order to prevent output voltage overshoot. 1.2 1.0 The input current limit can be programmed up to 3A by changing the resistor R8 in the Schematic Diagram. IOUT (A) 0.8 0.6 OUTPUT VOLTAGE BALANCING 0.4 2V INPUT 3.3V INPUT 5V INPUT 0.2 0 1 1.5 2 2.5 3 VOUT (V) 3.5 4 4.5 dc1887 F03 Figure 3. The Output Current Decreases as the Supercap Voltage Increases Due to Precise Input Current Limit. OUTPUT LOAD STEP RESPONSE The load step response of DC1887A is dependent on the supercap used. If higher load steps need to be handled more output capacitance can be added in order to keep the voltage transients at the desired level. The load step transients are shown in Figure 4. The LTC3128 can charge two output capacitors in series that are not identical. The internal capacitor voltage balancing circuit can compensate for the difference in capacitance by moving the charge from the capacitor at a higher voltage (smaller cap) to a capacitor with a lower voltage (bigger cap). To see this effect, monitor VMID (VC3) and VOUT with a scope as shown in Figure 5. The trace 1 in Figure 5 is showing the top cap voltage (VC3 = VOUT – VMID). Figure 5. The DC1887 Ramps the Output Slowly at Start-Up without Generating an Input Current Surge. Figure 4. The Supercap Supplies Most of the Pulsed Load Current. The LTC3128 Makes a Small Contribution to Load Current as Shown in Figure 3. dc1887af 3 DEMO MANUAL DC1887A Parts List ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER Required Circuit Components 1 2 C2, C3 CAP, X5R, 10µF, 25V, 10%, 0805 AVX, 08053D106KAT2A 2 2 C1, C4 CAP, X5R, 10µF, 25V, 10%, 1206 MURATA, GRM31CR61E106KA12L 3 1 C5 CAP, NPO, 120pF, 25V, 10%, 0603 AVX, 06033A121JAT2A 4 3 C6, C7, C10 CAP, X5R, 1µF, 25V, 10%, 0603 AVX, 06033D105KAT2A 5 1 C8 SUPERCAP, 5.5V, 330mF MURATA, DMF3Z5R5H334M3DTA0 6 2 C9, C12 SUPERCAP, 10.0F, 2.7V, 10mm × 30mm ILLINOIS CAP, 106DCN2R7Q 7 1 L1 IND, POWER INDUCTOR, 3.3µH COILCRAFT: XAL6030-332MEB 8 1 R1 RES, CHIP, 1.87M, 1%, 0603 VISHAY, CRCW06031M87FKEA 9 1 R2 RES, CHIP, 0, 0603 VISHAY, CRCW06030000Z0EA 10 1 R3 RES, CHIP, 301k, 1%, 0603 VISHAY, CRCW0603301KFKEA 11 2 R5, R6 RES, CHIP, 1M, 1%, 0603 VISHAY, CRCW06031M00FKEA 12 1 R7 RES, CHIP, 127k, 1%, 0603 VISHAY, CRCW0603127KFKEA 13 1 R8 RES, CHIP, 12.1k, 0.1%, 0603 VISHAY, TNPW060312K1BEEA 14 1 U1 LTC3128EUFD, QFN 4mm × 5mm LINEAR TECHNOLOGY, LTC3128EUFD Additional Demo Board Circuit Components 1 0 C11 (OPT) CAP, 0603 2 0 R4 OPT RES, CHIP OPTIONAL Hardware: For Demo Board Only 1 10 E1 TO E10 TESTPOINT, TURRET, 0.095" MILL-MAX, 2501-2-00-80-00-00-07-0 2 1 JP1 0.079 SINGLE ROW HEADER, 3 PIN SAMTEC, TMM-103-02-L-S 3 2 JP3, JP4 0.079 DOUBLE ROW HEADER, 2X3 PIN SAMTEC, TMM-103-02-L-D 4 3 JP1, JP3, JP4 SHUNT SAMTEC, 2SN-BK-G STAND OFF 5 4 STAND OFF KEYSTONE, 8833 6 1 FAB, PRINTED CIRCUIT BOARD DEMO CIRCUIT 1887A 7 1 STENCIL STENCIL DC1887A dc1887af 4 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. A B C RSENS GND 1.72V - 5.5V VIN 5 E9 E4 VIN E1 E8 C11 1uF OPT C10 10uF + 6 OFF ON 2 JP1 RUN 4 5 2 3 1 C5 120pF C4 10uF 10V C1 10uF 10V VOUT VIN PFI 4 R8 12.1k 0.1% C7 1uF R4 OPT C6 1uF R2 0 U1 LTC3128EUFD MAXV PFO PGOOD MID FB VOUTS VOUTP VOUTP CUSTOMER NOTICE PROG RSENS RSENP RUN VIN PFI 3.3uH 10 8 12 13 11 14 15 16 3 THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS. LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE. 5 3 2 4 7 9 1 SW1 L1 3 SW2 4 17 GND 18 SW2 PFI JP3 MODE 1 3 19 SW1 GND 20 GND 6 VOUT 21 VOUT VIN 4 6 5 2 3 1 JP4 PULL UP SOURCE C3 10uF C8 330mF 5.5V C9 10F E10 E7 E5 E3 E6 VPWR PFO PGOOD GND MID 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 www.linear.com Fax: (408)434-0507 LTC Confidential-For Customer Use Only R6 1Meg R5 1Meg C12 10F VOUT VPWR VIN + + DATE 10-16-13 VOUT 4.2V / 1A Goran P. E2 APPROVED DESCRIPTION 1 PRODUCTION REVISION HISTORY DATE: N/A SIZE 2 LTC3128EUFD DEMO CIRCUIT 1887A Tuesday, November 12, 2013 IC NO. 1 SHEET 1 OF 1 2 REV. TECHNOLOGY HZ TITLE: SCHEMATIC Goran P. BUCK-BOOST SUPERCAPACITOR CHARGER AND BALANCER SCALE = NONE APP ENG. PCB DES. APPROVALS 127k R7 R3 301K R1 1.87Meg VOUT 2 REV V+ C2 10uF 3 BAL __ ECO 2 2 1 D 5 A B C D DEMO MANUAL DC1887A Schematic Diagram dc1887af 5 DEMO MANUAL DC1887A 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 dc1887af 6 Linear Technology Corporation LT 0214 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2014