DEMO MANUAL DC2246B LT3042EDD 20V, 200mA, Ultralow Noise Ultrahigh PSRR RF LDO Regulator DESCRIPTION DC2246B is a linear regulator featuring the LT®3042EDD, which is a 200mA, ultralow noise, and ultrahigh power supply rejection ratio (PSRR) RF low dropout (LDO) regulator with programmable current limit. DC2246B operates over an input voltage range of 3.8V to 20V. The LT3042 has a maximum output current of 200mA. It features ultralow noise (0.8µVRMS from 10Hz to 100kHz) and very high PSRR (79dB at 1MHz). The power good feedback (PGFB) pin voltage is programmable for power good threshold. A current limit function is provided. Current monitoring is also achievable by sensing the voltage on the ILIM pin. Built-in protection includes reverse battery protection, reverse current protection, internal current limit with foldback and thermal limit with hysteresis. The LT3042 data sheet gives a complete description of the device, operation and applications information. The data sheet must be read in conjunction with this Demo Manual for demonstration circuit DC2246B. The LT3042EDD is assembled in a 10-lead (3mm × 3mm) plastic DFN package with an exposed pad on the bottom-side of the IC. Proper board layout is essential for maximum thermal performance. Design files for this circuit board are available at http://www.linear.com/demo/DC2246B 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. PERFORMANCE SUMMARY Specifications are at TA = 25°C PARAMETER CONDITIONS MIN Input Voltage Range (VIN) VOUT = 3.3V 3.8 TYP MAX UNITS 20 VDC 3.4 VDC Shutdown Input Current (IIN) JP1 = OFF, VIN = 6V Output Voltage (VOUT) VIN = 5V, IOUT = 200mA 0.1 Output Current Range (IOUT) VIN = 3.8V~19.7V, VOUT = 3.3V 0 200 mA Output Current Range (IOUT) VIN = 3.8V~20V, VOUT = 3.3V 0 195* mA 3.2 3.3 µA * Please refer to the Current Limit vs Input-to-Output Differential in the LT3042 data sheet. dc2246bfa 1 DEMO MANUAL DC2246B BOARD PHOTO dc2246bfa 2 DEMO MANUAL DC2246B QUICK START PROCEDURE The DC2246B is easy to set up to evaluate the performance of the LT3042EDD. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1. Connect Load between the VOUT and GND terminals. 2. With power off, connect the input power supply to the VIN and GND terminals. voltage is between 3.8V and 20V. 5. Refer to Application Notes AN70 and AN159 for measuring the output noise and PSRR. 6. R2 and R4 can define an accurate undervoltage lockout (UVLO) threshold when the shunt of JP1 is at USER SELECT option. 3. Make sure the shunt of JP1 is at ON option. 4. Turn the input power supply on and make sure the *J1 AND J2 ARE THE BNC CONNECTORS TO COAXIAL CABLE FOR NOISE MEASUREMENT, PLEASE REFER TO AN70 APPENDIX B FOR DETAILS. *THE MAXIMUM OUTPUT CURRENT WILL DECREASE FROM 200mA TO 195mA AT VIN = 20V. Figure 1. Test Procedure Setup Drawing for DC2246B dc2246bfa 3 DEMO MANUAL DC2246B PCB LAYOUT Best PSRR Performance: PCB Layout for Input Trace For applications utilizing the LT3042 for post-regulating switching converters, placing a capacitor directly at the LT3042 input results in AC current (at the switching frequency) to flow near the LT3042. Without careful attention to PCB layout, this relatively high frequency switching current generates an Electromagnetic Field (EMF) that couples to the LT3042 output, thereby degrading its effective PSRR. While highly dependent on the PCB, the switching preregulator, the input capacitor size, among other factors, the PSRR degradation can easily be 30dB at 1MHz. This degradation is present even if the LT3042 is de-soldered from the board, because it effectively degrades the PSRR of the PC board itself. While negligible for conventional low PSRR LDOs, LT3042’s ultrahigh PSRR requires careful Figure 2. Layer 3 of the DC2246B attention to higher order parasitics in order to realize the full performance offered by the regulator. The LT3042 demo board alleviates this degradation in PSRR by using a specialized layout technique. On layer 3, the input trace (VIN) is highlighted in red, with the return path (GND) highlighted on the bottom layer together with input capacitor C1. When an AC voltage is applied to the input of the board, AC current flows on this path, thus generating EMF. This EMF couples to output capacitor C2 and related traces, making the PSRR appear worse than it actually is. With the input trace directly above the return path, the EMFs are in opposite directions, and consequently cancels each other out. Making sure these traces exactly overlap each other maximizes the cancellation effect and thus provides the maximum PSRR offered by the regulator. Figure 3. Bottom Layer of the DC2246B dc2246bfa 4 DEMO MANUAL DC2246B PCB LAYOUT Best AC Performance: PCB Layout for Output Capacitor C2 For ultrahigh PSRR performance, the LT3042 bandwidth is made quite high (~1MHz), making it close to the output capacitor’s self-resonance frequency (~2MHz). Therefore, it is very important to avoid adding extra impedance (ESL and ESR) outside the feedback loop. To that end, minimize the effects of PCB trace and solder inductance by Kelvin connecting OUTS and SET pin capacitor (C4) GND directly to output capacitor (C2) terminals using split capacitor techniques. Pad 4 connects to the OUTS pin and Pad 1 connects to the GND side of the SET pin capacitor. With only small AC current flowing through these connections, the impact of solder joint/PCB trace inductance on stability is eliminated. While the LT3042 is robust enough not to oscillate if the recommended layout is not followed, phase/ gain margin and stability will degrade. VIN IN LT3042 100µA CIN EN/UV PGFB VOUT OUT PG OUTS SET RSET GND ILIM 4 3 1 2 C2 CSET Figure 4. C2 and CSET Connections for Best Performance Figure 5. Split Pads for C2 on Top Layer of DC2246B dc2246bfa 5 DEMO MANUAL DC2246B PARTS LIST ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER CAP., ALUM, 22µF, 35V, 5X5.4MM SUN ELEC., 32CE22BSS Required Circuit Components 1 1 CIN 2 3 C1, C2, C4 CAP., X7R, 4.7µF, 25V, 10%, 1206 MURATA, GRM31CR71E475KA88L 3 1 R1 RES., CHIP, 200k, 1/16W, 5% 0603 VISHAY, CRCW0603200KJNEA 4 1 R3 RES., CHIP, 33.2k, 1/8W, 1% 0603 VISHAY, CRCW060333K2FKEA 5 1 R5 RES., CHIP, 453k, 1/8W, 1% 0603 VISHAY, CRCW0603453KFKEA 6 1 R6 RES., CHIP, 49.9k, 1/8W, 1% 0603 VISHAY, CRCW060349K9FKEA 7 1 R7 RES., CHIP, 510Ω, 1/10W, 1% 0603 VISHAY, CRCW0603510RFKEA 8 1 U1 IC, LT3042EDD DFN 3X3MM LINEAR TECH., LT3042EDD#PBF VISHAY, CRCW06030000Z0EA Optional Electronic Components 1 1 R8 RES., CHIP, 0Ω, 1/16W, 5% 0603 2 0 R2, R4 (OPT) RES., OPT, 0603 3 0 C3, C5(OPT) CAP., OPT, 1206 Hardware: For Demo Board Only 1 6 E1-E6 TESTPOINT, TURRET, 0.094" PBF MILL-MAX, 2501-2-00-80-00-00-07-0 2 1 JP1 HEADER 3 PIN 0.079" DOUBLE ROW WURTH ELEKTRONIK, 62000621121 3 1 XJP1 SHUNT, 0.079" CENTER WURTH ELEKTRONIK, 60800213421 4 2 J1, J2 CONN, BNC, 5 PINS CONNEX, 112404 5 4 MH1-MH4 STAND-OFF, NYLON 6.4MM WURTH ELEKTRONIK, 702931000 dc2246bfa 6 E2 PG EN/UV INPUT RIPPLE MONITOR GND E4 J1 CIN 22µF 35V E3 + C1 4.7uF 25V 1206 R4 OPT R2 OPT 5 3 1 JP1 EN/UV R8 0 ON 4 USER SELECT 6 OFF R1 200K 2 C5 OPT 1206 4 3 2 1 PG EN/UV IN IN R7 510 5 35CE22BSS ILIM 11 E1 GND 8 VIN 3.8V-20V OUT SET PGFB OUTS GND U1 LT3042EDD 7 6 9 10 R3 33.2K R6 49.9K C2 4.7uF 25V 1206 J2 GND OUTPUT NOISE MONITOR E6 VOUT 1. ALL RESISTORS ARE 0603. * 3.3V, 200mA NOTE: UNLESS OTHERWISE SPECIFIED C4 4.7uF 25V 1206 R5 453K C3 E5 OPT 1206 * SEE DEMO MANUAL DEMO MANUAL DC2246B SCHEMATIC DIAGRAM dc2246bfa 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 DC2246B 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 dc2246bfa 8 Linear Technology Corporation LT 1116 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2015