DEMO MANUAL DC368A LT1763 500mA Low Noise Micropower LDO Regulator Description Demonstration circuit DC368A is a low noise micropower voltage regulator using the LT ®1763 in the 8-lead SO package. These circuits are used primarily in voltage controlled oscillators, RF power supplies and, in larger systems, as local regulators. The ability to tolerate a wide variety of output capacitors makes them ideal in space- and costsensitive systems. Design files for this circuit board are available at http://www.linear.com/demo/DC368A 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 TA = 25°C, VIN = 2.3V, VSHDN = 5V, ILOAD = 1mA, VOUT = 1.22V (JP2 set on Pins 1-2), unless otherwise specified. PARAMETER CONDITIONS MIN Input Voltage Range TYP 2.3 MAX UNITS 20 V Output Voltage (Note 1) 1.208 1.220 1.232 V Output Voltage (Note 1) VIN = 1.5V, JP2 on Pins 5-6 1.478 1.497 1.519 V Output Voltage (Note 1) VIN = 1.8V, JP2 on Pins 7-8 1.775 1.802 1.834 V Output Voltage (Note 1) VIN = 2.5V, JP2 on Pins 9-10 2.462 2.506 2.563 V Output Voltage (Note 1) VIN = 3V, JP2 on Pins 11-12 2.961 3.019 3.093 V Output Voltage (Note 1) VIN = 3.3V, JP2 on Pins 13-14 3.235 3.300 3.384 V Output Voltage (Note 1) VIN = 5V, JP2 on Pins 15-16 4.897 5.006 5.148 V Line Regulation ∆VIN = 2.3V to 20V 1 5 mV Quiescent Current ∆ILOAD = 0mA 30 50 µA Load Regulation ∆ILOAD = 1mA to 500mA 0.2 1 % SHDN Pin Threshold On-to-Off 1.8 V Output Voltage Noise 0.45 0.65 Off-to-On, ILOAD = 1mA 0.8 ILOAD = 500mA, BW = 10Hz to 100kHz 20 V µVRMS Note 1: Output voltage variations include ±1% tolerance of feedback divider network. For tighter voltage range, use lower tolerance resistors or use fixed voltage output devices. TYPICAL PERFORMANCE CHARACTERISTICS Typical Dropout Voltage 500 LT1763 (5V Output) 10Hz to 100kHz Output Noise DROPOUT VOLTAGE (mV) 450 400 TJ = 125C 350 300 250 VOUT 100µV/DIV TJ = 25C 200 150 100 50 0 0 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT (mA) COUT = 10µF IL = 500mA 1ms/DIV 1763 G02 1763 G01 dc368afb 1 DEMO MANUAL DC368A package and schematic diagrams LT1763CS8 TOP VIEW OUT 1 8 IN ADJ 2 7 GND GND 3 6 GND BYP 4 5 SHDN 1.22V C2 0.01µF S8 PACKAGE 8-LEAD PLASTIC SO IN E1 8 JP1 SHDN C1 1µF 7 6 5 E2 LT1763 IN OUT GND ADJ GND GND SHDN BYP C3 10µF 10V USER SELECT 1.5V R1 56.2k ADJ1 2 1 1.8V 4 2.5V R2 118k 6 2 8 3V R3 261k 3.3V R4 365k R5 422k 10 12 14 16 9 11 13 15 5V E3 R6 768k E4 OUT GND JP2 3 1 4 3 5 7 R7 249k DC368 F01 Figure 1. LT1763 500mA Low Noise Micropower LDO Regulator dc368afb 2 DEMO MANUAL DC368A PARTS LIST ITEM QUANTITY REFERENCE PART DESCRIPTION MANUFACTURE/PART # 1 0 ADJ1 OPT, 0402 2 1 C1 CAP., X5R 1µF 25V 10%, 0603 AVX 06033D105KAT2A 3 1 C2 CAP., X7R 0.01µF 16V 5%, 0402 AVX 0402YC103JAT1A 4 1 C3 CAP CER X7R 10µF 10V, 1210 TAIYO YUDEN LMK325BJ106MN 5 4 E1 to E4 TP, TERMINAL TURRET, 1 PIN, 0.064 HOLE Mill-Max 2308-2 6 1 JP1 JMP, 2 PINS 1 ROW .079CC COMM-CON 2802S-02-G1 7 1 JP2 CONN, SMT2X8, 0.39” GAP COMM-CON 6351-16P1 8 1 SHUNTS FOR JP1 SHUNTS, .079” CENTER COMM-CON CCIJ2MM-138G 9 1 SHUNTS FOR JP2 SHUNTS 0.39CC COMM-CON CTAIJ1MM-G 10 1 R1 RES., CHIP 56.2k 1/16W 1% 0402 AAC CR05-5622FM 11 1 R2 RES., CHIP 118k 1/16W 1% 0402 AAC CR05-1183FM 12 1 R3 RES., CHIP 261k 1/16W 1% 0402 AAC CR05-2613FM 13 1 R4 RES., CHIP 365k 1/16W 1% 0402 AAC CR05-3653FM 14 1 R5 RES., CHIP 422k 1/16W 1% 0402 AAC CR05-4223FM 15 1 R6 RES., CHIP 768k 1/16W 1% 0402 AAC CR05-7683FM 16 1 R7 RES., CHIP 249k 1/16W 1% 0402 AAC CR05-2493FM 17 1 U1 IC, LT1763CS8, SO8 LINEAR TECH. LT1763CS8 dc368afb 3 DEMO MANUAL DC368A OPERATION Hook-Up Solid turret terminals are provided for easy connection to supplies and test equipment. Connect a 0V to 20V, 0.6A power supply across the IN and GND terminals and the load across the OUT and GND terminals. The SHDN pin can be disconnected from IN via JP1 to allow for separate shutdown control via a secondary control line. JP2 can be used to select any of a number of common fixed output voltages, or used in conjunction with ADJ1 to create a custom output voltage using the formula: pole. A 0.01µF capacitor lowers the output voltage noise to 20µVRMS. Using a bypass capacitor also improves transient response. With no bypassing and a 10µF output capacitor, a 10mA to 500mA load step settles to within 1% of final value in under 100µs. With a 0.01µF bypass capacitor, the output settles to within 1% for the same load step in under 10µs; total output deviation is inside 2.5%. Regulator start-up time is inversely proportional to bypass capacitor size, slowing to 15ms with a 0.01µF bypass capacitor and 10µF at the output. ADJ1 = (VOUT – 1.22V)/4.93µA Output Capacitance and Transient Response Thermal Characteristics The regulators are designed to be stable with a wide range of output capacitors. Output capacitor ESR affects stability, most notably with small capacitors. A 3.3µF minimum output value with ESR of 3Ω or less is recommended to prevent oscillation. Transient response is a function of output capacitance. Larger values of output capacitance decrease peak deviations, providing improved transient response for large load current changes. Bypass capacitors, used to decouple individual components powered by the regulator, increase the effective output capacitor value. Larger values of reference bypass capacitance dictate larger output capacitors. For 100pF of bypass capacitance, 4.7µF of output capacitor is recommended. With 1000pF or more of bypass capacitance, a 6.8µF output capacitor is required. Demonstration Circuit DC368A has been laid out to illustrate and achieve maximum power handling capabilities. Although a simple two-layer board might have been sufficient for electrical operation of the LT1763, the four-layer board with vias to internal ground planes offers excellent thermal characteristics. A two-layer board of the same size with no thermal vias will exhibit a thermal resistance of 60°C/W, whereas DC368A exhibits a thermal resistance of 50°C/W. Output Capacitor Selection The output capacitor C3 is a 10µF X7R ceramic chip capacitor. Should a different output capacitor be desired, care must be exercised with the selection. Many ceramic capacitor dielectrics exhibit strong temperature and voltage characteristics that reduce their effective capacitance to as low as 10% to 20% of nominal over the full temperature range. For further information, see Linear Technology Application Note 83, “Performance Verification of Low Noise, Low Dropout Regulators,” Appendix B, “Capacitor Selection Considerations,” reprinted below. capacitor selection considerations Bypass Capacitance and Low Noise Performance Adding a capacitor between the regulator’s VOUT and BYP pins lowers output noise. A good quality, low leakage capacitor is recommended. This capacitor bypasses the regulator’s reference, providing a low frequency noise The shaded region of Figure B1 defines the regulator’s stability range. The minimum ESR needed is set by the amount of bypass capacitance used, while maximum ESR is 3Ω. Ceramic Capacitors Ceramic capacitors require extra consideration. They are manufactured with a variety of dielectrics, each with different behavior across temperature and applied voltage. The most common dielectrics are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics provide high capacitance in a small package, but exhibit strong voltage and temperature coefficients, as shown in Figures B2 and B3. Used with a 5V regulator, a 10µF Y5V capacitor shows values as low as 1µF to 2µF over the operating temperature range. The X5R and X7R dielectrics have dc368afb 4 DEMO MANUAL DC368A OPERATION more stable characteristics and are more suitable for output capacitor use. The X7R type has better stability over temperature, while the X5R is less expensive and available in higher values. Voltage and temperature coefficients are not the only problem sources. Some ceramic capacitors have a piezoelectric response. A piezoelectric device generates voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor, the stress can be induced by vibrations in the system or thermal transients. The resulting voltages can cause appreciable amounts of noise, especially when a ceramic capacitor is used for noise bypassing. A ceramic capacitor produced Figure B4’s trace in response to light tapping from a pencil. Similar vibration-induced behavior can masquerade as increased output voltage noise. 4.0 20 3.5 STABLE REGION 2.5 ESR (Ω) CHANGE IN VALUE (%) 0 3.0 2.0 CBYP = 0 CBYP = 100pF 1.5 1.0 0.5 0 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF CBYP = 330pF CBYP≥1000pF –40 –60 Y5V –80 –100 3 2 4 5 6 7 8 9 10 OUTPUT CAPACITANCE (µF) 1 X5R –20 0 2 4 8 6 10 12 DC BIAS VOLTAGE (V) DC368 B1 Figure B1. LT1763 Regulator Stability for Various Output and Bypass (CBYP) Capacitor Characteristics 14 16 DC368 B2 Figure B2. Ceramic Capacitor DC Bias Characteristics Indicate Pronounced Voltage Dependence. Device Must Provide Desired Capacitance Value at Operating Voltage 40 CHANGE IN VALUE (%) 20 X5R 0 –20 –40 Y5V –60 –80 20µV/DIV BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF –100 –50 –25 0 50 25 75 TEMPERATURE (C) 100 125 DC368 B2 Figure B3. Ceramic Capacitor Temperture Characteristics Show Large Capacitance Shift. Effect Should Be Considered When Determining Circuit Error Budget 20µV/DIV DC368 B4 Figure B4. A Ceramic Capacitor Responds to Light Pencil Tapping. Piezoelectric Based Response Approaches 80µVP-P dc368afb 5 DEMO MANUAL DC368A operation Output Voltage Noise Measuring output voltage noise can be a tricky process, further complicated by the low levels of noise inherent in a circuit such as this. Consideration must be given to regulator operating conditions, as well as the noise bandwidth of interest. Linear Technology has invested an enormous amount of time to provide accurate, relevant data to customers regarding noise performance. For further information on measuring output voltage noise, see Linear Technology Application Note 83, “Performance Verification of Low Noise, Low Dropout Regulators.” Noise Testing Considerations What noise bandwidth is of interest and why is it interesting? In most systems, the range of 10Hz to 100kHz is the information signal processing area of concern. Additionally, linear regulators produce little noise energy outside this region.1 These considerations suggest a measurement bandpass of 10Hz to 100kHz, with steep slopes at the band limits. Figure 2 shows a conceptual filter for LDO noise testing. The Butterworth sections are the key to IN 5Hz SINGLE ORDER HIGHPASS GAIN = 60dB 10Hz 2nd ORDER BUTTERWORTH HP steep slopes and flatness in the passband. The small input level requires 60dB of low noise gain to provide adequate signal for the Butterworth filters. Figure 3 details the filter scheme. The regulator under test is at the diagram’s center.2 A1–A3 make up a 60dB gain highpass section. A1 and A2, extremely low noise devices (<1nV√Hz), comprise a 60dB gain stage with a 5Hz highpass input. A3 provides a 10Hz, 2nd order Butterworth highpass characteristic. The LTC®1562 filter block is arranged as a 4th order Butterworth lowpass. Its output is delivered via the 330µF‑100Ω highpass network. The circuit’s output drives a thermally responding RMS voltmeter.3 Note that all circuit power is furnished by batteries, precluding ground loops from corrupting the measurement. Note 1: Switching regulators are an entirely different proposition, requiring very broadband noise measurement. Note 2: Component choice for the regulator, more critical than might be supposed, is discussed in “Capacitor Selection Considerations.” Note 3: The choice of the RMS voltmeter is absolutely crucial to obtaining meaningful measurements. See Appendix C, Application Note 83 “Understanding and Selecting RMS Voltmeters.” 100kHz 4th ORDER BUTTERWORTH LP 5Hz SINGLE ORDER HIGHPASS 10Hz TO 100kHz DC368 F02 Figure 2. Filter Structure for Noise Testing LDOs. Butterworth Sections Provide Appropriate Response in Desired Frequency Range dc368afb 6 DEMO MANUAL DC368A operation EXTERNAL INPUT + + 330µF + INPUT 100Ω 100Ω A1 LT1028 6.19k 3.16k 1µF 4.99k A3 LT1224 – 2k 2.49k 5.9K VIN IN + NORMAL INPUT – – 4.5V 4.7µF 4.7µF A2 LT1028 –4.5V 5VOUT OUT LT1763-5 0.01µF SHDN BYP GND + 10µF RLOAD (TYPICALLY 150mA) TYPICAL REGULATOR UNDER TEST 10k 10k 1 20 5.62k 2 19 13k 10k 3 18 10k 4 17 5 16 6 15 7 14 110k 8 13 110k 17.8k 9 12 43.2k 10 11 –4.5V 4.5V 110k LTC1562 –4.5V OUTPUT TO THERMALLY RESPONDING RMS VOLTMETER 0.1V FULL SCALE = 100µVRMS NOISE 10Hz TO 100kHz BW 330µF 100Ω + ALL RESISTORS 1% METAL FILM 4.7µF CAPACITORS = MYLAR, WIMA MKS-2 330µF CAPACITORS = SANYO OSCON ±4.5V DERIVED FROM 6AA CELLS POWER REGULATOR FROM APPROPRIATE NUMBER OF D SIZE BATTERIES 110k DC368 F03 Figure 3. Implementation of Figure 2. Low Noise Amplifiers Provide Gain and Initial Highpass Shaping. LTC1562 Filter Supplies 4th Order Butterworth Lowpass Characteristic dc368afb 7 DEMO MANUAL DC368A pcb layout and film Silkscreen Top Paste Mask Top Solder Mask Top Layer 1, Component Side* Layer 4, Solder Side* Layer 3, GND Plane* Layer 2, GND Plane* Solder Mask Bottom * These layers are shorted to L1 with Vias and function as heat dispersants. dc368afb 8 DEMO MANUAL DC368A pc fab drawing 2.000 D A C 2.000 C A C D B C NOTES: UNLESS OTHERWISE SPECIFIED 1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ. COPPER CLAD THICKNESS 0.062 0.006 TOTAL OF 4 LAYERS. 2. FINISH: ALL PLATED HOLES 0.001 MIN./0.005 MAX. COPPER PLATE ELECTRODEPOSITED TIN-LEAD COMPOSITION BEFORE REFLOW. SOLDER MASK OVER BARE COPPER (SMOBC). 3. SOLDER MASK: BOTH SIDES USING LPI OR EQUIVALENT. 4. SILKSCREEN: USING WHITE EPOXY NON-CONDUCTIVE INK. 5. UNUSED SMD COMPONENTS SHOULD BE FREE OF SOLDER. 6. FILL UP ALL VIAS WITH SOLDER. 7. SCORING: 0.020 NUMBER SYMBOL DIAMETER OF HOLES A 0.02 25 B 0.035 2 C 0.064 4 D 0.07 2 TOTAL HOLES 33 PLATED YES YES YES NO 0.017 dc368afb 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. 9 DEMO MANUAL DC368A 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 dc368afb 10 Linear Technology Corporation LT 0713 REV B • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com LINEAR TECHNOLOGY CORPORATION 2001