QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502 1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER LT1767 DESCRIPTION Demonstration circuit 502 is a 1.25MHz 1.5A monolithic step-down DC/DC switching converter using the LT1767 buck regulator. With its fast switching speed, 1.5A internal power switch, and wide input voltage range, the LT1767 is a very versatile and powerful IC for DC/DC converters that require compact space and a wide variety of input voltage ranges. The constant 1.25MHz switching frequency allows all of the components to be very small, surface mount devices. The current-mode control topology creates fast transient response and good loop stability with a minimum number of external compensation components and ceramic input and output capacitors. The low resistance internal power switch (0.22Ω) maintains high efficiencies >80% and up to 90%. The SHDN pin and 6uA shutdown current extends battery life. The wide VIN range of the LT1767 allows step-down configurations from 3Vin up to 25Vin. Synchronization of switching frequencies up to 2MHz is possible. Demonstration Circuit 502 is a stepdown converter using the LT1767EMS8E. The circuit is designed for 6.6-25V input to 5.0V output @1A or for 4.525V† input to 3.3V output @1A for cable modem, handheld, automotive, and desktop computer applications. The output voltage is jumper selectable (5V or 3.3V). This board was designed for wide input voltage range applications where simplicity, small circuit size, and low component count are important as well as up to 1A of load current. The use of ceramic capacitors not only demonstrates small size and low cost, but the advantage of current-mode control in step-down applications with a simple compensation network and a place-holder for a feedforward capacitor for more rugged stability and optimal transient response if required. Design files for this circuit board are available. Call the LTC factory. † Higher input voltages may pulse-skip due to minimum on-time restrictions. Compensation component changes may be necessary to optimize pulse-skipping during high-temperature, high-voltage conditions and maintain control of switch current. Table 1. Typical Performance Summary PARAMETER CONDITION VALUE Input Voltage Range Vout = 5V (Jumper Selection) 6.6V–25V Input Voltage Range Vout = 3.3V (Jumper Selection) 4.5V–18V Vout Vout = 5V (Jumper Selection) 5V ±3% Vout Vout = 3.3V (Jumper Selection) 3.3V ±3% Maximum Output Current 1A Typical Switching Frequency 1.25MHz Typical Efficiency Vin = 12V, Vout = 5V, Iout = 1A 84% 1 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502 1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER QUICK START PROCEDURE Demonstration circuit 502 is easy to set up to evaluate the performance of the LT1767. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 4. Connect an ammeter in series with output load to measure output current. 5. Connect a voltmeter across the Vin and Gnd terminals to measure input voltage. NOTE: Make sure that the input voltage does not exceed 25V. 6. Connect a voltmeter across the Vout 1. Connect the 7V–25V or 4.5V–18V in- and Gnd terminal to measure output voltage. put power supply to the Vin and Gnd terminals on the board. 7. After all connections are made, turn on input power and verify that the output voltage is either 5.0V or 3.3V (the output voltage jumper setting). 2. Connect an ammeter in series with the input supply to measure input current. 3. Connect either power resistors or an electronic load to the Vout and Gnd terminals on the board. – 8. The synchronization and shutdown functions are optional and their pins can be left floating (disconnected) if their functions are not being used. + + + – – LTC1767EMS8E 1.25MHz Wide Input Range Step Down DC/DC Converter Demo Circuit 502 Linear Technology (408) 432-1900 www.linear.com Vin GND – Vout SHDN GND SYNC + VOUT 3.3V 5V + + – – + – LOAD Figure 1. Proper Measurement Equipment Setup 2 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502 100 100 90 90 80 80 5VOUT EFFICIENCY (%) 3.3VOUT EFFICIENCY (%) 1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER 70 60 50 5VIN 40 8VIN 30 12VIN 18VIN 20 60 50 8VIN 40 12VIN 30 18VIN 24VIN 20 10 10 0 0.01 70 0 0.1 1 0.01 LOAD CURRENT (mA) Figure 2. Efficiency for VOUT = 3.3V MINIMUM INPUT VOLTAGE The minimum LT1767 operating input voltage is 3.0V. However, a DC/DC buck converter needs to have an input voltage greater than the output voltage by a certain margin in order to provide the desired regulated output voltage. Maximum duty cycle, switch on-resistance, and inductor and diode DC losses all play a part in determining the minimum input voltage for a selected output over the full current range of the application. For this demonstration board, with up to 1A output current, the minimum input voltages required to maintain regulated output voltages is listed below. Customizable output voltages 2.5V and 1.8V are very common and are thus additionally listed in the table (see Customizing the Board below). If the input voltage falls below the minimum input voltage listed below, the output voltage can drop accordingly from the programmed output 0.1 1 LOAD CURRENT (mA) Figure 3. Efficiency for VOUT = 5V voltage. This mode is called maximum duty cycle drop-out. Table 2. Minimum Input Voltage for Regulated Output VOUT VIN (MINIMUM) 5.0V 6.6V 3.3V 4.5V 2.5V 3.5V 1.8V 3.0V CUSTOMIZING THE BOARD The components built on the board are optimized for a wide input voltage range. The bandwidth can be increased for more specific input voltages such as 12V ±10% or 5V ±10% if desired. Some typical applications with typical input voltage ranges that are smaller than the wide input voltage range of the part are included below. The adjustable feedback resistors allow the output voltage to be customized. For output voltages below 3.0V, the boost diode should be moved from D2 to D3 to provide the minimum boost 3 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502 1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER voltage required for the internal power switch. Make sure that the boost capacitor (C8) has a voltage rating greater than or equal to the output voltage for applications where the boost diode is placed in D2. However, the boost capacitor must have a voltage rating greater than the input voltage whenever the boost diode is placed in position D3. 12V +/-10% 5V @1A Vin LT1767EMS8E Vin C2 2.2uF 25V X7R 1206 Boost U1 C8 0.1uF Vout L1 Vsw CDRH5D18-5R4 Sync /Shdn Ceramic D2 CMDSH-3 R1 FB Vc 31.6k Gnd C3 1.5nF R3 C4 100pF D1 R2 10.0k UPS120 C5 4.7uF 6.3V X5R 0805 Ceramic 4.7k 12V +/-10% 3.3V @1A Vin LT1767EMS8E Vin C2 2.2uF 25V X7R 1206 Boost U1 C8 0.1uF Vout L1 Vsw CDRH4D28-4R7 Sync /Shdn Ceramic D2 CMDSH-3 R1 FB Vc 17.4k Gnd C3 2.2nF R3 C4 100pF D1 R2 10.0k UPS120 C5 4.7uF 6.3V X5R 0805 Ceramic 3.3k 5V +/-10% 2.5V @1A Vin D3 CMDSH-3 LT1767EMS8E Vin C2 2.2uF 10V X5R 0805 Boost U1 L1 Vsw 1008PS-272M Sync /Shdn Ceramic Vout C8 0.1uF R1 FB Vc 1.5nF R3 3.3k 10.7k Gnd C3 C4 100pF D1 UPS120 R2 10.0k C5 4.7uF 6.3V X5R 0805 Ceramic 4 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502 1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER 3-5.5V 1.8V @1A Vin D3 CMDSH-3 LT1767EMS8E Vin C2 2.2uF 10V X5R 0805 Boost U1 L1 Vsw 1008PS-272M Sync /Shdn Ceramic Vout C8 0.1uF R1 FB Vc 1.5nF R3 2.2k 4.99k Gnd C3 C4 100pF D1 UPS120 R2 10.0k C5 4.7uF 6.3V X5R 0805 Ceramic 5 5 5 4 3 2 D3 D D2 CMDSH-3 OPT. Vin C8 0.1uF L1 BOOST 2 VIN 8 SYNC VSW C C1 2.2uF 25V 5 SYNC FB Vout 5V/3.3V@1A Vout 3 CDRH5D18-5R4 E1 C6 TAJ OPT. D CMDSH-3 U1 LT1767EMS8E 1 * 3V-25V 1 E2 R2 6 C7 0805 OPT. 31.6k SHDN GND VC 4 7 C5 Vfb C 100pF OPT. E4 R5 100k OPT. D1 UPS140 C3 6800pF SHDN R1 10.0k C2 10uF 6.3V C4 100pF E5 R3 2.2k GND GND E3 E6 EXPOSED PAD SOLDER TO GROUND B B 2 Vfb Vout JP1 1 3 5.0V 3.3V * VIN MINIMUM A 39.2k VOUT CONTRACT NO. 6.6 5 4.5 3.3 3.5 2.5 DRAWN 3 1.8 CHECKED APPROVALS June Wu DATE 2/12/02 See Quick-Start Guide. ENGINEER Keith S. Tuesday, August 06, 2002 3 TITLE A DESIGNER 4 TECHNOLOGY 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 LT1767EMS8E, 1.25MHz Wide Input Range Step Down DC/DC Converter APPROVED 5 R4 2/12/02 SIZE CAGE CODE DWG NO REV A DC502A SCALE: FILENAME: 2 SHEET 1 1 OF 1 Bill Of Material Demo Bd. #502A Linear Technology Corporation LT1767EMS8E 6/17/2005 Item Qty Reference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 1 1 1 1 0 0 0 1 1 1 0 6 2 1 1 1 1 1 1 0 1 1 C1 C2 C3 C4 C5 (OPT.) C6 (OPT.) C7 (OPT.) C8 D1 D2 D3 (OPT.) E1-E6 JP1,JP2 JP1 L1 R1 R2 R3 R4 R5 (OPT.) U1 Part Description CAP., X7R, 2.2uF, 25V, 10% 1206 CAP., X5R, 10uF, 6.3V, 20% 0805 CAP., X7R, 6800pF, 50V, 20% 0603 CAP., NPO, 100pF, 50V, 10% 0603 CAP., 100pF, 0603 Manufacture / Part # TDK, C3216X7R1E225K TDK, C2010X5R0J106M AVX, 06035C682MAT2A AVX, 06035A101KAT2A CAP., 0805 CAP., X7R, 0.1uF, 16V, 20% 0603 Taiyo Yuden, EMK107BJ104MA Schottky Barrier REC., UPS140 MICROSEMI., UPS140 DIODE, CMDSH-3, SOD-323 CENTRAL SEMI., CMDSH-3 DIODE, CMDSH-3, SOD-323 CENTRAL SEMI., CMDSH-3 TURRET, MILL-MAX 2501-2 0.079 SINGLE ROW HEADER, 3 PIN COMM CON, 2802S-03-G1 SHUNT, COMM CON, CCIJ2MM-138G INDUCTOR, 5.4uH SUMIDA, CDRH5D18-5R4 RES.,CHIP, 10.0K, 1/16W, 5% 0603 AAC, CR16-103JM RES.,CHIP, 31.6K, 1/16W, 1% 0603 AAC, CR16-3162FM RES.,CHIP, 2.2K, 1/16W, 5% 0603 AAC, CR16-222JM RES.,CHIP, 39.2K, 1/16W, 5% 0603 AAC, CR16-3922FM RES., CHIIP 0603 I.C., LT1767EMS8E MS8 Exposed Linear Tech. LT1767EMS8E PRINTED CIRCUIT BOARD DEMO BOARD DC502A Page 1 - of - 1