QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639 1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE LT1977 DESCRIPTION Demonstration circuit 639 is a monolithic step-down DC/DC switching converter featuring the LT(R)1977. The board is optimized for 3.3V output at up to 1A load current for a steady state input voltage range of 4V to about 36V* with input transients up to 60V . Minimum on-time restrictions and 3.3V output may limit the steady state maximum input voltage to 36V before pulse skipping occurs. With its wide input voltage range, 1.5A internal power switch, 100A supply current (at input voltages above 14V), 500kHz switching frequency and thermally enhanced package, the LT1977 is a very versatile and powerful IC for DC/DC converters that require compact space, high efficiency at both heavy and light loads and high input voltage. The LT1977 500kHz switching frequency allows all of the components to be small, surface mount devices. Synchronization with an external clock of up to 700kHz is possible. The current-mode control topology creates fast transient response and good loop stability with a minimum number of external components. The low resistance internal power switch (0.2) achieves high efficiencies of up to 80%. The shutdown pin can be used to program undervoltage lockout or place the part in micropower shutdown, reducing supply current to less than 1A by driving the pin low. Burst ModeTM reduces zero load current to under 100A at most input voltages while maintaining a regulated output. A power good comparator and a timing delay can be used for additional system diagnostics and sequencing. The soft start function reduces inrush current at soft start and output voltage overshoot. An optional Power Good Feedback output terminal can be used to monitor or control power good feedback externally. The LT1977 datasheet gives a complete description of the part, operation and applications information. The datasheet must be read in conjunction with this Quick Start Guide for demonstration circuit 639. In particular, the datasheet section on `Thermal Calculations' is important for estimating whether a given application's combination of input voltage, load current and frequency will cause the LT1977 to exceed it's absolute maximum rated junction temperature. The LT1977 is assembled in a small 16-pin thermally enhanced package with exposed pad where proper board layout is essential for maximum thermal performance. See the datasheet section `Layout Considerations'. Design files for this circuit board are available. Call the LTC factory. LT is a trademark of Linear Technology Corporation QUICK START PROCEDURE Demonstration circuit 639 is easy to set up to evaluate the performance of the LT1977. Refer to Figure 1. for proper measurement equipment setup and follow the procedure below: NOTE: Make sure that the input voltage does not ex- ceed 60V. NOTE: The synchronization, shutdown, and power good functions are optional and their terminals can be left floating (disconnected) if their functions are not being used. NOTE: Do not hot-plug the input voltage terminal VIN. The absolute maximum voltage on VIN is 60V and hot-plugging a power supply through wire leads to the demonstration circuit can cause the voltage on the extremely low-ESR ceramic input capacitor to ring to twice its DC value. This is due to high currents instantaneously generated in the inductive supply leads 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639 1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE from an input voltage step on the low-ESR ceramic input capacitor. A bulky higher-ESR capacitor, and an additional inductive filter can be added to the circuit to dampen hot-plug transient ringing. See Application Note 88 for more details. In order to protect the IC, a transient voltage suppressor diode can be added between VIN and GND terminals to absorb any high voltage transient ringing that may occur due to hotplugging. NOTE: If the output voltage is too low, temporarily disconnect the load to make sure that the load is not set too high. 2. Once the proper output voltages are established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. NOTE: Connect the power supply (with power off), load, and meters as shown in Figure 1. 1. After all connections are made, turn on input power and verify that the output voltage is 3.3V. Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 639 1.5A, 500KHZ STEP-DOWN CONVERTER WITH BURST MODE 3 A B C D E Vin TP1 SHDN SYNC 4 R9 200k TP4 15 U1 LT1977IFE 4 TP2 D2 1N4148W VIN Gnd C3 2.2uF 100V TDK 1812 3 4 + C10 (Opt.) N/C Vin 4V-60V* BOOST SHDN TP5 14 SYNC 10 FB 12 R4 24k R10 0 PG 16 CT C1 330pF BIAS D1 B260A CSS 7 9 8 C2 1500pF C7 0.01uF GND R1 24k Vout VC SW N/C N/C 2 5 1 C8 0.01uF PGFB Vout L1 15uH CDRH6D28-150NC C4 0.1uF 3 11 D4 (Opt.) 6 TP3 + C5 100uF 6.3V AVX D-CASE NIOBIUM 80mOhm R2 165k 1% C6 (Opt.) Vout 3.3V at 1A 3 TP6 Gnd C11 10pF 13 R3 100k 1% R8 100k 1% 2 2 R11 (Opt.) TP7 PGOOD TP8 R12 (Opt.) LTC CONFIDENTIAL - FOR CUSTOMER USE ONLY Customer Notice 1 * Transients Up to 60V, See Quick Start Guide A B 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. This Circuit Is Proprietary To Linear Technology And Supplied For Use With Linear Technology Parts. C PGFB OPTION LINEAR TECHNOLOGY CORPORATION 1630 McCARTHY BLVD. MILPITAS, CA. 95035 408-432-1900 408-434-0507 FAX 1 Title High Voltage 1.5A 500kHz Step-Down Converter with Burst Mode Size Document Number Date: Monday, August 23, 2004 DEMO 639A D Rev LT1977IFE Sheet 1 E of 1 Bill Of Material Demo Bd. #639A Linear Technology Corporation LT1977IFE 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 1 1 1 1 2 1 1 0 1 1 0 1 1 1 2 1 2 0 7 0 1 C11 C1 C2 C3 C7,C8 C4 C5 C6,C10 D1 D2 D4 L1 R10 R2 R3,R8 R9 R1,R4 R11,R12 TP1-TP7 TP8 U1 Part Description CAP., NPO, 10pF, 25V, 5% CAP., NPO , 330pF, 25V, 5% CAP., NPO, 1500pF, 25V, 5% CAP., X7R, 2.2uF, 100V, 10% CAP., X7R, 0.01uF, 16V, 10% CAP., X7R 0.1uF 16V 20% CAP., Niobium 100uF 6.3V D case (OPT) DIODE, chottky Rect., 2.0Amp\60V DIODE, Switching Diode (OPT) INDUCTOR, 15uH RES., Chip 0 RES., Chip 165K 0.06W 1% RES., Chip 100K 0.1W 1% RES., Chip 200K 0.06W 5% RES., Chip 24K 0.06W, 5% (OPT) TURRET, Testpoint (OPT) I.C., Step-Down Reg. Page 1 - of - 1 Manufacture / Part # AVX 06033A100JAT2A AVX 06033A331JAT2A AVX 06033A152JAT2A TDK C4532X7R2A225K AVX O603YC103KAT TAIYO YUDEN EMK107BJ104MA AVX NOSD107M006 DIODES INC. B260A-13 SMA DIODES INC., 1N4148W-7 SOD123 SUMIDA CDRH6D28-150NC AAC CJ06-000M AAC CR16-1653FM AAC CR16-1003FM AAC CR16-204JM AAC CR16-243JM Mill Max 2501-2 Linear Tech. Corp. LT1977IFE ****