QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1171A SYNCHRONOUS BUCK CONVERTER LTC3851EGN DESCRIPTION Demonstration circuit 1171A is a single output synchronous buck converter featuring the LTC3851EGN. The circuit is designed with all components on the top side. The package style for the LTC3851EGN is a 16-lead narrow SSOP. Two versions of the board are available. DC1171A-A has an on-board sense resistor for current feedback, while the DC1171A-B is configured with a DCR sense circuit that allows the converter to use the inductor's DCR as the sense element instead of the on-board sense resistor to save cost, board space while improving full load efficiency over 2%. The main features of the board include an internal 5V linear regulator for bias and a Mode selector that allows the converter to run in CCM, pulse skip or Burst Mode operation (requires some minor modification). Synchronization to an external clock is also possible. The input voltage range is 4.5V to 14V. The LTC3851 datasheet gives a complete description of the part, operation and application information and must be read in conjunction with this quick start guide for demo circuit 1171A. Design files for this circuit board are available. Call the LTC factory. Burst Mode is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25C) PARAMETER CONDITION VALUE Input Voltage Range Output Voltage VOUT 4.5V - 14V VIN = 4.5V to 14V, IOUT = 0A to 15A 1.5V 2% Nominal Switching Frequency Efficiency See Figure 3 and 4 for efficiency curves 400kHz 87.3% Typical (A-A) VOUT = 1.5V, IOUT1 = 15A; VIN = 12V 90.0% Typical (A-B) QUICK START PROCEDURE Demonstration circuit 1171A is easy to set up to evaluate the performance of the LTC3851EGN. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. 1. NOTE: When Place jumpers in the following positions: JP1 400k JP2 On JP3 CCM 2. With power off, connect the input power supply to Vin and GND. 3. Turn on the power at the input. NOTE: Make sure that the input voltage does not exceed 14V. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1171A SYNCHRONOUS BUCK CONVERTER 4. 5. range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. Check for the proper output voltage. Vout = 1.470V to 1.530V NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 6. Once the proper output voltages are established, adjust the loads within the operating Different operating modes can be evaluated by changing the position of jumper JP3 and are discussed in the next section. Iin A + V Vin - + Vin supply - Vout + Iout V - A + Vout load - Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1171A SYNCHRONOUS BUCK CONVERTER GND VIN Figure 2. Measuring Input or Output Ripple Across Terminals or Directly Across Bulk Capacitor FREQUENCY SYNCHRONIZATION AND MODE SELECTION Demonstration circuit 1171A's Mode selector allows the converter to run in CCM or pulse skip operation by changing position of jumper JP3. For synchronizing to an external clock source Table 2. both JP1 and JP3 needs to be adjusted, while for Burst Mode operation some bench modification is needed. Refer to Table 2 and to the data sheet for more details. Mode Selection and Synchronized Operation Options BOARD MODIFICATION MODE SELECTOR CONFIGURATION JP1 JP4 CCM operation - `400K' `CCM' Pulse skip operation - `400K' `P.S.' Burst Mode operation 100k resistor between JP4 pin1 and pin2 `400K' Remove Jumper - `EXTCLK' `BURST' Synchronized to ext. clock applied to MODE/PLLIN pin RAIL TRACKING Demonstration circuit 1171A is configured for an on board soft start circuit. The soft start ramp rate can be adjusted by changing the value of C24. Demonstration circuit 1171A can also be Table 3. modified to track an external reference. Refer to Table 3 for tracking options and to the data sheet for more details. Output Tracking Options TRK/SS RESISTORS AND CAPACITOR RAIL TRACKING CONFIGURATION R32 R35 C24 TRK/SS PIN Soft Start Without Tracking (Default) 0 Open 0.1F Open Vout equals External Ramp 0 Open Open External reference applied Open External reference applied Vout tracking scaled external ramp Resistor divider 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1171A SYNCHRONOUS BUCK CONVERTER Figure 3. Typical Efficiency vs. Load Current for DC1171A-A Figure 4. Typical Efficiency vs. Load Current for DC1171A-B Figure 5. Thermal image of DC1171A-A, 14Vin, 1.5V@15Aout 4 5 4 3 2 1 REVISION HISTORY This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts. Customer Notice: 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 Applications Engineering for assistance. ECO REV DESCRIPTION DATE 3 PROTO 09/25/07 3.1 CHANGED C21, C22, R31, U1 12/02/10 APPROVED DING L. D D E4 E5 MODE/PLLIN VIN FREQ/PLLFLTR C20 400K 0.1uF 10V RUN ON 3 JP1 VIN 1nF R31 C22 1K 3 4.5V-14V + CIN1 150uF 35V R30 OFF 1 J1 C21 EXTCLK 2 1 10nF J2 Q1 RJK0305DPB 5 5 JP2 E1 2 82.5K 1% CIN4 10uF 25V RUN C23 4 INTVCC CIN3 10uF 25V GND E6 4 GND MODE/PLLIN OPT 4 R32 VOUT 1 2 3 1uF 3 E2 2 JP3 C19 1 2 3 1 U1 LTC3851AEGN 0.1uF 10V 2 R35 3 4 OPT 5 6 C26 2200pF 7 C28 330pF R40 6.8K 1% R38 49.9K 1% C29 C32 20pF OPT R39 43.2K 1% C30 8 MODE/PLLIN SW FREQ/PLLFLTR TG RUN BOOST TK/SS VIN ITH INTVCC FB BG SENSE- GND SENSE+ ILIM 15 14 13 R37 10 1 2 12 INTVCC INTVCC R42 VOUT 0 5 5 Q4 OPT VIN 0.68uH COUT3 47uF 6.3V + COUT1 330uF 4V GND E8 GND R27 [1] 10 C27 2.2uF 10V 9 C31 4.7uF 10V R28 R29 [1] C18 [1] OPT B R41 0 R10 [1] R9 [1] [1] CONTRACT NO. APPROVALS DESC RSNSE R9, R10 R27 R29 C18 R43 DRAWN MI DATE 10/10/01 TECHNOLOGY -A RSENSE 3m OHM 10 OHM -B DCR SENSE 10 AWG WIRE DO NOT STUFF DO NOT STUFF DO NOT STUFF DO NOT STUFF DO NOT STUFF 30.1K 1% 0.1uF 50V X7R 0 OHM A SCH, LTC3851AEGN, SYNCHRONOUS BUCK RSENSE / DCR SENSE CONVERTER APPROVED ENGINEER 3.01K 1% SIZE CAGE CODE DESIGNER B Friday, March 04, 2011 4 3 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 TITLE CHECKED 5 1.5V/15A J4 IN DASHED BOX KEEP PARTS CLOSE INTVCC [1] ASSY + COUT2 330uF 4V 11 R43 A C VOUT [1] D1 B340A 4 0 1000pF B 4 D2 CMDSH-3 R36 Q3 RJK0301DPB 1 16 INTVCC 2 1 2 1 C25 0.1uF 10V 1 2 3 0 C24 SW J3 RSNSE 1 2 3 TRK/SS E7 VOUT L1 ILIM C Q2 OPT CCM BURST P.S. SCALE:NONE 2 DWG NO REV 3.1 DC1171A FILENAME: 1171A-3.1.DSN SHEET 1 1 OF 1