QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 524 POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER LTC3704 DESCRIPTION Demonstration circuit 524 is a positive input to negative output converter featuring the LTC3704 switching controller. The DC524 converts a 5V–15V input to a –5.2V output and provides up to 2.5A of output current from 5V input. The converter operates at 300kHz with a high efficiency of 89%. The DC524 is set to operate in No RSENSE™ mode with input voltages up to 15V. However, DC524 can be modified for higher input voltages with an optional current sense resistor. The circuit features optional soft-start circuitry that can be enabled or disabled with a single jumper. Also, DC524 has a jumper to program either continuous or Burst Mode™ operation. The DC524 can be synchronized to an external clock of up to 400kHz. Please refer to LTC3704 data sheet for design details and applications information. The DC524 can produce up to 3A from a 5V input source, 4A from 10V source and 5A from 15V source. The actual current capability also depends on the operating temperature and available airflow. As MOSFET Q1 gets hot, its RDS(ON) increases and the available output current decreases. Design files for this circuit board are available. Call the LTC factory. Burst Mode is a registered trademark and No RSENSE is a trademark of Linear Technology Corporation Table 1. Performance Summary PARAMETER CONDITION VALUE Minimum Input Voltage 4.5V Maximum Input Voltage No RSENSE mode 18V (or higher with some modifications) VOUT VIN = 5V to 15V, IOUT1 = 0A to 2.5A –5.2V ±3% Typical Output Ripple VOUT VIN = 5V to 15V, IOUT1 = 0A to 2.5 50mVP–P Nominal Switching Frequency 300kHz QUICK START PROCEDURE Demonstration circuit 524 is easy to set up to evaluate the performance of the LTC3704. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage rip- ple, 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. Place jumper JP1 in the ENABLE position. 2. With power off, connect the input power supply to Vin and GND. Make sure that the input power supply has sufficient current rating at minimum input voltage for the required output load. 3. Turn on the power at the input. NOTE: Make sure that the input voltage does not ex- ceed 15V. 4. Check for the proper output voltage: Vout = –5.2V NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 524 POSITIVE INPUT TO NEGATIVE OUTPUT DC/DC CONVERTER – + + + – – + – OPTIONAL EXTERNAL CLOCK SEE "EXTERNAL CLOCK CONNECTION" SECTION + + LOAD – – – GND Figure 1. Proper Measurement Equipment Setup VIN + Figure 2. Scope Probe Placement for Measuring Input or Output Ripple CONNECTING AN EXTERNAL CLOCK 3. Remove resistor R6. 1. Turn the input power source Off. 4. Install 0Ω resistor R7. 2. Remove the Burst Mode jumper. 3. Set the clock source pulse amplitude to 5V and set the frequency between 330 kHz and 400kHz. 4. Turn the clock source off. 5. Connect the clock source (pulse generator with TTL output) to the middle pin of Burst Mode jumper. 6. Apply input power and observe the switching fre- quency of 300kHz. 7. Turn the clock source on and observe the switching frequency go up to the switching frequency of the external clock. USING AN OPTIONAL CURRENT SENSE RESISTOR MONITORING THE MOSFET CURRENT Monitor the MOSFET current through the Rs1 resistor. 1. Connect a 50Ω coaxial cable across Rs1 with the shield connected to the ground connection of Rs1. 2. Use a 50Ω surface mount resistor to connect the cen- ter conductor of the coaxial cable to the Rs1 terminal which is connected to the source of MOSFET Q1. 3. Set the scope input to 50Ω and connect the coaxial cable to the scope. 4. Set the scope to 5mV/division or less. The current scale with 1mΩ Rs1 and 5mV/div is 10A/div (50Ω resistor at the input of coaxial cable forms 2:1 divider with 50Ω input impedance of scope). 1. Refer to LTC3704 data sheet to determine the proper resistor value. 2. Replace current sense resistor Rs1 with the correct value. 2 5 4 3 2 1 1 2 C 1 RUN 2 ITH VIN 9 3 NFB INTVCC 8 4 FREQ 5 MODE/SYNC 4 D 3 D SENSE 10 GATE 7 C GND 6 B B A A 5 4 3 2 1 Bill Of Material Demo Bd. #524A Linear Technology Corporation LTC3704EMS 6/17/2005 Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 Qty Reference 1 1 1 1 3 1 1 1 1 1 1 2 2 1 1 1 1 1 1 1 1 1 2 1 1 1 0 6 1 4 4 1 2 CC1 CC2 CDC CIN1 CO1,CO2,CO3 CO4 CSS1 CV1 C1 D1 D2 JP1,JP2 XJP1,XJP2 L1 Q1 Q2 RC1 RSS1 RSS2 RS1 RT1 R1 R6,R2 R3 R4 R5 R7 (OPT) TP1-TP6 U1 Part Description CAP., X7R 2200pF 50V 10% CAP., NPO, 100PF, 50V, 10% CAP., X7R 22uF 25V 20% CAP., X5R 47uF 16V 20% CAP., X5R 100uF 6.3V 20% CAP., X5R 47uF 6.3V 20% CAP., X7R, 0.1UF, 16V, 10% CAP., Y5V 4.7uF 10V 80% CAP., X7R 0.1uF 25V 10% Schottky Rect., 40V/8Amp Schottky Diode, Super-Mini Headers, 3 Pins 2mm Ctrs. Shunt, 2 Pins 2mm Ctrs. Dual Inductor, QTR-Pak Mosfet N-Chan., PowerPAK SO-8 XSTR, NPN Small Sig. RES., Chip 20K 0.1W 1% RES., Chip 1K 0.1W 5% RES., Chip 100 Ohms 0.1W 5% RES., Chip 0.001 1W 5% RES., Chip 80.6K 0.1W 1% RES., Chip 274K 0.1W 1% Jumper, Chip 0 0.1W 5% RES., CHIP, 1.24K, 0.1W, 1% RES., CHIP, 4.02K, 0.1W, 1% RES., Chip 133K 0.1W 1% Jumper, Chip O 0.1W 5% Turret, Testpoint I.C., NoRsense DC/DC Controller SCREW, #4-40, 1/4" STANDOFF, #4-40 1/2" PRINTED CIRCUIT BOARD STENCIL Page 1 - of - 1 Manufacture / Part # AVX 08055C222KAT1A AVX 08055A101KAT1A TDK C5750X7R1E226M TDK C5750X5R1C476MT Taiyo Yuden JMK432BJ107MU TDK C4532X5R0J476M AVX 0805YC104KAT2A AVX 0805ZG475ZAT1A AVX 08053C104KAT2A Microsemi UPS840 Central Semi. Corp. CMDSH-3-LTC CommConn Con Inc. 2802S-03G2 CommConn Con Inc. CCIJ2MM-138G BH Electronics 510-1009 Vishay Siliconix Si7884DP Diodes Inc. MMBT3904-7 AAC CR10-2002FM AAC CR10-102JM AAC CR10-101JM Panasonic ERJM1WTJ1M0U AAC CR10-8062FM AAC CR10-2743FM AAC CJ10-000M AAC CR10-1241FM AAC CR10-4021FM AAC CR10-1333FM AAC CJ10-000M Mill Max 2501-2 Linear Tech. Corp. LTC3704EMS ANY MICRO PLASTICS 14HTSP003 DEMO CIRCUIT 524A STENCIL 524A