QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913 POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING LTC3773EUHF DESCRIPTION Demonstration circuit 913 is a high efficiency and The critical power components are on the top side of high density supply featuring the 3-output, 3-phase the PC board and are within a 1.7 x 1.7 drop-in synchronous buck regulator LTC3773. The input layout area. The small signal components and IC are voltage range of the demo board is designed for 4.5V on the bottom side of the PC board within a 1 x 1 to 13.5V, though the LTC3773 controller can take up board area. The LTC3773EUHF regulator IC is in a to 36V Vin. The outputs of this board are small 5mm x 7mm QFN package with exposed ther- MAX 2.5V/15A,1.8V/15A and 1.2V/15A. To minimize input mal pad for low thermal impedance. An optional 5V ripple current and capacitor size, there is 120 phase bias supply is stuffed on the board to power the clock interleaving among every two phases. The LTC3773. power up/down tracking of the three output voltages is programmable. The supply can be synchronized Design files for this circuit board are available. to an external clock signal. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Input Voltage Typical 4.5V-13.5V (15V abs max) Output Voltage V I = 0A to 15A 2.5V 2% OUT1 OUT1 Output Voltage V I = 0A to 15A 1.8V 2% OUT2 OUT2 Output Voltage V I = 0A to 15A 1.2V 2% OUT3 OUT3 Maximum Output Current VIN = 4.5V-13.5V 15A Each Output Switching frequency 4.5V-13.5Vin 400kHz Full Load Efficiency V = 12V, V = 2.5V, I = 15A 90% Typical IN OUT1 OUT1 V = 12V, V = 1.8V, I = 15A 88 % Typical IN OUT2 OUT2 V = 12V, V = 1.2V, I = 15A 84.5 % Typical IN OUT3 OUT3 QUICK START PROCEDURE Demonstration circuit 913 is easy to set up to evaluate the performance of the LTC3773EUHF. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 913 POLYPHASE 3-OUTPUT STEP-DOWN SUPPLY WITH TRACKING NOTE: When 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. The following are the default jumper settings: +5V INT 5V PHASMD SDB1 SDB2 SDB3 FC Select INT. ON 120 ON ON ON CCM The following tables show the assembly options to program the power up/down tracking among Vout1, Vout2 and Vout3: VOUT1 TRACKING OPTIONS R8 C13 C10 * 1 Softstart W/O tracking 0 DNP 0.01uF Stuff, value Stuff R, 2 Track TRACK1 TBD value TBD DNP VOUT2 TRACKING OPTIONS R13 R18 C22 1 Softstart W/O tracking DNP DNP 0.01uF 2* Track VOUT1 20K 10K DNP VOUT3 TRACKING OPTIONS R28 R30 C29 1 Softstart W/O tracking DNP DNP 0.01uF 2* Track VOUT2 10K 10K DNP *With existing tracking circuit assembly, VOUT1 starts independently (Option 1). VOUT2 tracks VOUT1 during start up (option 2). VOUT3 tracks VOUT2 during start up (option 2). Figure 6 and 7 are the typical power-up/down waveforms with rail tracking. 4. Check for the proper output voltages: V : 2.45V- OUT1 2.55V, V : 1.764V 1.836V, and V : 1.176V OUT2 OUT3 2. With power off, connect the input power supply to 1.224V VIN and GND. Connect the loads between VOUT1, VOUT2, VOUT3 and GND. Preset the load current NOTE: If there is no output, temporarily disconnect at 0A (minimum). Refer to Figure 1 for correct test the load to make sure that the load is not set too set up. high. 3. Turn on the input power. 5. Once the proper output voltages are established, adjust the loads within the operating range and ob- NOTE: Make sure that the input voltage does not ex- serve the output voltage regulation, ripple voltage, ceed 15V. efficiency and other parameters. 2