DEMO CIRCUIT 1184A QUICK START GUIDE LTC3860EUH DUAL OUTPUT SYNCHRONOUS BUCK CONVERTER DESCRIPTION Demonstration circuit DC1184A is a dual output voltage The main features of the board are listed below: mode synchronous buck converter featuring the Differential amplifier for remote sensing V OUT1 LTC3860EUH. This board provides two outputs of which is setup for 1.2V. 1.2V/25A and 1.8V/25A from an input voltage of 10V to Optional components for single output dual 14V at a switching frequency of 500kHz. The power phase operation. stage consists of the Renesas R2J20602NP which is a CLKIN pin for synchronization to an external tri-state PWM compatible 8mm x 8mm DrMOS and a clock which can be used in conjunction with 0.47uH 13.2mm x 12.8mm iron powder type inductor optional PHSMD resistors and CLKOUT pin for from Wurth. An on-board 5V LT1616 buck regulator up to 12-phase operation. provides the 5V bias for the LTC3860 and the DrMOS. TRACK/SS pins for external coincident rail tracking. The demo board uses a high density, two sided drop-in RUN pins and PGOOD pins for each phase. layout. The power components, excluding the bulk out- For each phase, optional footprints for an put and input capacitors, fit within a 1.5 x 1.25 area LTC4449 gate driver and two top FETs and two on the top layer. The control circuit resides in a bottom FETs. 0.75 x 0.75 area on the bottom layer. The package style for the LTC3860EUH is a 32-lead 5mm x 5mm Design files for this circuit board are available. Call QFN. the LTC factory. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 10V Maximum Input Voltage 14V I V = 10V to 14V Output Voltage V OUT1 = 0A TO 25A, IN 1.2V 1.75% OUT1 I V = 10V to 14V Output Voltage V = 0A TO 25A, 1.8V 1.75% OUT2 IN OUT2 Nominal Switching Frequency 500kHz V = 1.2V, I = 25A, V = 12V Efficiency 87.8% typical OUT1 OUT1 IN See Figure 2 V = 1.8V, I = 25A, V = 12V 91.0% typical OUT2 OUT2 IN 1 LTC3860EUH QUICK START PROCEDURE Demonstration circuit 1184A is easy to set up to evalu- 4. Once the proper output voltages are estab- ate the performance of the LTC3860EUH. Refer to Fig- lished, adjust the loads within the operating ure 1 for the proper measurement equipment setup and range and observe the output voltage regula- follow the procedure below: tion, ripple voltage, efficiency and other pa- rameters. 1. Place jumpers in the following positions: JP1 RUN1 ON Note 1. Do not apply load between the VOS1+ and JP2 RUN2 ON VOS1- pins or between the VO2+ and VO2- pins. These JP3 INT 5V ON pins are only intended to sense the output voltage JP4 +5V SELECT INT across COUT4 and COUT10 respectively. Heavy load currents applied across these pins may damage the 2. With power off, connect the input power supply converter. to VIN and GND. Turn on the power at the input Note 2. Use J9 and J10 to monitor the output volt- and increase the input voltage to 10V or higher. age ripple. J9 will measure the ripple across COUT2 and 3. Check for the proper output voltages: J10 will measure the ripple across COUT8. Connect J9 Vout1 = 1.179V to 1.221V and J10 to the oscilloscope with a short coaxial cable. Vout2 = 1.769V to 1.832V To avoid excessive noise pickup, keep the length of the cable to a minimum. SINGLE OUTPUT / DUAL PHASE OPERATION A single output / dual phase converter may be preferred 7. Stuff R60 with 0 Ohms to tie the two RUN for high output current applications. The benefits of pins together. single output / dual phase operation is lower ripple cur- 8. Stuff R57 with 0 Ohms to tie the two TRK/SS rent through the input and output capacitors, improved pins together. load step response and simplified thermal design. To 9. Tie VOUT1 to VOUT2 by tying together the implement single output / dual phase operation, make exposed copper pads on the VOUT the following modifications: shapes with pieces of heavy copper foil. 1. Select phase 1 to be the master and phase 2 the slave since the differential amplifier already senses V . OUT1 2. Stuff R16 with 0 Ohms to disable the error amp for phase 2. 3. Stuff 0 Ohms at R49 to tie COMP1 to COMP2 and remove the redundant com- pensation components. 4. Stuff R20 with 0 Ohms. 5. Remove 0 Ohm resistor at R25 to release IAVG from ground. 6. Stuff C16 with 100pF to filter the IAVG signal. 2