DEMO MANUAL DC1822B LTC3861EUHE High Current, Dual Output Synchronous Buck Converter DESCRIPTION Demonstration circuit 1822B is a dual output synchro- The main features of the board are: nous buck converter featuring the LTC 3861EUHE. The Remote sensing for each output, where the divider board provides two outputs of 1.5V/25A and 1.2V/25A is placed before a high input impedance differential from an input voltage of 7V to 14V at a switching fre- amplifier. quency of 500kHz. The power stage consists of a 6mm CLKIN and CLKOUT pins. 6mm DrMOS and a 13mm 13mm iron powder type inductor. An on-board 5V LT 3470 buck regulator pro- Optional resistors to tie the two outputs together. vides the 5V bias for the LTC3861 and the DrMOS. Connector and header to tie two or more boards The demo board uses a high density, two sided drop-in together for up to 12-phase operation. layout. The power components, excluding the bulk output Optional footprint for an LTC4449 gate driver and and input capacitors, fit within a 1.5 1.2 area on the discrete MOSFETs. top layer. The control circuit fits in a 1.1 1.0 area on the bottom layer. The package style for the LTC3861EUHE Optional footprint for a dual phase Delta power block. is a 36-lead 5mm 6mm QFN. Design files for this circuit board are available. All registered trademarks and trademarks are the property of their respective owners. PERFORMANCE SUMMARY (T = 25C), no airflow A PARAMETER CONDITION VALUE Minimum Input Voltage 7V Maximum Input Voltage 14V Output Voltage V I = 0A to 25A, V = 7V to 14V 1.5V 2% OUT1 OUT1 IN Output Voltage V I = 0A to 25A, V = 7V to 14V 1.2V 2% OUT2 OUT2 IN V Maximum Output Current, I V = 7V to 14V, V = 1.5V 25A OUT1 OUT1 IN OUT1 V Maximum Output Current, I V = 7V to 14V, V = 1.2V 25A OUT2 OUT2 IN OUT2 Nominal Switching Frequency 500kHz Efficiency V = 1.5V, I = 25A, V = 12V 91.6% Typical OUT1 OUT1 IN (See Figure2 and Figure3) V = 1.2V, I = 25A, V = 12V 90.7% Typical OUT2 OUT2 IN Note: The DC1828B demo circuit and manual replaces the DC1828A. The demo board was modified slightly. Rev 0 1DEMO MANUAL DC1822B QUICK START PROCEDURE Demonstration circuit 1822B is easy to set up to evaluate 3. Next, apply 25A load to each output and re-measure the performance of the LTC3861EUHE. Please refer to VOUT. Figure1 for proper measurement equipment setup and 4. Once the DC regulation is confirmed, observe the out- follow the procedure below. put voltage ripple, load step response, efficiency and 1. With power off, connect the input supply, load and other parameters. meters, as shown in Figure1. Preset the load to 0A NOTE 1. Use the BNC connectors labeled VOUT1 or and V supply to be 0V. Place jumpers in the following IN VOUT2 to measure the output voltage ripple. positions: NOTE 2. Do not apply the load from the VOS1+ turret to JP1 RUN1 ON the VOS1 turret or from the VOS2+ turret to the VOS2 JP2 RUN2 ON turret. These are connected to the sense traces for the output voltage. Heavy load currents applied across these JP3 INT BIAS ON turrets may damage these traces. 2. Adjust the input voltage to be between 7V to 14V. VOUT1 should be 1.5V 2%.VOUT2 should be 1.2V 2%. + + V V OUT1 OUT2 LOAD LOAD A A I I OUT1 OUT2 Monitor voltage across C OUT5 and C for accurate OUT10 efciency measurements. + + V V V V OUT1 OUT2 * * + V V IN dc1822b F01 A I IN + V SUPPLY IN Figure1. Proper Measurement Equipment Setup Rev 0 2