DEMO CIRCUIT 1580A QUICK START GUIDE LTC3856EUH HIGH EFFICIENCY POLYPHASE BUCK CONVERTER DESCRIPTION Demonstration circuit 1580A is a high efficiency, The RUN pin (JP1) provides enable feature. To shut polyphase, synchronous buck converter with 4.5V to down the converter, one simple way is to force the 14V input range. It can supply 50A maximum load RUN pin below 1.2V (JP1: OFF). Use JP3 jumper to current at 1.5V output. The demo board uses the select burst mode, stage shedding mode or forced LTC3856EUH controller. The LTC3856 is a fea- continuous mode operation. The phase of CLKOUT ture-rich single-output dual-phase synchronous buck is set by JP2. Switching frequency is pre-set at controller with on-chip drivers, remote output volt- about 400KHz, and it can be easily modified from age sensing. This board is setup with sense resistor 250KHz to 770KHz. Please see LTC3856 data sheet configuration with optional inductor DCR sensing for detailed information. circuit. Temperature compensation function can guarantee accurate current limit over a wide tem- Design files for this circuit board are available. Call perature range with DCR sensing. Stage shedding the LTC factory. function allows the controller to decrease the phase number to be one at the light load condition in order to save switching related loss. Adaptive voltage po- sitioning (AVP) can help improve the transient re- sponse. The LTC3856 is suitable for input from 4.5V to 38V and output up to 5V. The LTC3856 can pro- vide high efficiency, high power density and versatile power solutions for telecom and datacom systems, industrial and medical instruments, DC power distri- bution systems and computer systems. The control- ler is available in 32-pin 5mm 5mm QFN and 38- pin SSOP packages. Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Input Voltage Range 4.5V to 14V Output Voltage, V V = 4.5-14V, I = 0A to 50A 1.5V 2% OUT IN OUT Maximum Output Current, I V = 4.5-14V, V = 1.5V 50A OUT IN OUT Typical Efficiency V = 12V, V = 1.5V, I = 50A IN OUT OUT 87.7% Typical Switching Frequency 400kHz 1 LTC3856EUH QUICK START PROCEDURE Demonstration circuit 1580A is easy to set up to evaluate the performance of the LTC3856EUH. Refer to Figure 1 for the proper measurement equipment setup and follow the procedure below: 1. With power off, connect the input power sup- ply to Vin (4.5V-14V) and GND (input return). 2. Connect the 1.5V output load between Vout and GND (Initial load: no load). 3. Connect the DVMs to the input and outputs. 4. Turn on the input power supply and check for the proper output voltages. Vout should be 1.5V+/-2%. 5. Once the proper output voltages are estab- lished, adjust the loads within the operating range and observe the output voltage regula- tion, ripple voltage and other parameters. Note: When measuring the output or input voltage ripple, do not use the long ground lead on the oscillo- scope probe. See Figure 2 for the proper scope probe technique. Short, stiff leads need to be soldered to the (+) and (-) terminals of an output capacitor. The probes ground ring needs to touch the (-) lead and the probe tip needs to touch the (+) lead. 2