DEMO MANUAL DC1940A Low Quiescent Current, High Voltage Step-Down Converter DESCRIPTION Demonstration circuit 1940A is a low quiescent current, Please note, MOSFETs with higher voltage ratings may af- synchronous buck converter featuring the LTC 3891EUDC. fect the efficiency. If 60V MOSFETs are used, the MOSFET This demo board converts a 16V to 60V voltage to a 12V avalanche rating and testing is typically done with 30% at 15A output. over voltage margin (78V for 60V rated MOSFET). Please check with particular MOSFET manufacturer to ensure the The main features of this board include an internal LDO avalanche voltage rating. for gate drive power from V or EXTV , RUN and IN CC PGOOD pins, a mode selector that allows the converter The DC1940A supports the following MOSFET packages: to run in constant current mode (CCM), pulse-skipping or LFPAK, PowerPAK SO-8 and Power 56. The subsequent Burst Mode operation, and selectable current limit. The logic level (SV gate) MOSFETs can be used with DC1940A. DC1940A supports an adjustable output voltage, soft-start Si7850DP Vishay and tracking. The wide input voltage range of 16V to 60V is RJK0651DPB Renesas suitable for double battery automotive and distributed DC HAT2266H Renesas power systems where low quiescent current is important. BSC100N06LS3 G Infineon The LTC3891 data sheet gives a complete description of FDMS86520L Fairchild this part, operation and application information. The data For synchronization to an external clock, remove jumper sheet must be read in conjunction with this quick start JP2 and apply sync signal on terminal SYNC. guide for demo circuit 1940A. Design files for this circuit board are available at The 60V avalanche rated MOSFETs, which are used DEMO MANUAL DC1940A QUICK START PROCEDURE Demonstration circuit 1940A is easy to set up to evaluate 3. Turn on the power at the input. Check for the proper the performance of the LTC3891EUDC. Refer to Figure 1 output voltages: for proper measurement equipment setup and follow the V = 11.9V to 12.4V OUT1 procedure below: NOTE: If there is no output, temporarily disconnect the NOTE: When measuring the input or output voltage ripple, load to make sure that the load is not set too high. care must be taken to avoid a long ground lead on the 4. Once the proper output voltages are established, adjust oscilloscope probe. Measure the input or output voltage the load within the operating range and observe the ripple by touching the probe tip directly across the V or IN output voltage regulation, ripple voltage, efficiency and V and GND terminals. See Figure 2 for proper scope OUT other parameters. probe technique. 1. Place jumper JP1 in the ON position. 2. With power off, connect the input power supply to V IN and GND. DC1940a F01 Figure 1. Proper Measurement Equipment Setup dc1940af 2