DEMO CIRCUIT 1695 QUICK START GUIDE LOW QUIESCENT CURRENT, HIGH VOLTAGE STEP-DOWN CONVERTER DESCRIPTION Demonstration circuit 1695 is a Low Quiescent rating can be used. Please note, MOSFETs with Current, Synchronous Buck Converter featuring higher voltage ratings may affect the efficiency. If the LTC3891EFE. DC1695 converts a 4.5V-60V 60V MOSFETs are used, keep in mind that ava- voltage source to 3.3V at 5.0A. lanche rating and testing is typically done with 30% over voltage margin (78V for 60V rated MOSFET). The main features of the board include an internal Please check with particular MOSFET manufac- LDO for power gate driver from VIN or EXTVCC, turer to ensure the avalanche voltage rating. RUN and PGOOD pins and a Mode selector that allows converter to run in CCM, Pulse Skipping or DC1695 supports following MOSFET packages: Burst Mode operation, selectable current limit. LFPAK, PowerPAK SO-8 and PowerPAK 1212-8. DC1695 supports also adjustable output voltage, Subsequent logic level MOSFETs can be used Soft-Start and Tracking. Synchronization to an ex- with DC1695 ternal clock is possible as well. The wide input volt- Si7850DP Vishay age range of 4.5V to 60V is suitable for automotive RJK0651DPB Renesas or other battery fed application and Distributed DC Power Systems where low quiescent current is HAT2266H Renesas important. BSC100N06LS3 G Infineon The LTC3891EFE datasheet gives a complete de- Si7120DN Vishay scription of this part, operation and application in- formation. The datasheets must be read in con- junction with this quick start guide for demo circuit Design files for this circuit board are available. 1695. Call the LTC factory. The 60V avalanche rated MOSFETs, which are L, LTC, LTM, LT are registered trademarks of Linear Technology Corporation. used on DC1695, can be operated at their rated voltage. However, if application derating require- ments are stricter, MOSFETs with higher voltage PARAMETER CONDITIONS VALUE UNITS Minimum Input Supply Voltage 4.5 V Maximum Input Supply Voltage 60 V Output Voltage Range VIN = 4.5V to 60V, IOUT1 = 0A to 5A 3.32% V Typical switching frequency 225 kHz Typical Output Ripple (VOUT, 3.3V) I = 5.0A 40 mV LOAD Efficiency Typical (VOUT, 3.3V) 92 % Supply Quiescent Current Vin=24V VOUT=3.3V, Io=0A, Burst mode 50.8 A Supply Shutdown Current Vin=24V 14.7 A 1 GND VIN QUICK START PROCEDURE Demonstration circuit 1695 is easy to set up to 2. With power off, connect the input power sup- evaluate the performance of the LTC3891EFE. ply to VIN and GND. Refer to Figure 1 for proper measurement equip- 3. Turn on the power at the input. Check for the ment setup and follow the procedure below: proper output voltages NOTE. When measuring the input or output voltage ripple, care VOUT1=3.234V to 3.366V, must be taken to avoid a long ground lead on the oscilloscope NOTE. If there is no output, temporarily disconnect the load to probe. Measure the input or output voltage ripple by touching the make sure that the load is not set too high. probe tip directly across the VIN or VOUT and GND terminals. See Figure 2 for proper scope probe technique. 4. Once the proper output voltages are estab- 1. Place jumper JP1 in the ON position: lished, adjust the load within the operating range and observe the output voltage regula- tion, ripple voltage, efficiency and other pa- rameters. Figure 1. Proper Measurement Equipment Setup Measuring Input or output Ripple 2