DEMO CIRCUIT 1695 QUICK START GUIDE LOW QUIESCENT CURRENT, HIGH VOLTAGE STEP-DOWN CONVERTER DESCRIPTION Demonstration circuit 1695 is a Low Quiescent Current, Synchronous Buck Converter featuring the LTC3891EFE. DC1695 converts a 4.5V-60V voltage source to 3.3V at 5.0A. The main features of the board include an internal LDO for power gate driver from VIN or EXTVCC, RUN and PGOOD pins and a Mode selector that allows converter to run in CCM, Pulse Skipping or Burst Mode operation, selectable current limit. DC1695 supports also adjustable output voltage, Soft-Start and Tracking. Synchronization to an external clock is possible as well. The wide input voltage range of 4.5V to 60V is suitable for automotive or other battery fed application and Distributed DC Power Systems where low quiescent current is important. The LTC3891EFE datasheet gives a complete description of this part, operation and application information. The datasheets must be read in conjunction with this quick start guide for demo circuit 1695. The 60V avalanche rated MOSFETs, which are used on DC1695, can be operated at their rated voltage. However, if application derating requirements are stricter, MOSFETs with higher voltage PARAMETER Minimum Input Supply Voltage Maximum Input Supply Voltage Output Voltage Range Typical switching frequency Typical Output Ripple (VOUT, 3.3V) Efficiency Typical (VOUT, 3.3V) Supply Quiescent Current Supply Shutdown Current rating can be used. Please note, MOSFETs with higher voltage ratings may affect the efficiency. If 60V MOSFETs are used, keep in mind that avalanche rating and testing is typically done with 30% over voltage margin (78V for 60V rated MOSFET). Please check with particular MOSFET manufacturer to ensure the avalanche voltage rating. DC1695 supports following MOSFET packages: LFPAK, PowerPAK SO-8 and PowerPAK 1212-8. Subsequent logic level MOSFETs can be used with DC1695 Si7850DP Vishay RJK0651DPB Renesas HAT2266H Renesas BSC100N06LS3 G Infineon Si7120DN Vishay Design files for this circuit board are available. Call the LTC factory. L, LTC, LTM, LT are registered trademarks of Linear Technology Corporation. CONDITIONS VIN = 4.5V to 60V, IOUT1 = 0A to 5A ILOAD = 5.0A Vin=24V; VOUT=3.3V, Io=0A, Burst mode Vin=24V VALUE 4.5 60 3.3±2% 225 40 92 50.8 14.7 UNITS V V V kHz mV % µA µA 1 QUICK START PROCEDURE Demonstration circuit 1695 is easy to set up to evaluate the performance of the LTC3891EFE. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE. When measuring the input or output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the VIN or VOUT and GND terminals. See Figure 2 for proper scope probe technique. 2. With power off, connect the input power supply to VIN and GND. 3. Turn on the power at the input. Check for the proper output voltages VOUT1=3.234V to 3.366V, NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 4. Once the proper output voltages are established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 1. Place jumper JP1 in the ON position: Figure 1. Proper Measurement Equipment Setup GND VIN Measuring Input or output Ripple 2 Efficiency vs Load Curret 100 90 80 70 % 60 50 40 30 20 10 0 1.00E-04 1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 A Figure 3. 3.3V Output, Efficiency vs. Load, Burst Mode, Vin 12V 3 4