DEMO CIRCUIT 1312 QUICK START LT3689 GUIDE LT3689 Monolithic 700mA Step-Down Regulator with Power-On Reset and Watchdog Timer DESCRIPTION Demonstration circuit 1312 is a Monolithic 700mA Step-Down Regulator with Power-On Reset and Watchdog Timer featuring the LT3689. The board operates from inputs up to 36V and withstands transients up to 60V. Output is 3.3V, 700mA. When output current is low, the circuit operates in Burst Mode. Users can popular R7 on the EN/UVLO pin to provide a programmable under voltage lockout. Fault protections are provided through power switch current limit, switching frequency fold back and thermal shutdown, etc. abled by JP2. Circuit can be synchronized to an external clock connected to SYNC turret. If SYNC function is used, the Rt resistor should be chosen to set the LT3689 internal switching frequency at least 20% below the lowest synchronization input frequency. The power-on reset and watchdog timer periods are independently adjustable using external capacitors. Tight accuracy specifications and glitch immunity ensure reliable operation of the circuit. Window mode or time out mode is selectable through JP1. Watchdog can be enabled or dis- Design files for this circuit board are available. Call the LTC factory. PERFORMANCE SUMMARY SYMBOL VIN VOUT IOUT IQ EFF TWDU TWDL TRST PARAMETER Input Supply Range Output Voltage Range Output Current No Load Quiescent Current Efficiency Watchdog Upper Boundary Period Watchdog Lower Boundary Period Programmed Reset Period The LT3689 datasheet gives complete descriptions of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for working on or modifying the demo circuit 1327. L, LTC, LTM, LT, Burst Mode are registered trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. Specifications are at TA = 25°C CONDITIONS VOUT=3.3V No load VIN = 12V, IOUT = 700mA C3=10nF C3=10nF C4=10nF MIN 4.5 3.2 0 TYP 3.3 77 82 182 5.88 23 MAX 36 3.4 700 UNITS V V mA uA % ms ms ms 1 LT3689 QUICK START PROCEDURE Demonstration circuit 1312 is easy to set up to evaluate the performance of the LT3689. Refer to 0 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 terminals of the input or output capacitors. See Figure 2 for proper scope probe technique. 1. Place jumpers in the following positions: JP1 T or W (bar) JP2 ON or OFF (When OFF, watchdog disabled) 2. With power off, connect the input power supply to VIN and GND. 3. With power off, connect the load to VOUT and GND. 2 4. Turn on the power at the input. NOTE. Make sure that the input voltage does not exceed 36V. 5. Check for the VOUT=3.3V proper output voltages. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 6. Once the proper output voltage is established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. 7. To test watchdog timer, connect a clock input to the WDI terminal. Observe output at the WDO terminal while the clock parameters are adjusted. 8. To test Power-On reset, observe output at the RESET terminals. LT3689 Figure 1. Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 LT3689 4