DEMO CIRCUIT 1541A QUICK START LT3689 GUIDE LT3694/LT3694-1 36V, 2.6A Monolithic Buck Regulator with Dual LDO DESCRIPTION Demonstration circuit 1541A is an adjustable 2.6A Monolithic Buck Regulator with Dual LDO featuring LT3694/LT3694-1. The buck regulator is capable of generating up to 1.7A at its output while the two LDO regulators are capable of 450mA each. Each regulator has independent track/soft-start circuits simplifying power supply sequencing and interfacing with microcontrollers and DSPs. regulated wall transformers, lead acid batteries and distributed power supplies. The LT3694 can be synchronized to an external clock with the SYNC pin. The LT3694-1 offers a CLKOUT pin allowing other DC/DC converters to synchronize to the LT3694-1 clock. The switching frequency of the board is set to 800kHz. The high switching frequency permits the use of small inductors and ceramic capacitors leading to very small triple output solutions. The constant switching frequency, combined with low impedance ceramic capacitors, results in low, predictable output ripple. The board is robust against outputs shorting to ground fault. The LT3694/LT3694-1 datasheet gives a complete description of the part, operation and application information. The datasheet must be read in conjunction with this quick start guide for demo circuit 1541A. With its wide input voltage range of 4V to 36V, the LT3694/LT3694-1 regulates a broad array of power sources from 4-cell batteries and 5V logic rails to un- The LT3694/LT3694-1 regulator is available in the thermally enhanced low profile 28-lead (4mm × 5mm) UFD and FE packages. Design files for this circuit board are available. Call the LTC factory. L, LTC and LT are registered trademarks of Linear Technology Corporation. VLDO is a trade mark of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. Performance Summary ( TA = 25oC ) PARAMETER Input Voltage Range Output Voltage VOUT1 Output Voltage VOUT2 Output Voltage VOUT3 Output Current IOUT1 Output Current IOUT2 Output Current IOUT3 Switching Frequency VOUT1 Buck Efficiency CONDITIONS VOUT1 = 3.3V, IOUT1 = 1.7A VOUT2 = 2.5V, IOUT2 = 450mA VOUT3 = 1.8V, IOUT3 = 450mA VIN = 12V, IOUT1 = 1.7A VIN = 12V, IOUT2 = 450mA VIN = 12V, IOUT3 = 450mA VIN = 12V, IOUT1 = 1.7A, IOUT2 = 0A, IOUT3 = 0A VALUE 4.5V to 36V 3.3V ± 3% 2.5V ± 3% 1.8V ± 3% 0 to 1.7A 0 to 450mA 0 to 450mA 800kHz ± 10% 85% ± 2% 1 LT3694/LT3694-1 QUICK START PROCEDURE Demonstration circuit 1541A is easy to set up to evaluate the performance of the LT3694/LT3694-1. 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 terminals of the input or output capacitors. See Figure 2 for proper scope probe technique. 1. With power off, connect the input power supply to VIN and GND. Connect loads between output terminals (VOUT1, 2 or 3) and GND. NOTE. Active loads may overload the outputs due to the initial in-rush current. Change to resistive loads if necessary. 2. Turn on the power at the input. 2 NOTE. Make sure that the input voltage does not exceed 36V. NOTE. The input capacitor C2 is a 50V ceramic capacitor. When testing 70V transient protection function on the input, this capacitor may need to be replaced with 100V ceramic capacitors. 3. Check for the proper output voltages. VOUT1=3.3V, VOUT2=2.5V, VOUT3=1.8V NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted. 4. Once the proper output voltage is established, adjust the loads within the operating range and observe the output voltage regulation, efficiency and other parameters. NOTE. Make sure that the power dissipation is limited. LT3694/LT3694-1 Figure 1. Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 LT3694/LT3694-1 4