DEMO CIRCUIT 1541A LT3689 QUICK START GUIDE LT3694/LT3694-1 36V, 2.6A Monolithic Buck Regulator with Dual LDO DESCRIPTION Demonstration circuit 1541A is an adjustable 2.6A regulated wall transformers, lead acid batteries and dis- Monolithic Buck Regulator with Dual LDO featuring tributed power supplies. The LT3694 can be synchro- LT3694/LT3694-1. The buck regulator is capable of gen- nized to an external clock with the SYNC pin. The erating up to 1.7A at its output while the two LDO regula- LT3694-1 offers a CLKOUT pin allowing other DC/DC tors are capable of 450mA each. Each regulator has in- converters to synchronize to the LT3694-1 clock. dependent track/soft-start circuits simplifying power The LT3694/LT3694-1 regulator is available in the ther- supply sequencing and interfacing with microcontrollers mally enhanced low profile 28-lead (4mm 5mm) UFD and DSPs. and FE packages. The switching frequency of the board is set to 800kHz. The LT3694/LT3694-1 datasheet gives a complete de- The high switching frequency permits the use of small scription of the part, operation and application informa- inductors and ceramic capacitors leading to very small tion. The datasheet must be read in conjunction with this triple output solutions. The constant switching frequency, quick start guide for demo circuit 1541A. combined with low impedance ceramic capacitors, re- Design files for this circuit board are available. Call sults in low, predictable output ripple. The board is ro- the LTC factory. bust against outputs shorting to ground fault. L, LTC and LT are registered trademarks of Linear Technology Corporation. VLDO is a trade With its wide input voltage range of 4V to 36V, the mark of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. LT3694/LT3694-1 regulates a broad array of power sources from 4-cell batteries and 5V logic rails to un- o Performance Summary ( T = 25 C ) A PARAMETER CONDITIONS VALUE Input Voltage Range V = 3.3V, I = 1.7A 4.5V to 36V OUT1 OUT1 V = 2.5V, I = 450mA OUT2 OUT2 V = 1.8V, I = 450mA OUT3 OUT3 Output Voltage V V = 12V, I = 1.7A 3.3V 3% OUT1 IN OUT1 Output Voltage V V = 12V, I = 450mA 2.5V 3% OUT2 IN OUT2 Output Voltage V V = 12V, I = 450mA 1.8V 3% OUT3 IN OUT3 Output Current I 0 to 1.7A OUT1 Output Current I 0 to 450mA OUT2 Output Current I 0 to 450mA OUT3 Switching Frequency 800kHz 10% V Buck Efficiency V = 12V, I = 1.7A, 85% 2% OUT1 IN OUT1 I = 0A, I = 0A OUT2 OUT3 1 LT3694/LT3694-1 QUICK START PROCEDURE NOTE. Make sure that the input voltage does not exceed 36V. Demonstration circuit 1541A is easy to set up to evaluate the performance of the LT3694/LT3694-1. Refer to Fig- NOTE. The input capacitor C2 is a 50V ceramic capacitor. When testing 70V transient protection function on the input, this capacitor may need ure 1 for proper measurement equipment setup and fol- to be replaced with 100V ceramic capacitors. low the procedure below: 3. Check for the proper output voltages. 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 VOUT1=3.3V, VOUT2=2.5V, VOUT3=1.8V 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 NOTE. If there is no output, temporarily disconnect the load to make probe technique. sure that the load is not set too high or is shorted. 1. With power off, connect the input power supply to 4. Once the proper output voltage is established, adjust VIN and GND. Connect loads between output termi- the loads within the operating range and observe the nals (VOUT1, 2 or 3) and GND. output voltage regulation, efficiency and other pa- rameters. NOTE. Active loads may overload the outputs due to the initial in-rush current. Change to resistive loads if necessary. NOTE. Make sure that the power dissipation is limited. 2. Turn on the power at the input. 2