DEMO MANUAL DC2110A LT8631 100V, 1A Synchronous Micropower Step-Down Regulator Description 95 Demonstration circuit 2110A is a monolithic step-down 90 converter featuring LT 8631. The demo board is designed 85 for 5V output from a 6.5V to 100V input at 400kHz switch- 80 ing frequency. The wide input range makes it suitable for 75 regulating power from a wide variety of sources, includ- ing automotive, industrial systems and telecom supplies. 70 The LT8631 is a compact, high efficiency synchronous 65 monolithic step-down switching regulator. The power 60 f = 400kHz SW switch, compensation and other necessary circuits are 55 V = 12V IN V = 5V OUT inside of the LT8631 to minimize external components 50 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 and simplify design. LOAD CURRENT (A) DC2110a F01 The LT8631 switching frequency can be programmed Figure 1. LT8631 Efficiency vs Load Current either via oscillator resistor or external clock over a 100kHz to 1MHz range. The SYNC pin on the demo board in Figure 2, the input EMI filter is required and the input is grounded (JP1 at Burst Mode position) by default for voltage should be applied at V turret pin, not V . EMI IN low ripple Burst Mode operation. To synchronize to an The LT8631 data sheet gives a complete description of external clock, move JP1 to SYNC and apply the external the part, operation and application information. The data clock to the SYNC turret. If the pulse-skipping operation sheet must be read in conjunction with this demo manual is required, move JP1 to fixed frequency position. Figure 1 for demo circuit 2110A. The LT8631 is assembled in a shows the efficiency of the circuit at 12V input at the Burst 20-lead TSSOP packages. Proper board layout is essential Mode selection. for maximum thermal and electrical performance. See the The demo board has an EMI filter installed. The EMI per- data sheet sections for details. formance of the board (with EMI filter) is shown in Figure Design files for this circuit board are available at 2. The red line in Figure 2 is CISPR25 Class 5 peak limit. DEMO MANUAL DC2110A Quick s p D Demonstration circuit 2110A is easy to set up to evalu- 4. Turn on the power at the input. ate the performance of the LT8631. Refer to Figure 3 for Make sure that the input voltage does not exceed 100V. proper measurement equipment setup and follow the 5. Check for the proper output voltages (V = 5V). procedure below: OUT NOTE. If there is no output, temporarily disconnect the NOTE. When measuring the input or output voltage ripple, load to make sure that the load is not set too high or is care must be taken to avoid a long ground lead on the shorted. oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the V IN 6. Once the proper output voltage is established, adjust or V and GND terminals. See Figure 4 for the proper OUT the load within the operating ranges and observe the scope technique. output voltage regulation, ripple voltage, efficiency and other parameters. 1. Place JP1 on GND position. 7. An external clock can be added to the SYNC terminal 2. With power off, connect the input power supply to V EMI when SYNC function is used (JP1 on the SYNC posi- and GND. If the EMI/EMC performance is not important, tion). Please ensure that the chosen RT sets the LT8631 the input EMI filter can be bypassed by connecting the switching frequency to 10% below the lowest SYNC input power supply to V and GND. IN frequency. See the data sheet Synchronization section 3. With power off, connect loads from V to GND. OUT for details. Detector: +Peak Polarity: Vertical 50 45 40 35 Data 30 25 Class 5 20 Peak 15 10 5 0 -5 0 100 200 300 400 500 600 700 800 900 1000 Frequency (MHz) Detector: +Peak Polarity: Horizontal 50 45 40 35 Data 30 25 Class 5 20 Peak 15 10 55 00 -5-5 0 100 200 300 400 500 600 700 800 900 1000 Frequency (MHz) Figure 2. LT8631 Demo Circuit DC2110A EMI Performance in CISPR25 Radiated Emission Test (14V Input from V Turret Pin, I = 1A) EMI OUT dc2110af 2 AAmmplitude (dBuV/m) Amplitude (dBuV/m) ure roce tart