LT3506A AND LT3506 DEMO CIRCUIT 958 LT3506A and LT3506 Dual Monolithic 1.6A StepDown Switching Regulator DESCRIPTION Demonstration circuit 958 is a Dual Monolithic 1.6A Step-Down Switching Regulator featuring the LT3506A and LT3506. The top half of the board features the LT3506A circuit. The bottom half of the board features the LT3506 circuit. These two circuits are totally independent on the demo board. The main difference between the two circuits is the switching frequency. The switching frequency of the LT3506A circuit is 1.1MHz. The LT3506 switching frequency is 575KHz. Higher switching frequency allows smaller components in a given application. Lower switching frequency gives higher efficiency and allows a circuit to operate at a lower duty cycle. The LT3506A circuit takes a 6.8V to 25V input and generates a 5V and a 3.3V output, both at 1.6A. The LT3506 circuit takes a 3.6V to 21V input and generates a 1.8V and a 1.2V output, both at 1.6A. The wide input voltage of the LT3506A and the LT3506, 3.6V to 25V, accepts a variety of power PERFORMANCE SUMMARY SYMBOL VIN VIN VOUT1 VOUT2 VOUT3 VOUT4 IOUT VRIPPLE η PARAMETER Input Supply Range Input Supply Range Output Voltage Range Output Voltage Range Output Voltage Range Output Voltage Range Output Current Switching Frequency Switching Frequency Output Ripple Efficiency η Efficiency F F sources, from lead-acid batteries and 5V rails to unregulated wall adapters and distributed power supplies. The output voltage of both the LT3506A and LT3506 can be as low as 0.8V. The LT3506 high switching frequency and current mode control allow the use of small, low profile surface mount components. The circuit is stable with ceramic capacitors. The low ESR of a ceramic capacitor and high switching frequency results in very low, predictable output ripple. The LT3506 datasheet gives complete description 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 958. Design files for this circuit board are available. Call the LTC factory. LT is registered trademark of Linear Technology Specifications are at TA = 25°C CONDITIONS LT3506A Circuit (TOP) LT3506 Circuit (BOTTOM) LT3506A Circuit (TOP) LT3506A Circuit (TOP) LT3506 Circuit (BOTTOM) LT3506 Circuit (BOTTOM) Each Output LT3506A Circuit (TOP), IOUT = 1.6A LT3506 Circuit (BOTTOM), IOUT = 1.6A Each Output, VIN = 12V, IOUT = 1.6A LT3506A Circuit (TOP), VIN = 6.8V, IOUT1 = 0.9A, IOUT2 = 0.9A LT3506 Circuit (BOTTOM), VIN = 3.6V, IOUT3 = 0.9A, IOUT4 = 0.9A MIN 6.8 3.6 4.85 3.2 1.746 1.164 TYP 5 3.3 1.8 1.2 1100 575 15 86.5 78 MAX 25 21 5.15 3.4 1.854 1.236 1.6 UNITS V V V V V V A KHz KHz mV % % 1 LT3506A AND LT3506 QUICK START PROCEDURE Demonstration circuit 958 is easy to set up to evaluate the performance of the LT3506A and LT3506. 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. 1. With power off, connect a 6.8V–25V or a 3.6V21V input power supply to the VIN and the GND terminals on the board corresponding to the top circuit or the bottom circuit. Each circuit is powered separately from its own VIN and GND. 2. Turn on the power at the input. 3. Check for the proper output voltages. VOUT1 = 5V, VOUT2 = 3.3V, VOUT3 = 1.8V, VOUT4 = 1.2V NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 4. The RUN/SS and the Power Good functions are optional and their terminals can be left floating (disconnected) if their functions are not being used. Connecting a RUN/SS terminal to GND will disable the corresponding output. 5. Once the proper output voltages are established, adjust the loads within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. NOTE. Make sure that the input voltage does not exceed 25V. 2 LT3506A AND LT3506 Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 LT3506A AND LT3506 4 LT3506A AND LT3506 5