DEMO CIRCUIT 999A LTC3533 QUICK START GUIDE LTC3533 3.3V, 1.5A Synchronous Buck- Boost Converter DESCRIPTION Demonstration circuit 999A is a wide input range, 3.3V, Synchronous rectification helps to attain efficiency up 1.5A Synchronous Buck-Boost Converterfeaturing the to 94%, depending on line and load. The LTC3533 LTC3533. provides current limit and shutdown disconnect. It offers Burst Mode operation for high efficiency at light This circuit was designed to demonstrate the high lev- loads. els of performance, efficiency, and small solution size attainable using this part in a buck-boost power sup- Design files for this circuit board are available. Call ply. It operates at 1.0MHz and produces a regulated the LTC factory. 3.3V, 1.5A output from an input voltage range of 2.4 , LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered to 5.5V, and operates down to 1.8V with de-rated out- trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy put current. It is suitable for portable applications, and Drive, FilterCAD, Hot Swap, LinearView, Module, Micropower SwitcherCAD, Multimode Dimming, No Latency , No Latency Delta-Sigma, No R , Operational Filter, PanelProtect, SENSE has a footprint area that is 0.25 square inches. PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT, UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names may be trademarks of the companies that manufacture the products. PERFORMANCE SUMMARY Specifications are at TA = 25C SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS V Input Supply Range 1.8 5.5 V IN V Output Voltage 3.3 V OUT I Output Current Range V = 2.4 5.5V 0 1.5 A OUT IN I Maximum Output Current V = 0.8V (linear interpolation from 0.8 2.4V) 0.8 A OUT IN F Switching (Clock) Frequency 1.0 MHz SW V Output Ripple V = 4.2V, I = 1.5A (20MHz BW) 20 mV OUT P-P IN OUT PP I Output Regulation Line and Load (1.8-5.5V, 0-1.5A) 0.4 % REG P /P Efficiency (see Figure 2) V =4.2V, I = 1.5A 89 % OUT IN IN OUT OPERATING PRINCIPLES The LTC3533 Synchronous Buck-Boost Converter is range. It seamlessly transitions from buck, to buck- employed to produce a 3.3V output from an input boost, to boost modes of operation to maintain the ranging from 1.8V to 5.5V. output as the input voltage goes from maximum to minimum values. The converter utilizes a proprietary 4-switch topology to provide an output that is within the input voltage 1 LTC3533 QUICK START PROCEDURE NOTE. Make sure that the input voltage never exceeds 5.5V. Demonstration circuit 999 is easy to set up to evaluate the performance of the LTC3533. Refer to Figure 1 for 4. Check for the proper output voltage of 3.3V. Turn proper measurement equipment setup and follow the off the power at the input. procedure below: 5. Once the proper output voltages are established, NOTE. When measuring the output voltage ripple, care must be taken to connect a variable load capable of sinking 1.5A at avoid a long ground lead on the oscilloscope probe. Measure the output 3.3V to the output terminals +Vout and Vout. Set voltage ripple by touching the probe tip and ground ring directly across the last output capacitor (COUT) as shown in Figure 1. the current for 0A. 1. Set an input power supply that is capable of 1.8V to a. If efficiency measurements are desired, an am- 5.5V to 4.2V. Turn off the supply. meter or a resistor shunt that is capable of han- dling 1.5Adc can be put in series with the out- 2. With power off, connect the supply to the input put load in order to measure the DC999As out- terminals +Vin and Vin. put current. a. Input voltages lower than 1.8V can keep the b. A voltmeter with a capability of measuring at converter from turning on due to the undervolt- least 3.3V can be placed across the output ter- age lockout feature of the LTC3533. minals in order to get an accurate output volt- b. If efficiency measurements are desired, an am- age measurement. meter capable of measuring 3Adc or a resistor 6. Turn on the power at the input. shunt can be put in series with the input supply in order to measure the DC999As input current. NOTE. If there is no output, temporarily disconnect the load to make sure that the load is not set too high. c. A voltmeter with a capability of measuring at least 5.5V can be placed across the input termi- 7. Once the proper output voltage is again estab- nals in order to get an accurate input voltage lished, adjust the load within the operating range measurement. and observe the output voltage regulation, ripple voltage, efficiency and other desired parameters. 3. Turn on the power at the input. 2