QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B 1MHZ SYNCHRONOUS BUCK-BOOST LTC3440 DESCRIPTION Demonstration Circuit 425B is a constant-frequency synchronous Buck-Boost converter using the LTC3440. The input range is from 2.5V to 5.5V, making it ideal for single-cell lithium-ion or three-cell NiCd/NiMH battery applications. This converter provides up to 95% efficiency, much higher than traditional Buck-Boost converters. For 2.5V minimum input voltage, this converter can provide up to 500mA load current. The output voltage is set at 3.3V. A different output voltage in the range of 2.5V to 5.5V can be obtained by changing one of the feedback resistors. The fre- quency is set at 1MHz, which is a good trade-off between efficiency and size. The frequency can be modified by changing R6 or by synchronizing to an external clock. In shutdown, the board draws about 2.5µA, where 2µA goes through the 1MΩ pull up resistor (R4) and the IC itself draws less than 1µA. Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation QUICK START GUIDE Refer to Figure 1 for the connection diagram and follow the procedure below: 1. Apply a voltage source to the input of the circuit between the VIN and GND terminals. The circuit will start up at input voltage higher than 2.5V. NOTE Do not apply more than 5.5V to the input. 2. Attach a voltmeter or oscilloscope probe between the VOUT and GND terminals of the circuit to monitor the output. To start the circuit, the shunt at JP1 needs to be put in RUN position. 3. Attach a load to the output. The available output current depends on the input voltage. Figure 1. Proper Measurement Equipment Setup 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B 1MHZ SYNCHRONOUS BUCK-BOOST PERFORMANCE SUMMARY PARAMETER CONDITION VALUE Input Voltage Range 2.5V to 5.5V Maximum Load Current, Min VOUT = 3.3V, VIN = 2.5V 500mA Typical Output Ripple VOUT = 3.3V, IOUT = 500mA 13mVP-P Typical Operating Frequency R6 = 62K 1MHz TYPICAL PERFORMANCE CHARACTERISTICS 100 4.2V EFFICIENCY (%) 90 3.6V 80 3.0V 70 2.7V 60 10 100 LOAD CURRENT (mA) 1000 Figure 2. Efficiency vs. Load Current (without External Schottky Diodes) 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 425B 1MHZ SYNCHRONOUS BUCK-BOOST 3