QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799 SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE LTC3442EDE DESCRIPTION Demonstration Circuit 799 is a high efficiency synchronous Buck-Boost converter using the LTC3442. The input range is from 2.4V 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 BuckBoost converters. For 2.7V minimum input voltage, this converter can provide up to 1.2A load current. The output voltage is set at 3.3V. A different output voltage in the range of 2.4V to 5.25V can be obtained by changing one of the feedback resistors. The switching frequency is set at 1MHz, which is a good trade-off between efficiency and size. Adjusting RT can program the frequency between 300kHz to 2MHz. In shutdown, the IC itself draws less than 1A. The LTC3442 has manual or programmable Automatic Burst Mode operation and programmable average input current limit. When using long wire connections to the input source (such as wall adaptors), there can be input over voltage transients during initial plug-in. C2 is installed on DC799 to damp the possible voltage transients. C2 is not needed for any application when the input source is close to the regulator. Please refer to Application Note 88 for details. Design files for this circuit board are available. Call the LTC factory. LTC is a trademark of Linear Technology Corporation Table 1. Performance Summary (TA = 25C unless otherwise noted) PARAMETER CONDITION VALUE Minimum Input Voltage -40C to 85C 2.4V Maximum Input Voltage -40C to 85C 5.5V Output Voltage VOUT VIN = 2.5V to 5.5V, IOUT = 0A to 1.1A 3.3V 4% Maximum Output Current VIN = 2.5V 1.1A Maximum Output Current VIN = 2.7V 1.2A Typical Output Ripple VOUT VIN = 3.6V, IOUT = 1.1A (20MHz BW) 45mVPP Typical Switching Frequency RT=43.2K 1MHz VIN = 4.2V, IOUT = 0.2A 93% Typical VIN = 4.2V, IOUT = 1.0A 90% Typical Off (40C to 85C) 0.4V MAX On (-40C to 85C) 1.4V MIN Efficiency (Fixed Frequency Mode) On/Off Control QUICK START PROCEDURE Demonstration circuit 799 is easy to set up to evaluate the performance of the LTC3442. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799 SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE 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. 2. 3. NOTE: Make RUN JP2 DISABLE JP3 AUTO ON 4. Check for the proper output voltage. Vout = 3.17V to 3.43V. NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 5. With power off, connect the input power supply to Vin and GND. sure that the input voltage does not ex- ceed 5.5V. Place jumpers in the following positions: JP1 Turn on the power at the input. Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other parameters. GRAPHICS Figure 1. Proper Measurement Equipment Setup 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799 SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE GND VIN Figure 2. Measuring Input or Output Ripple Efficiency vs. Load 100% 90% 80% Efficiency% 70% 60% 50% 40% 2.7Vin PWM 30% 3.6Vin PWM 20% 2.7Vin Burst 10% 4.2Vin Burst 4.2Vin PWM 3.6Vin Burst 0% 0.1 1 10 100 1000 10000 Iout (mA) Figure 3. Efficiency of DC799 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799 SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE Figure 4. Load Transient Response (Vin=3.6V; top trace: Vout, 100mV/div; bottom trace: Iout load step: 200mA to 1.2A) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 799 SYNCHRONOUS BUCK-BOOST CONVERTER WITH AUTOMATIC BURST MODE 5