QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755 600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER LTC3443 DESCRIPTION Demonstration Circuit 755 is a constant-frequency frequency at the MODE/SYNC pin can also synchronous Buck-Boost converter using the synchronize the switching frequency between LTC3443. The input range is from 2.4V to 5.5V, 690kHz to 1.2MHz. In shutdown, the IC draws making it ideal for single-cell lithium-ion or three- less than 1 A. cell NiCd/NiMH battery applications. This When using long wire connection to the input converter provides up to 95% efficiency, much sources (such as wall adaptors), there can be higher than traditional Buck-Boost converters. For input over voltage transients during initial plug-in. 2.5V minimum input voltage, this converter can C8 is installed on DC755 to damp the possible provide up to 1A load current. voltage transients. C8 is not needed for any The output voltage is set at 3.3V. A different output application when input source is close to the voltage in the range of 2.4V to 5.25V can be regulator. Please refer to Application Note 88 for obtained by changing one of the feedback details. resistors. The switching frequency is set at Design files for this circuit board are available. 600kHz, which is a good trade-off between Call the LTC factory. efficiency and size. Applying twice the desired Table 1. Performance Summary (T = 25C unless otherwise noted) A PARAMETER CONDITION VALUE 2.4V (2.5V minimum input for Minimum Input Voltage -40 C to 85C 1A load) Maximum Input Voltage -40 C to 85C 5.5V Output Voltage V V = 2.5V to 5.5V, I = 0A to 1A 3.3V 4% OUT IN OUT Maximum Output Current V = 2.5V 1A IN 12mV (measured at C5) PP Typical Output Ripple V V = 3.0V, I = 1A (20MHz BW) OUT IN OUT 30mV (measured across TP1 PP and TP2) Typical Switching Frequency 600kHz V = 4.2V, I = 0.2A 95% Typical IN OUT Efficiency (Fixed Frequency Mode) V = 4.2V, I = 1A 91% Typical IN OUT Off (40C to 85C) 0.4V MAX On/Off Control On (-40C to 85C) 1.4V MIN 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 755 600KHZ, 1A SYNCHRONOUS BUCK-BOOST CONVERTER QUICK START PROCEDURE Demonstration circuit 755 is easy to set up to 2. With power off, connect the input power supply evaluate the performance of the LTC3443. Refer to Vin and GND. to Figure 1 for proper measurement equipment 3. Turn on the power at the input. setup and follow the procedure below: NOTE: Make sure that the input voltage does not NOTE: When measuring the input or output voltage exceed 5.5V. ripple, care must be taken to avoid a long ground 4. Check for the proper output voltage. Vout = lead on the oscilloscope probe. Measure the input 3.17V to 3.43V. or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. NOTE: If there is no output, temporarily See Figure 2 for proper scope probe technique. disconnect the load to make sure that the load is not set too high. 1. Place jumpers in the following positions: 5. Once the proper output voltage is established, adjust the load within the operating range and JP1 RUN observe the output voltage regulation, ripple JP2 FIXED FREQ. voltage, efficiency and other parameters. 2