QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 797 1MHZ SYNCHRONOUS BUCK-BOOST IN 3MM X 3MM DFN LTC3440EDD DESCRIPTION Demonstration Circuit 797 is a constant-frequency can be modified by changing R6 or by synchronizing synchronous Buck-Boost converter using the to an external clock. In shutdown, the IC itself draws LTC3440EDD. The input range is from 2.5V to 5.5V, less than 1mA. making it ideal for single-cell Lithium-Ion or three-cell When using long wire connections to the input NiCd/NiMH battery applications. This converter pro- sources (such as wall adaptors), there can be input vides up to 95% efficiency, much higher than tradi- over voltage transients during initial plug-in. C8 is tional Buck-Boost converters. For 2.5V minimum in- installed on DC797 to damp the possible voltage put voltage, this converter can provide up to 540mA transients. C8 is not needed for any application when load current. the input source is close to the regulator. Please refer The output voltage is set at 3.3V. A different output to Application Note 88 for details. voltage in the range of 2.5V to 5.25V can be obtained Design files for this circuit board are available. Call by changing one of the feedback resistors. The the LTC factory. switching frequency is set at 1MHz, which is a good LTC is a trademark of Linear Technology Corporation trade-off between efficiency and size. The frequency Table 1. Performance Summary (T = -40C to 85C unless otherwise noted) A PARAMETER CONDITION VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 5.5V Output Voltage V V = 2.5V to 5.5V, I = 0mA to 540mA 3.3V 4% OUT IN OUT Maximum Output Current V = 2.5V 540mA IN Maximum Output Current V = 2.7V 600mA IN 12mV (measured at C2) PP Typical Output Ripple V V = 2.5V, I = 500mA (20MHz BW) OUT IN OUT 22mV (measured across E4 PP and E5) Typical Switching Frequency 1MHz V = 4.2V, I = 100mA 94% Typical IN OUT Efficiency (Fixed Freq.) V = 4.2V, I = 500mA 91% Typical IN OUT Off 0.4V MAX On/Off Control On 1.5V MIN 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 797 1MHZ SYNCHRONOUS BUCK-BOOST CONVERTER IN 3MM X 3MM DFN QUICK START PROCEDURE Demonstration circuit 797 is easy to set up to evalu- 2. With power off, connect the input power supply to ate the performance of the LTC3440EDD . Refer to Vin and GND. Figure 1 for proper measurement equipment setup 3. Turn on the power at the input. and follow the procedure below: NOTE: Make sure that the input voltage does not ex- NOTE: When measuring the input or output voltage ceed 5.5V. ripple, care must be taken to avoid a long ground lead 4. Check for the proper output voltage. Vout = 3.17V on the oscilloscope probe. Measure the input or out- to 3.43V. put voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See NOTE: If there is no output, temporarily disconnect Figure 2 for proper scope probe technique. 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, ad- just the load within the operating range and ob- JP1 RUN serve the output voltage regulation, ripple voltage, JP2 FIXED FREQ. efficiency and other parameters. 2