QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 623 550KHZ MICROPOWER STEP-DOWN DC/DC CONTROLLER LTC3801 DESCRIPTION Demonstration circuit 623 is a step-down (buck) MOSFET in a buck regulator application. The result is regulator, using the LTC 3801 monolithic controller. a high performance power supply that is ideal for cell The DC623 has an input voltage range of 2.5V to 9.8V phones and other portable electronics operating from and is capable of providing 1A at an output voltage of one or two Li-ion cell. Due to the use of surface 2.5V from a single Li-Ion cell. The DC623 highlights mount components, the DC623 is a highly efficient the capabilities of the LTC3801, a constant frequency power supply for use in very small spaces. step-down DC-to-DC controller that comes in a tiny Design files for this circuit board are available. Call the SOT-23 package and runs off extremely low quiescent LTC factory. currents. The LTC3801 uses a current mode PWM LTC is a registered trademark of Linear Technology Corporation. architecture to drive an external P-channel power Table 1. Performance Summary (T = 25C) A PARAMETER CONDITION VALUE Minimum Input Voltage 2.5V Maximum Input Voltage 9.8V Output Voltage V = 2.5V to 9.8V, I = 0A to 1A 2.5V 5% IN OUT Typical Output Ripple V = 4.2V, I = 600mA (20MHz BW) 100mV IN OUT PP Normal V = 4.2V 195 IN Typical Supply Current Sleep V = 4.2V 16 IN V = 4.2V, lth/Run=0V 5 Shutdown IN Maximum Output Current V = 4.2V, V = 2.5V 1A (min) IN OUT Typical Load Regulation V = 4.2V, 100mA I 1A 1% IN OUT QUICK START PROCEDURE Demonstration circuit 623 is easy to set up to evalu- 1. Turn on the input power supply, set to 5V, ate the performance of the LTC3801. Refer to with no load on the output. Measure Figure 1 for proper measurement equipment setup V it should be 2.5V 3% (2.425V to OUT and follow the procedure below: 2.575V). NOTE: When measuring the input or output voltage 2. Vary the load current from no load to 1A. ripple, care must be taken to avoid a long ground lead The output voltage should be within a on the oscilloscope probe. Measure the input or tolerance of 4% (2.4V and 2.6V). output voltage ripple by touching the probe tip directly across the V or V and GND terminals. IN OUT 3. Vary the input voltage from 2.7V to 9.8V. See Figure 2 for proper scope probe technique. The output voltage should be within 5% tolerance (2.375V and 2.625V). 1 GND VIN QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 623 550KHZ MICROPOWER STEP-DOWN DC/DC CONTROLLER 4. With the load current at 1A, measure the 6. To shut down the circuit, connect the RUN output ripple voltage it should measure turret to ground (GND). less than 100 mVAC. When finished, disconnect the power. 5. Observe the voltage waveform at the switch node (pin) the switching frequency should be between 500kHz and 650kHz (T = 2 us and 1.5 us). Figure 1. Proper Measurement Equipment Setup Figure 2. Measuring Input or Output Ripple 2