DC289A Analog Devices

DC289 Introduction Description Demonstration Circuit DC289 is a step-down (buck) regulator using the LTC 1701. The combination of the LTC1701s tiny SOT-23 package and high switching frequency results in a highly efficient application in a small board space. It is ideal for cell phones and other portable electronics operating from one Li-Ion cell or three to four NiCd or NiMH cells. DC289 operates from a 2.5 to 5.5V input voltage range and is capable of providing 0.5A with a jumper-selectable output voltage of 1.5/2.5/3.3V-ADJ. This board highlights the capabilities of the LTC1701, which uses a current mode, constant off-time architecture to control an internal P-channel power MOSFET at about 1MHz. This high performance power supply occupies less than 0.3 square inches and has low output voltage ripple and fast transient response. At low output currents, the LTC1701 automatically switches to Burst Mode operation to maintain high operating efficiencies by minimizing supply current. The part can be shut down by pulling the I /RUN pin low, further reducing the supply current to less TH than 1A. In dropout, the P-channel MOSFET is turned on continuously (100% duty cycle), providing low dropout operation with V V , thereby maximizing battery life. OUT IN Quick Start Guide Demonstration Board DC289 is easy to set up for evaluation of the LTC1701. Please follow the procedure below for proper operation: 1. Move jumper JP1 to the appropriate position for the required output voltage. For voltages other than the preset value, make sure you install the calculated resistor at the pad provided for R7. 2. To shut down the circuit, connect the I /RUN terminal to ground. When the part is TH not shut down, be careful not to add excessive capacitance to the I /RUN pin, since TH it affects the transient response. 3. Connect the input power supply to the V and GND terminals. IN 4. Connect the load between the V and GND terminals. Refer to the connection OUT diagram (Figure 1) for proper measurement equipment setup. XXXYYYY 0.5A, SOT-23, DC/DC CONVERTER + LTC1701 V IN + + SCOPE + I / TH V OUT RUN JP1 GND + LOAD GND DC289A Figure 1. DC289A Connection Diagram 1.5 2.5 ADJ +