Select the circuit topology. The cost, space, and efficiency are key concerns in home appliance design, so select a Buck topology. Use a synchronous converter with integrated FET and high switching frequency to reduce the bill of material cost and size.
Then, select the TLV62568/9. The TLV62568/9 is a high efficiency synchronous converter in a SOT563 package, and typically operates at a 1.5-MHz frequency pulse width modulation (PWM) at moderate to heavy load currents. At light load, the device automatically enters Power Save Mode (PSM) to maintain high efficiency.
Next, set the output voltage, which is adjusted by the resistor divider, as shown in Equation 1. A reference design example is for a 1.8-V power supply, when sizing R4, to achieve low current consumption and acceptable noise sensitivity, to use a maximum of 200 kΩ for R4. Larger currents through R4 improve noise sensitivity and output voltage accuracy, but increase current consumption. In this design, 100 kΩ is selected for R4.
A feed forward capacitor, C5 of 6.8 pF, is recommended for improving the loop bandwidth to make a fast transient response.
The inductor and output capacitor together provide a low-pass filter. The inductor peak-to-peak ripple current, peak current, and the RMS current are calculated using Equation 2, Equation 3, and Equation 4.
The inductor saturation current rating must be greater than the calculated peak current, and the RMS or heating current rating must be greater than the calculated RMS current. Use 1.5 MHz for fSW. Ensure the chosen inductor is rated for the peak current of Equation 3 and the RMS current of Equation 4.
For this design, the inductor used is the DFE252010F-2R2M=P2 (2.2 µH), with a peak current rating of 3.3 A and RMS current rating of 2.3 A.
The capacitor value and ESR determines the amount of output voltage ripple. The TLV62568 is intended for use with ceramic or other low-ESR capacitors. Use Equation 5 to determine the required RMS current rating for the output capacitor.
For this design, a Murata 10-µF output capacitor is used.