First, determine what supplies to use for the input and bias rails. A 1.8-V input can be stepped down to 1.5 V at 1.5 A if an external bias is provided, because the maximum dropout voltage is 165 mV if V_BIAS is at least 3.25 V higher than V_OUT. To achieve this voltage step, the bias rail is supplied by the 5-V supply. The approximation in Equation 4 estimates the efficiency at 83.3%.

The output voltage then must be set to 1.5 V. As Table 7-1 describes, set R₁ = 4.12 kΩ and R₂= 4.75 kΩ to obtain the required output voltage. The minimum capacitor sizing is desired to reduce the total solution size footprint; see the Input, Output, and Bias Capacitor Requirements section for C_IN = 1 µF, C_BIAS = 1 µF, and C_OUT = 2.2 µF. Use C_SS = 1 nF for a typical 1.8-ms start-up time.

Figure 7-2 shows a simplified version of the final circuit.