ZHCSN49N January 2007 – June 2024
PRODUCTION DATA
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 VBIAS is at least 3.25 V higher than VOUT. 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 CIN = 1 μF, CBIAS = 1 μF, and COUT = 2.2 μF. Use CSS = 1 nF for a typical 1.8-ms start-up time.
Figure 7-2 shows a simplified version of the final circuit.