ZHCSO39B May 2022 – August 2022 TPS7A74
PRODUCTION DATA
First, determine what supplies to use for the input and bias rails. A 2.1-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 180 mV if VBIAS is at least 2.8 V higher than VOUT. To achieve this voltage step, the bias rail is supplied by the 5-V supply. The approximation in Equation 6 estimates the efficiency at 83.3%.
The output voltage then must be set to 1.5 V. As Table 8-1 describes, set R1 = 4.99 kΩ and R2 = 3.82 kΩ to obtain the required output voltage. The minimum capacitor sizing requires the total solution size footprint to be reduced; see the Section 8.1.2 section for CIN = 1 µF, CBIAS = 1 µF, and COUT = 2.2 µF. Use CSS = 1 nF for a typical 0.032-ms start-up time.
Figure 8-2 shows a simplified version of the final circuit.