Consider the following system power requirements: V_IN = 1.2 V, V_OUT = 0.9 V, I_LOAD = 13.5 A, and the ambient temperature is 85 C. The system noise requirement is 2.45 uV_RMS, we need the PSRR to be at least 45 dB at 500 kHz, and the additional load regulation can be as high as 20 mV. We select the TPS7A57 LDO to be paralleled to meet the high load current specification. We enter these system requirements into the system architecture calculator [reference 5]. As shown in Figure 4-3 we need at least 4 parallel TPS7A57 LDOs to meet these system requirements.

These results do not include PSRR, which must be assessed separately. Upon review of the TPS7A57 data sheet Figure 6-6 (repeated below in Figure 4-3), we must limit the average LDO current to be 4 A maximum to meet the PSRR specification. Thus we need at least 13.5 A / 4 A = 3.375 LDOs or 4 LDOs to meet the PSRR requirement. This is the same result as the number of parallel LDOs needed to meet the other system requirements, therefore the PSRR specification will not change the results in Figure 4-3. If desired, a statistical analysis on V_LOAD and I_OUTn can be completed as discussed in Section 3.