Consider the following system power requirements: V_IN = 15 V, V_OUT = 12 V, and I_LOAD = 2.5 A. The system noise requirement is 4.67 uV_RMS, we need the PSRR to be at least 50 dB at 1 MHz, and the additional load regulation can be as high as 60 mV. The application requires high reliability and may operate above 125 C in the future, so an extended performance (-EP) device with an operating junction temperature of 150 C is desired. We select the TPS7A47 LDO to be paralleled to meet the mid Vin, high reliability and increased thermal specifications. We enter these system requirements into the system architecture calculator [see reference 5]. As shown in Figure 4-2 we need at least 3 parallel TPS7A47 LDOs to meet these system requirements.

These results do not include PSRR, which must be assessed separately. A review of the TPS7A47 data sheet reveals plenty of margin in the PSRR curves to the system 50 dB requirement at 1 MHz. Thus the PSRR specification will not change the results in Figure 4-2. If desired, a statistical analysis on V_LOAD and I_OUTn can be completed as discussed in Section 3.

Figure 4-2 Parallel LDO System Requirement Analysis using the TPS7A47 LDO