The TPS742 family of devices offers industry-leading dropout performance, making this family well-suited for high-current low V_IN/low V_OUT applications. The extremely low dropout of the TPS742 allows the device to be used in place of a DC-DC converter and still achieve good efficiency. This efficiency allows the user to rethink the power architecture of applications to achieve the smallest, simplest, and lowest cost solution.

There are two different specifications for dropout voltage with the TPS742 devices. The first specification (illustrated in Figure 7-1) is referred to as V_IN Dropout, and is for users who wish to apply an external bias voltage to achieve low dropout. This specification assumes that V_BIAS is at least 1.62 V above V_OUT, which is the case for V_BIAS when powered by a 3.3-V rail with 5% tolerance and with V_OUT = 1.5 V. If V_BIAS is higher than 3.3 V × 0.95 or V_OUT is less than 1.5 V, V_IN dropout is less than specified.

Figure 7-1 Typical Application of the TPS742 Using an Auxiliary Bias Rail

The second specification (shown in Figure 7-2) is referred to as V_BIAS Dropout, and is for users who wish to tie IN and BIAS together. This option allows the device to be used in applications where an auxiliary bias voltage is not available or low dropout is not required. Dropout is limited by BIAS in these applications because V_BIAS provides the gate drive to the pass FET and therefore must be 1.4 V above V_OUT. Because of this usage, IN and BIAS tied together easily consume huge power. Pay attention not to exceed the power rating of the IC package.

Figure 7-2 Typical Application of the TPS742 Without an Auxiliary Bias