8.1.2 Output Regulation With IN Pin Floating

The TPS720 supports a novel feature in which the output of the LDO regulates under light loads when the IN pin is left floating. Under normal conditions, when the IN pin is connected to a power source, the BIAS pin draws only tens of milliamperes. However, when the IN pin is floating, an innovative circuit is used that allows a maximum current of 500 μA to be drawn by the load through the BIAS pin, while maintaining the output in regulation. This feature is particularly useful in power-saving applications where a DC-DC converter connected to the IN pin is disabled, but the LDO is required to regulate the output voltage to a light load.

Figure 27 shows an application example where a microcontroller is not turned off (to maintain the state of the internal memory), but where the regulated supply (shown as the TPS62xxx) is turned off to reduce power. In this case, the TPS720 BIAS pin provides sufficient load current to maintain a regulated voltage to the microcontroller.

Figure 27. Example of Floating IN Pin Regulation