Pity the poor low-dropout regulator (LDO): like the late comic and actor Rodney Dangerfield, it just doesn't get a lot of respect. Designers who should know better automatically assume that the switching DC/DC regulator is the regulator of choice, because "everyone" knows that the LDO is inefficient.
Despite this somewhat-undeserved negative reputation, there are at least 30 credible LDO vendors, offering well over 1000 truly distinct LDOs (not just temperature/performance/package variations of a given model number), and billions are shipped every year in both fairly old and very new designs.
Why the contradiction between LDO image and LDO reality? Depending on the line, load, and usage patterns, the LDO may have overall efficiency comparable to the switcher, or at least "good enough" for the applications. After all, not every application's must-have list is totally dominated with concerns about saving every milliwatt. In exchange, the LDO gives you a lot: simplicity in use, good behavior with various loads, little need for external passives, low noise, good transient response, and more.
Perhaps you are wondering, "What do you specifically mean by that word 'more,' anyway?" It turns out that LDOs can be designed to handle harsh, high-temperature environments and still meet some pretty good specs.
Two recent introductions demonstrate this aspect of LDOs clearly. The TPS7H1101-SP and TPS7H1201-HT LDOs from Texas Instruments (see figure below) deliver up to 3 A and 0.5 A, respectively -- no big deal, so do plenty of other available LDOs. But the 3-A unit is QML Class V qualified for operation up to 125°C, targeting military, satellite, and undersea cable applications; the 0.5-A device is qualified to 210°C, aiming at downhill-drilling needs.
In addition, due to their load-sharing-compatible outputs, each of these LDOs can be paralleled to yield double their individual current outputs, thus reaching 6 A and 1 A (depending on which device you are using). Input range is 1.5 to 7V and dropout is just 75 mV, with output noise of 17 µVrms.
It's not just TI announcing high-temperature LDOs, either. Linear Technology just introduced the LT1965, an adjustable 1-A unit for operation to 150°C, and just 40 µVrms noise (see figure below). This device has an input range of 1.8 to 20 Vdc, and a resistor-settable Vout of 1.9 to 19.5 V, along with 300 mV typical dropout. To counter the bad reputation for low efficiency of LDOs, the regulator also can be put into a shutdown mode for less than 1 µA dissipation.
Before you assume that the LDO is yesterday's solution to today's design problem for tomorrow's products, take a look at the huge assortment of LDOs offered by the many reputable vendors. You may be surprised to find that the virtues of the LDO are what you need, while their apparent primary shortcoming of low efficiency is not as bad you think -- and you may also get high-temperature performance that is harder to achieve, or requires a more complex, and thus costly, switching architecture.