Cite the need for a DC-DC voltage regulator, and the first and sometimes only option that comes to mind for many designers is the switching regulator. That makes sense, as switchers are well known for their efficiency—a very important feature in many applications—as well as other virtues.
Nonetheless, the reality is that the classic low-dropout regulator (for some reason, always denoted as LDO, without the noun) is often the better choice, especially for loads below about one-half to one amp. Depending on the specifics of the use case and duty cycle, the LDO may have comparable or even better efficiency than the switcher. The numbers prove this, as billions are used every year, with many LDOs called out in new designs, too.
Besides the efficiency situation, there’s no doubt that LDOs offer advantages with respect to their negligible rail noise, ease of use and design-in, and their function as a “no headache/no hassle” solution to the voltage-regulation problem—in the right setting, of course.
LDOs Simply Voltage Regulation
Recognizing this situation, STMicroelectronics introduced the LDH40 and LDQ40 voltage regulators for automotive and industrial applications. These LDOs start up from an input as low as 3.3 V, operate with up to 40 V applied, and have low quiescent current. Their wide input-voltage range allows for connection to a vehicle’s 12-V bus that can reach up to 40-V transient, to provide power for infotainment systems, instrument clusters, and advanced driver-assistance systems (ADAS).
The LDH40 delivers up to 200 mA and is available in a single version with a user-adjustable output voltage from 1.2 to 22 V. The similar 250-mA LDQ40 is available with a 1.2 -to 12-V adjustable output and a choice of 1.8-, 2.5-, 3.3-, and 5.0-V fixed output voltages (Fig. 1). The devices are stabilized with a small ceramic capacitor on the output.
