onsemi MC33275ST-3T3G 3V LDO Voltage Regulator: Datasheet, Pinout, and Application Circuits
In the realm of power management, Low-Dropout (LDO) regulators are fundamental components for providing clean, stable, and precise voltage rails from a higher input source. The onsemi MC33275ST-3T3G is a robust example of such a device, designed to deliver a fixed 3.3V output at currents up to 250 mA. This article delves into its key specifications, pinout configuration, and typical application circuits.
Datasheet Overview and Key Features
The MC33275 series is renowned for its low dropout voltage and very low ground current, making it ideal for battery-powered applications where efficiency is paramount. The MC33275ST-3T3G is the 3.3V output version in a SOT-223 package.
Critical specifications from its datasheet include:
Output Voltage: Fixed at 3.3V (with a tolerance of ±2% over line, load, and temperature).
Maximum Output Current: 250 mA.
Dropout Voltage: Typically 200 mV at 100 mA load, ensuring operation even when the input voltage dips very close to the output level.
Low Quiescent Current: Features a very low ground current of typically 0.5 mA, which only slightly increases under dropout conditions. This is crucial for extending battery life.
Protection Features: Includes built-in overcurrent protection and thermal shutdown, safeguarding the regulator and the downstream circuitry from damage.
Low Noise Output: By bypassing the reference pin with a small capacitor, output noise can be significantly reduced, benefiting noise-sensitive applications like RF modules and audio circuits.
Pinout Configuration
The MC33275ST-3T3G comes in a 3+1 tab SOT-223 package. The pinout is as follows:
Pin 1 (Input): This pin connects to the input voltage source (VIN). A ceramic input capacitor is required for stability.
Pin 2 (Ground): The common ground connection for the regulator.
Pin 3 (Output): The regulated 3.3V output (VOUT). An output capacitor is required between this pin and ground.
Tab (Output): The large tab is internally connected to Pin 3 (Output). It provides both an electrical connection and a path for heat dissipation. It must be soldered to a copper pour on the PCB to act as a heatsink.
Application Circuits
The basic application circuit for the MC33275ST-3T3G is straightforward, requiring only two external capacitors for stable operation.
1. Standard Regulation Circuit:
The most common setup involves placing a 1.0 µF or greater ceramic capacitor on the input pin (to ground) and a 1.0 µF or greater ceramic capacitor on the output pin (to ground). These capacitors should be located as close as possible to the regulator's pins to ensure stability and good transient response. This circuit is the workhorse for powering microcontrollers, sensors, and other digital ICs.
2. Low-Noise Configuration:
For applications requiring an exceptionally clean voltage rail, such as for analog-to-digital converters (ADCs) or voltage-controlled oscillators (VCOs), the noise performance can be improved. A 10 nF bypass capacitor can be added from the BP (Bypass) pin (available on some variants; check datasheet) to ground. If no dedicated BP pin exists, selecting a higher-quality output capacitor (like a low-ESR tantalum or ceramic) will help.
3. Enable Control Circuit (for Adjustable Versions):
Note that the fixed-voltage MC33275ST-3T3G does not feature an enable pin. However, other variants in the family do. For those, a simple logic-high or logic-low signal applied to the enable pin can turn the regulator output on or off, facilitating power sequencing and sleep modes in portable devices.
The onsemi MC33275ST-3T3G is a highly reliable and efficient 3.3V LDO regulator perfect for a vast array of applications. Its combination of low dropout voltage, low quiescent current, and integrated protection makes it an excellent choice for powering modern electronic devices, particularly those running from batteries. Its simple design-in process, requiring minimal external components, allows for a compact and cost-effective power solution.
Keywords: LDO Regulator, 3.3V Output, Low Dropout Voltage, Low Quiescent Current, SOT-223 Package
