STMicroelectronics STLQ50C33R

Overview

STLQ50C33R from STMicroelectronics is a fixed-output 3.3 V, 50 mA low-dropout linear regulator with 3 µA quiescent current, BiCMOS architecture, and PMOS pass element. It operates from 2.3 V to 12 V input, delivers 200 mV dropout at 25 mA, and is housed in SOT323-5L for space-constrained battery-powered systems such as real-time clock backup and microcontroller core power.

For engineers reviewing the STLQ50C33R datasheet, STLQ50C33R pinout, STLQ50C33R application, or STLQ50C33R equivalent, key selection criteria include ultra-low IQ for multi-year battery life, guaranteed dropout performance across temperature, thermal protection behavior, and compatibility with 1 µF ceramic output capacitors in compact portable designs.

Technical Context

The STLQ50C33R uses a BiCMOS process with integrated PMOS pass transistor and bandgap reference, enabling stable 3.3 V regulation while maintaining 3 µA ground-pin quiescent current across –40 °C to 125 °C. Its internal thermal foldback activates linearly starting at 125 °C and fully disables output near 163 °C.

Unlike NMOS-based LDOs, the PMOS topology eliminates reverse-current risk when VO > VI but requires external protection if reverse conduction must be blocked. The device achieves ±2% output voltage accuracy over temperature and load, with 30 dB supply voltage rejection at 120 Hz and 560 µV_RMS output noise (200 Hz–100 kHz).

Key Specifications

Pinout & Package

SOT323-5L is a 5-terminal, surface-mount plastic package measuring 2.0 × 2.1 × 0.9 mm (max), optimized for high-density PCB layouts in portable electronics. It features exposed pad thermal path capability and JEDEC-compliant tape-and-reel packaging (EIA-481).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-quiescent-current LDO applications.

Compared with XC6206P332MR and AP7361-C33YG-7, the STLQ50C33R uniquely combines 3 µA IQ, integrated thermal foldback, and SOT323-5L size-making it optimal for long-life, space-constrained, thermally unmanaged battery systems where reliability under fault conditions is non-negotiable.

Availability

STLQ50C33R is available at Aetrix Electronics and suitable for portable/battery-powered equipment, electronic sensors, and microcontroller power applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for STLQ50C33R includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing silicon solutions for automotive, industrial, and consumer markets since 1987.

The STLQ50 series belongs to ST's ultra-low-power linear regulator product line, engineered specifically for battery-operated devices demanding multi-year operational life, minimal board area, and robust thermal behavior without external protection circuitry.

FAQ

What is the minimum input voltage required for regulation at 3.3 V output?

The STLQ50C33R maintains regulation down to 2.3 V input, but practical minimum depends on load and temperature. At 25 mA and 25 °C, dropout is 200 mV - so 3.5 V input guarantees stable 3.3 V output. Below 3.5 V, output drops linearly with input until dropout limit is exceeded.

Can STLQ50C33R be used with ceramic output capacitors smaller than 1 µF?

No - the datasheet specifies ≥1 µF ceramic capacitor with ESR < 5 Ω for guaranteed stability (Figure 11). Using smaller values risks oscillation or poor transient response. ST validates stability only with 1 µF or larger; 2.2 µF X7R is commonly used for margin.

Does the ADJ pin require termination on the STLQ50C33R?

No - Pin 1 (ADJ) is internally disconnected on fixed-output versions like STLQ50C33R. It may be left floating or connected to GND for mechanical reinforcement; neither affects regulation, noise, or thermal performance per Table 2 and Figure 3.

How does thermal foldback behave during sustained short-circuit events?

Under short-circuit, output current decreases linearly as junction temperature rises above 125 °C; output voltage follows proportionally. At ~163 °C, VO drops to 0 V. Recovery is automatic upon cooldown - no latch or manual reset required - but sustained shorts still risk exceeding safe operating area if input voltage is high.