STMicroelectronics LDF33PT-TR

Overview

LDF33PT-TR from STMicroelectronics is a 1 A adjustable-output low-dropout linear regulator in DFN6 (3x3) package, operating from 2.6 V to 16 V input, delivering 0.8 V to 12 V output with ±1% precision at 25 °C and ±1.5% over -40 °C to 125 °C, featuring logic-controlled shutdown, Power Good flag, 500 mV max dropout at 1 A, and internal thermal/current protection - used in battery-powered microprocessor power rails.

For engineers reviewing the LDF33PT-TR datasheet, LDF33PT-TR pinout, LDF33PT-TR application, or LDF33PT-TR equivalent, key selection criteria include dropout voltage at full load, PG threshold accuracy, ADJ pin reference voltage stability, quiescent current across temperature, and DFN6 thermal resistance (R_thJA = 55 °C/W).

Technical Context

The LDF33PT-TR implements an adjustable LDO architecture with a precision 0.8 V internal reference, error amplifier feedback via ADJ pin, and open-drain Power Good output triggered at 92% of V_ADJ (rising) and 80% (falling). It uses internal N-channel pass transistor topology enabling fast transient response and low noise.

Its control loop requires external ceramic capacitors (C_IN ≥ 1 μF, C_OUT ≥ 2.2 μF), with stability dependent on ESR range versus C_OUT; enable logic (EN pin) directly controls pass device bias, and shutdown reduces I_q to 30 μA (typ.) at 25 °C.

Key Specifications

Pinout & Package

Package: DFN6 (3x3 mm, 0.9 mm height), exposed thermal pad connected to GND per datasheet Figure 17 and Table 5.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar adjustable LDO regulator applications.

Compared with XC6210B332MR-G and ADM7172ACPZ-3.3-R7, the LDF33PT-TR uniquely combines 1 A adjustability, integrated PG signaling, and DFN6 thermal performance - making it optimal for space-constrained, multi-rail embedded systems requiring sequencing and monitoring.

Availability

LDF33PT-TR is available at Aetrix Electronics and suitable for battery-powered microcontrollers, industrial PLC I/O modules, and medical patient monitoring sensors requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LDF33PT-TR 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, power, and embedded applications.

The LDF series targets high-precision, low-noise, thermally robust LDO regulation for next-generation portable and industrial electronics - emphasizing adjustability, fast transient response, and integrated system-level functions like Power Good.

FAQ

What is the minimum input voltage required for 1.2 V output at 1 A?

The LDF33PT-TR requires VIN ≥ VOUT + VDROP. With VOUT = 1.2 V and max VDROP = 500 mV at 1 A and 125 °C, minimum VIN is 1.7 V. However, datasheet specifies absolute minimum VIN = 2.6 V for guaranteed operation across temperature and process variation - so 2.6 V is the practical lower limit.

Can the ADJ pin be left unconnected for fixed-output use?

No. The ADJ pin must be connected to a resistor divider between VOUT and GND to set output voltage. Leaving it floating violates datasheet requirements and causes undefined regulation. For fixed-output variants, ST offers pin-compatible parts like LDF33PU-TR (3.3 V fixed), not the ADJ version.

How is the Power Good (PG) pin configured externally?

The PG pin is open-drain and requires an external pull-up resistor (10–100 kΩ) to a logic-compatible voltage (e.g., 3.3 V or 5 V). When VOUT is within ±2% of target, PG pulls low; otherwise, it remains high-impedance. No internal pull-up exists - omitting the resistor disables PG functionality.

Does the exposed thermal pad require solder connection to PCB ground?

Yes. Per DS10028 Rev 3 Section 7.1, the exposed pad (EXP PAD) is electrically and thermally connected to GND. It must be soldered to a dedicated PCB thermal pad tied to a solid GND plane to achieve specified R_thJA = 55 °C/W and ensure reliable thermal performance at full 1 A load.