STMicroelectronics LDFM33PUR

Overview

LDFM33PUR from STMicroelectronics is a 3.3 V fixed-output, 500 mA very low dropout linear regulator in DFN6-3x3 package, featuring 1% output accuracy, 300 mV max dropout at 500 mA, 200 µA typical quiescent current, logic-controlled enable (EN), and open-drain Power Good (PG) output - designed for stable voltage regulation in space-constrained, low-noise microprocessor and memory power rails.

For engineers reviewing the LDFM33PUR datasheet, LDFM33PUR pinout, LDFM33PUR application, or LDFM33PUR equivalent, this page delivers verified electrical specs, thermal behavior, EN/PG interface timing, stability requirements for 2.2 µF ceramic output capacitors, and real-world load/line transient response data per DS9220 Rev 7.

Technical Context

The LDFM33PUR employs a PMOS pass transistor architecture enabling ultra-low dropout operation down to 125 mV (typ.) at 500 mA across -40 °C to 125 °C junction temperature. Its internal error amplifier references a precision 0.8 V bandgap, delivering ±1% initial accuracy and ±1.5% over full temperature/load range.

It integrates active protection circuitry including thermal shutdown (170 °C with 10 °C hysteresis), current limiting (~0.8 A short-circuit), and logic-controlled shutdown via EN pin (0.8 V low, 2 V high thresholds). The PG output asserts high when VOUT reaches 92% of nominal and deasserts at 80%, requiring an external pull-up resistor (10–100 kΩ).

Key Specifications

Pinout & Package

Package: DFN6-3x3 mm, 0.4 mm pitch, exposed thermal pad (GND-connected) - optimized for thermal performance and PCB area efficiency in compact designs.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-dropout linear regulator applications.

Compared with TSM117-3.3 and TPS7A2033PDBVR, the LDFM33PUR uniquely balances ultra-low dropout, integrated PG signaling, and robust thermal performance in a production-ready DFN6-3x3 package - making it optimal for applications demanding both precision sequencing and sustained 500 mA delivery under thermal stress.

Availability

LDFM33PUR is available at Aetrix Electronics and suitable for industrial PLC I/O modules, portable medical sensor hubs, laptop embedded controllers, and automotive infotainment display interfaces requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LDFM33PUR 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 microcontrollers, power management ICs, sensors, and analog devices for industrial, automotive, and consumer markets.

The LDFM series was developed specifically for high-precision, low-noise, low-dropout regulation in space-constrained embedded systems - targeting applications where dynamic load response, thermal resilience, and power-good sequencing are critical.

FAQ

What is the minimum input voltage required for LDFM33PUR to maintain regulation at 500 mA?

The minimum input voltage is 3.6 V: 3.3 V output plus maximum dropout of 300 mV. At 25 °C and 500 mA load, typical dropout is 125 mV, so 3.425 V suffices. Below -40 °C or above 125 °C, dropout increases - design margin should include worst-case 300 mV.

Can the PG pin drive a standard CMOS input directly without a pull-up resistor?

No - the PG pin is open-drain and requires an external pull-up resistor (10–100 kΩ) to a valid logic rail (e.g., 3.3 V or 5 V). Without it, PG remains floating and cannot assert a valid high-level signal for sequencing or fault detection.

Is the ADJ pin on LDFM33PUR required to be terminated, and if so, how?

No - the ADJ pin is not connected internally on the fixed-output LDFM33PUR variant (per Table 1 and ordering code table). It must be left unconnected (NC); tying it to any voltage risks leakage current or instability due to internal floating node coupling.

What is the recommended PCB layout practice for the exposed thermal pad on the DFN6-3x3 package?

The exposed pad must be soldered to a solid GND copper pour covering ≥80% of its area, with ≥4 thermal vias (0.3 mm diameter) connecting to inner/ground planes. This achieves the specified R_thJA = 55 °C/W and prevents thermal shutdown under 500 mA continuous load.