STMicroelectronics LF33CDT-TR

Overview

LF33CDT-TR from STMicroelectronics is a 3.3 V, 500 mA very low-dropout linear regulator with logic-controlled shutdown (TTL-compatible inhibit), ±2% output voltage accuracy at 25 °C, 0.4 V typical dropout at 500 mA, and operation from −40 to 125 °C. It serves as a local power supply in automotive body control modules requiring stable low-noise bias under cold-crank conditions.

For engineers reviewing the LF33CDT-TR datasheet, LF33CDT-TR pinout, LF33CDT-TR application, or LF33CDT-TR equivalent, key selection criteria include dropout voltage at full load, quiescent current in OFF mode (50 µA), thermal performance in DPAK (R_thJA = 100 °C/W), and AEC-Q100 qualification for automotive use.

Technical Context

The LF33CDT-TR implements a PNP pass transistor architecture enabling ultra-low dropout (0.4 V typ. at 500 mA) and high PSRR (80 dB at 120 Hz). Its internal current and thermal limiting protect against fault conditions without external components.

It features a dedicated TTL-compatible inhibit pin (Pin 2) that enables system-level power gating: asserting low disables output while reducing quiescent current to 50 µA, supporting standby modes in battery-sensitive applications.

Key Specifications

Pinout & Package

LF33CDT-TR is housed in a DPAK (TO-252-3) surface-mount package with exposed thermal pad (electrically connected to GND), optimized for automotive thermal cycling reliability and manual rework compatibility.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LDL1133PU33R and TPS78033QDDCRQ1, the LF33CDT-TR delivers optimal balance of automotive qualification, 500 mA capability, and cost-effective DPAK packaging-making it the default choice for mainstream BCM and telematics applications where ±2% tolerance and 0.4 V dropout are sufficient.

Availability

LF33CDT-TR is available at Aetrix Electronics and suitable for automotive body control modules, infotainment power sequencing, ADAS camera ECUs, and telematics control units requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LF33CDT-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 analog, MCU, power, and sensing solutions for automotive, industrial, and consumer markets.

The LFXX series was developed specifically for automotive power management, emphasizing AEC-Q100 compliance, ultra-low dropout, and minimal external components to reduce system cost and board space in space-constrained ECUs.

FAQ

What is the minimum input voltage required for regulation at 500 mA load?

The LF33CDT-TR requires a minimum input voltage of 3.7 V to maintain 3.3 V output at 500 mA, based on its 0.4 V typical dropout voltage. At higher temperatures or worst-case process corners, dropout may reach 0.7 V, so 4.0 V is recommended for robust design margin in automotive applications.

Can the INH pin be left floating, or does it require a pull-up/down resistor?

The INH pin must not be left floating: it has no internal pull-up or pull-down. For default-ON operation, connect INH to IN via a 10 kΩ resistor; for default-OFF, tie INH to GND. Floating INH may cause unpredictable output behavior due to noise susceptibility in automotive environments.

Is the exposed thermal pad on the DPAK package electrically connected, and how should it be routed?

Yes, the exposed thermal pad on the LF33CDT-TR's DPAK package is electrically connected to GND. It must be soldered to a dedicated GND copper pour with ≥4 thermal vias (0.3 mm diameter) to an internal GND plane to achieve specified R_thJA = 100 °C/W and prevent thermal shutdown during sustained 500 mA operation.

Does the LF33CDT-TR require an input capacitor, and if so, what value and type?

Yes-an input capacitor of ≥0.1 µF ceramic (X7R, 10 V rating) is required between IN and GND, placed within 3 mm of the device. This stabilizes the input source impedance and prevents oscillation during fast load transients, especially when powered from long traces or high-ESR bulk capacitors.