STMicroelectronics LM317MDT-TR

Overview

LM317MDT-TR from STMicroelectronics is a monolithic adjustable positive-voltage linear regulator in DPAK (TO-252) package, delivering up to 500 mA output current with 1.2 V to 37 V adjustable output range, ±0.7% output voltage temperature stability, and integrated thermal overload and short-circuit protection - used in industrial power supplies, lab bench adapters, and programmable DC sources.

For engineers reviewing the LM317MDT-TR datasheet, LM317MDT-TR pinout, LM317MDT-TR application, or LM317MDT-TR equivalent, key selection criteria include input-to-output differential voltage limit (40 V), adjustment pin current (≤100 µA), load regulation (≤25 mV for VO ≤5 V), and junction temperature range (0 °C to 125 °C).

Technical Context

The LM317MDT-TR implements a floating architecture where regulation depends solely on the input-to-output differential voltage (VI–VO), enabling high-voltage applications without ground-referenced constraints. Its internal 1.25 V reference is stabilized across temperature and line/load variations.

It uses external resistor divider feedback (R1/R2) to set output voltage per VO = 1.25 V × (1 + R2/R1) + I_ADJR2, with I_ADJ tightly controlled at 50–100 µA and minimal drift (ΔI_ADJ ≤ 5 µA), ensuring predictable output accuracy and low minimum load current (3.5–10 mA).

Key Specifications

Pinout & Package

DPAK (TO-252) surface-mount package with exposed thermal pad (pin 2), optimized for PCB copper area heat dissipation; R_thJA = 100 °C/W (standard layout), R_thJC = 8 °C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317LDT-TR, the LM317MDT-TR delivers 5× higher current in a thermally superior DPAK package; versus TLV1117-33CDR, it offers full 1.2–37 V adjustability and robust high-voltage operation but requires external resistors and has higher dropout.

Availability

LM317MDT-TR is available at Aetrix Electronics and suitable for industrial power supplies, programmable lab equipment, LED driver modules, and remote sensor biasing requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LM317MDT-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, power, microcontroller, and sensor solutions for industrial, automotive, and consumer markets.

The LM317 series belongs to ST's legacy linear regulator product line, engineered for reliability in harsh environments and ease of use in field-serviceable power systems - emphasizing simplicity, thermal robustness, and wide operating margins.

FAQ

What is the minimum load current required for stable regulation?

The LM317MDT-TR requires a minimum load current of 3.5 mA (typ.) to maintain regulation, rising to 10 mA at maximum VI–VO (40 V). This is due to internal quiescent current returning to the output pin; insufficient load causes output voltage to rise uncontrollably. A 360 Ω resistor from OUTPUT to GND satisfies this requirement for 1.25 V reference compliance.

Can the LM317MDT-TR be used in a high-side floating configuration?

Yes - its floating architecture means it regulates based only on the voltage difference between INPUT and OUTPUT pins. It can be placed between any two nodes (e.g., across a 48 V bus) as long as VI–VO ≤ 40 V and thermal limits are observed. No ground reference is needed at the IC itself, enabling high-side or negative-rail applications with proper external protection diodes.

How does the adjustment pin current affect output accuracy?

I_ADJ (50–100 µA, max 100 µA) flows through R2 in the feedback divider, adding an error term I_ADJ×R2 to the ideal VO = 1.25 V × (1 + R2/R1). For R2 = 10 kΩ, this contributes up to 1.0 V error - so R2 is typically kept ≤1 kΩ, making the error ≤100 mV and easily compensated via R1 scaling.

What thermal considerations apply when using the DPAK package?

The DPAK package has R_thJC = 8 °C/W and R_thJA = 100 °C/W on standard FR-4. To sustain 500 mA at 30 V dropout (15 W dissipation), ≥10 cm² of 2-oz copper connected to the exposed pad is required to keep T_J ≤125 °C at 50 °C ambient. Thermal vias under the pad and inner-layer copper pours significantly improve performance.