STMicroelectronics L4940P85

Overview

L4940P85 from STMicroelectronics is a fixed-output, very low-dropout linear voltage regulator delivering 8.5 V at up to 1.5 A, featuring 450 mV typical dropout at 1 A, ±2% output voltage accuracy over load/temperature, and integrated reverse polarity protection. It operates with input voltages as low as 9.5 V and supports battery-powered industrial instrumentation requiring stable low-noise 8.5 V rails.

For engineers reviewing the L4940P85 datasheet, L4940P85 pinout, L4940P85 application, or L4940P85 equivalent, this page provides verified technical context, package-specific thermal data, real-world load regulation performance (≤30 mV), and validated alternatives for 8.5 V LDO replacement in embedded power subsystems.

Technical Context

The L4940P85 implements a monolithic PNP-based pass transistor architecture with internal current limiting, antisaturation circuitry, and thermal shutdown activation at +150 °C junction temperature. Its design eliminates external compensation components and enables stable operation with only 0.1 µF input and 22 µF output ceramic capacitors.

It delivers regulated 8.5 V output across input ranges from 9.5 V to 17 V, maintains ≤1.2 mV/°C output drift, and achieves 58–66 dB supply voltage rejection at 120 Hz under 1 A load - confirming suitability for noise-sensitive analog front-ends and microcontroller power domains.

Key Specifications

Pinout & Package

Supplied in TO-220FP package (3-pin, vertical mounting, insulated tab), with pin 1 = Input, pin 2 = Ground, pin 3 = Output. Thermal resistance junction-to-ambient is 60 °C/W, requiring minimum 2 cm² copper pour for 1.5 A continuous operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8.5 V LDO regulator applications.

Compared with TLV1117-85CDR and MCP1703T-8502E/MB, the L4940P85 uniquely combines 1.5 A capability, reverse polarity tolerance, and thermal shutdown in TO-220FP - making it the sole choice for ruggedized 8.5 V power delivery where reliability under fault conditions is mandatory.

Availability

L4940P85 is available at Aetrix Electronics and suitable for portable medical sensors, industrial PLC I/O modules, automotive body control units, and smart meter power management requiring stable component supply and long-term lifecycle support.

Supply support for L4940P85 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 L4940 series belongs to ST's legacy linear regulator product line, engineered specifically for industrial and battery-powered equipment demanding low dropout, high reliability, and integrated fault protection without external components.

FAQ

What is the minimum input voltage required for L4940P85 to maintain regulation at 1.5 A?

The L4940P85 requires a minimum input voltage of 9.0 V to sustain 8.5 V output at 1.5 A, based on its maximum dropout voltage of 900 mV per datasheet Table 5. At 1 A, typical dropout is 450 mV, allowing operation from 8.95 V - but design margin requires ≥9.0 V input under worst-case conditions including temperature and tolerance.

Does L4940P85 require an external heat sink for 1.5 A continuous operation?

Yes - in TO-220FP package with R_thJA = 60 °C/W, dissipating 0.75 W at 1.5 A (ΔV = 0.5 V) raises junction temperature by 45 °C above ambient. With 25 °C ambient, T_J reaches 70 °C - acceptable, but at 70 °C ambient, T_J hits 115 °C. A 10 °C/W heatsink is recommended for full-load operation above 50 °C ambient.

Can L4940P85 be used with ceramic output capacitors only?

Yes - the device is stable with ≥22 µF X7R/X5R ceramic output capacitance and ≥0.1 µF ceramic input capacitance, as confirmed in Figure 6 test circuits and Table 4/5 conditions. No ESR requirements apply, unlike older LDOs, simplifying capacitor selection and reducing board area.

Is L4940P85 qualified for automotive applications?

No - the L4940P85 is not AEC-Q100 qualified and is specified for industrial and consumer use only. While it operates across −40 to +150 °C junction range, ST explicitly states non-automotive grade parts carry no automotive qualification and must be used in automotive systems at the user's own risk per document disclaimer on page 23.