L78L18ACUTR

Overview

The L78L18ACUTR is a three-terminal positive linear voltage regulator from the STMicroelectronics L78L series, housed in an SOT-89 surface-mount package. It provides a fixed output voltage of 18 V with a maximum output current of 100 mA. The device supports a DC input voltage range up to 40 V and operates within a junction temperature range of 0 °C to 125 °C. Electrical characteristics include a typical quiescent current of 6.5 mA, line regulation of 320 mV, load regulation of 170 mV, and a typical power supply rejection ratio (PSRR) of 38 dB at 120 Hz.

Feature Summary

• Integrates internal current limiting and thermal shutdown protection mechanisms for robust operation under fault conditions.
• Functions as a direct replacement for Zener diode and resistor combinations, offering improved stability and lower noise.
• Requires no external components for basic fixed-voltage regulation applications.

Applications

• Local or on-card voltage regulation
• Elimination of noise and distribution problems associated with single-point regulation
• Replacement for Zener diode/resistor combinations

Procurement Notes

Verify that the component matches the specific L78L18ACUTR designation, ensuring the 'A' suffix indicates ±4% output voltage tolerance and the 'TR' suffix denotes tape-and-reel packaging. Confirm the SOT-89 package type aligns with board layout requirements. Cross-reference the manufacturer part number against official STMicroelectronics documentation to ensure authenticity and correct revision status before procurement.

Selection Notes

Select this regulator when a fixed 18 V output is required with currents up to 100 mA in a compact surface-mount form factor. Ensure the input voltage remains within the 40 V maximum limit and consider thermal dissipation capabilities given the SOT-89 package's thermal resistance. Verify that the ±4% voltage accuracy meets circuit tolerances compared to the standard ±8% option.

Part Context

This component belongs to the L78Lxx series of three-terminal positive regulators designed for low-power applications. The series offers various fixed output voltages ranging from 3.3 V to 24 V. The L78L18 variant specifically targets circuits requiring an 18 V rail, utilizing the same internal architecture as other members in the family while differing only in the internal reference voltage setting.

Replacement Considerations

Direct pin-compatible substitutes within the L78L series include L78L18AU (TO-92), L78L18ASO (SO-8), and L78L18AB/AC variants with different temperature grades. Other manufacturers' equivalents such as LM78L18 may require verification of pinout and electrical parameter alignment.