Texas Instruments LM317LCPWE4

Overview

LM317LCPWE4 from Texas Instruments is a 100mA adjustable floating linear voltage regulator in TSSOP-8 package, delivering output voltages from 1.25V to 37V with ±5mV/V output regulation and 71.5dB ripple rejection at 120Hz. It operates across –40°C to +125°C junction temperature and requires only two external resistors for programming - used in HVAC control modules and optical network terminal power supplies.

For engineers reviewing the LM317LCPWE4 datasheet, LM317LCPWE4 pinout, LM317LCPWE4 application, or LM317LCPWE4 equivalent, key selection criteria include input-to-output differential voltage tolerance (up to 37V), adjustment pin current (44–57µA), thermal performance in TSSOP (R_θJA = 149.4°C/W), and compatibility with high-voltage floating topologies requiring no output capacitor for stability.

Technical Context

The LM317LCPWE4 implements a floating NPN Darlington output stage that regulates by maintaining a precise 1.25V reference between OUTPUT and ADJUST pins - enabling operation with input voltages hundreds of volts above ground as long as the VI–VO differential stays within 37V. Its feedback architecture inherently supports both voltage and current regulation modes using passive external components.

It integrates overcurrent and thermal-overload protection that remains active even if the ADJUST pin is disconnected. The device draws minimal bias current (44–57µA) into the ADJUST terminal, which must be sunk by the feedback network or load to maintain regulation - a critical design constraint confirmed across all CSO:RFB silicon revisions.

Key Specifications

Pinout & Package

TSSOP-8 (PW) package: 3mm × 6.4mm body, exposed thermal pad, surface-mount compatible. Pin 1 is INPUT; Pins 2, 3, 4, 6 are internally connected OUTPUT; Pin 4 is ADJUSTMENT; Pins 2, 3, 5, 7, 8 are NC (no internal connection) - TI recommends grounding NC pins for improved thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317LDR2G, the LM317LCPWE4 offers lower thermal resistance in compact TSSOP packaging and superior high-voltage floating operation; compared with TLV1117-33CDCYR, it provides full adjustability and 37V differential tolerance but requires external resistors and has lower output current.

Availability

LM317LCPWE4 is available at Aetrix Electronics and suitable for HVAC system power supplies, optical network terminal units (ONT), and analog input modules requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LM317LCPWE4 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and connectivity technologies - serving industrial, automotive, and communications markets with high-reliability components.

The LM317L series is part of TI's legacy linear regulator portfolio designed for robust, low-cost, and easy-to-use voltage regulation in industrial control, energy infrastructure, and telecom power systems - emphasizing floating operation and minimal external component count.

FAQ

What is the maximum input-to-output differential voltage supported by the LM317LCPWE4?

The LM317LCPWE4 supports a maximum input-to-output differential voltage of 37V across its full operating temperature range (–40°C to +125°C). This specification applies to the new chip revision (CSO:RFB) and enables use in high-side floating configurations where the input may be several hundred volts above ground - provided the VI–VO difference does not exceed 37V. Exceeding this rating risks permanent damage.

Does the LM317LCPWE4 require an output capacitor for stability?

No, the LM317LCPWE4 does not require an output capacitor for stability - a key design advantage confirmed in TI's official datasheet. An optional 1µF output capacitor may be added to improve transient response, but it is not necessary for loop stability. This simplifies layout and reduces bill-of-materials cost in space-constrained applications like ONT power supplies.

How is the output voltage calculated for the LM317LCPWE4?

The output voltage of the LM317LCPWE4 is calculated using V_OUT = 1.25V × (1 + R2/R1) + I_ADJ × R2, where R1 connects OUTPUT to ADJUST, R2 connects ADJUST to ground, and I_ADJ is the adjustment pin current (44–57µA for LM317LCPWE4). For most designs, the I_ADJ × R2 term is negligible if R2 ≤ 10kΩ, yielding V_OUT ≈ 1.25V × (1 + R2/R1).

Can the LM317LCPWE4 be used as a precision current regulator?

Yes, the LM317LCPWE4 can be configured as a precision current regulator by connecting a single resistor R_SET between OUTPUT and ADJUST - where I_OUT = 1.25V / R_SET. This exploits the device's fixed 1.25V reference between OUTPUT and ADJUST pins. For example, a 25Ω resistor delivers 50mA output current. The LM317LCPWE4 maintains this current over input voltage variations and load changes within its 100mA rating.

What is the purpose of grounding the NC pins on the LM317LCPWE4 TSSOP package?

Grounding the NC (no-connect) pins on the LM317LCPWE4 TSSOP-8 package improves thermal performance by providing additional conductive paths from the die to the PCB ground plane - reducing junction-to-board thermal resistance (Ψ_JB). TI explicitly recommends this practice in the datasheet to enhance reliability under sustained 100mA load conditions, especially in thermally constrained industrial enclosures.