Texas Instruments LM317LZ/LFT7

Overview

LM317LZ/LFT7 from Texas Instruments is a 3-terminal, adjustable positive-voltage linear regulator delivering up to 100mA output current with 1.25V to 37V programmable output voltage range. It uses floating topology, sees only input-to-output differential voltage (max 45V), and requires no output capacitor for stability. It serves as a precision voltage or current regulator in low-power industrial power supplies and analog sensor conditioning circuits.

For engineers reviewing the LM317LZ/LFT7 datasheet, LM317LZ/LFT7 pinout, LM317LZ/LFT7 application, or LM317LZ/LFT7 equivalent, key selection criteria include its 100mA output capability, ±3000V HBM ESD rating, –40°C to +125°C operating junction temperature, 1.25V reference voltage tolerance (±0.036V), and compatibility with TO-92 package layout constraints.

Technical Context

The LM317LZ/LFT7 implements an NPN Darlington output stage with internal 1.25V bandgap reference and feedback amplifier. Its floating architecture enables high-side regulation and operation with input voltages hundreds of volts above ground-provided the VI–VO differential stays within 45V (CSO:RFB). Regulation relies on ADJUST pin current (44–57µA) flowing into the OUTPUT pin, requiring minimum load current (1.28mA typical) to maintain accuracy.

It integrates overcurrent and thermal-overload protection that remains active even if the ADJUST pin is disconnected. Ripple rejection reaches 71.5dB at 120Hz with optional 10µF ADJUST-to-ground capacitor, and line regulation is 0.007%/V typical-enabling stable performance in noisy AC/DC front-end stages and battery-backed systems.

Key Specifications

Pinout & Package

LM317LZ/LFT7 is supplied in TO-92 package (LP variant), with 3 leads: INPUT (pin 1), OUTPUT (pin 2), and ADJUSTMENT (pin 3). The TO-92 form factor (4.8mm × 3.68mm) supports through-hole mounting and manual prototyping, and provides adequate thermal dissipation for ≤500mW continuous operation at ambient temperatures ≤60°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM317LZ/LFT7, LM317LDR2G offers SMT scalability but demands thermal derating, while LM317LZ-AP delivers identical performance in identical TO-92 form - making it the only true footprint-compatible alternative for through-hole upgrades.

Availability

LM317LZ/LFT7 is available at Aetrix Electronics and suitable for solar energy charge control, HVAC sensor power supplies, and optical network terminal units requiring stable component supply with long-lifecycle support and consistent parametric performance.

Supply support for LM317LZ/LFT7 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 power management technologies, with decades of leadership in linear regulator design and industrial-grade reliability.

The LM317L series was developed for cost-sensitive, low-power industrial and telecom applications requiring rugged, adjustable regulation without external compensation - targeting analog sensor interfaces, battery chargers, and distributed power rails.

FAQ

What is the maximum input-to-output differential voltage supported by LM317LZ/LFT7?

The LM317LZ/LFT7 supports a maximum input-to-output differential voltage of 45V, applicable to devices fabricated at the CSO:RFB wafer site. This rating enables safe operation with high-input-voltage sources such as solar arrays or unregulated DC bus rails, provided the differential does not exceed 45V under all operating conditions including transients.

Can LM317LZ/LFT7 be used as a precision current source?

Yes, LM317LZ/LFT7 can function as a precision current source by connecting a single resistor between the ADJUST and OUTPUT pins. The output current equals 1.256V divided by the resistor value (I_OUT = 1.256V / R_SET). With ADJUST pin current drift <2.5µA over temperature, this configuration achieves better than ±1% current accuracy in battery charger and LED bias applications.

Does LM317LZ/LFT7 require an output capacitor for stability?

No, LM317LZ/LFT7 does not require an output capacitor for stability due to its internal compensation and Darlington output stage. An output capacitor (e.g., 1µF) may be added to improve transient response, but it is optional and has no effect on loop stability - simplifying design in space-constrained analog modules where capacitor placement is challenging.

What is the operating junction temperature range for LM317LZ/LFT7?

The LM317LZ/LFT7 is characterized for an operating junction temperature range of –40°C to +125°C. This specification applies to the new chip (CSO:RFB) version and ensures reliable regulation in industrial environments such as HVAC control cabinets, outdoor solar enclosures, and factory-floor instrumentation where ambient temperatures exceed 85°C.

How is the output voltage calculated for LM317LZ/LFT7?

The output voltage of LM317LZ/LFT7 is calculated using V_OUT = 1.256V × (1 + R2/R1) + I_ADJ × R2, where R1 connects OUTPUT to ADJUST, R2 connects ADJUST to ground, and I_ADJ is 44–57µA. Since I_ADJ × R2 contributes <0.5% error for R2 ≤ 10kΩ, the simplified formula V_OUT ≈ 1.256V × (1 + R2/R1) is commonly used in LM317LZ/LFT7 designs.