Texas Instruments LM615IM

Overview

LM615IM from National Semiconductor is a monolithic quad comparator with integrated adjustable shunt voltage reference, operating from 4V to 36V supply, featuring open-collector outputs, input common-mode range extending to Vb, and reference output programmable from 1.24V to 6.3V with ±0.6% initial accuracy at 25°C - used in precision power supply monitoring and multi-threshold detection circuits.

For engineers reviewing the LM615IM datasheet, LM615IM pinout, LM615IM application, or LM615IM equivalent, this device serves as a space-saving Super-Block™ alternative to discrete comparator + reference solutions, requiring attention to VRO/FEEDBACK resistor programming, open-collector pull-up selection, and thermal hysteresis management in industrial sensor interfaces.

Technical Context

The LM615IM integrates four independent comparators with lateral PNP input stages enabling low input bias current (≤35 nA max) and wide differential input voltage tolerance (±36V), while maintaining correct operation even when one input lies outside the common-mode range (Vb to Va–1.8V). Its reference section functions as a three-terminal shunt regulator referenced to the Vb terminal, with cathode voltage swing from ~0.7V below Vb up to 6.3V.

Reference regulation relies on a fixed 1.244V internal bandgap (VR) between VRO and FEEDBACK pins; external resistor networks across VRO–FEEDBACK–Anode set output voltage via Thevenin-equivalent synthesis. The device supports stable operation with capacitive loads up to 1 µF and exhibits low dynamic impedance (<1 Ω at high currents), enabling robust noise filtering in analog thresholding applications.

Key Specifications

Pinout & Package

LM615IM is housed in a 16-pin narrow surface-mount package (NSC M16A), measuring 7.5 mm × 10.2 mm with 0.65 mm lead pitch. Pin 1 is marked by a beveled corner or dot; the package is RoHS-compliant and designed for reflow soldering per JEDEC J-STD-020.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad comparator + reference applications.

Compared with LM615IM, the LM339+TL431 solution offers greater design flexibility but increases layout complexity and thermal drift uncertainty, while TLV3704IPW provides modern low-power performance at the cost of missing on-chip reference and high-voltage capability - making LM615IM uniquely suited for ruggedized 4–36V industrial threshold detection.

Availability

LM615IM is available at Aetrix Electronics and suitable for industrial power supply monitors, RGB sensor interfaces, voltage window detectors, and time-delay generators requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LM615IM 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

National Semiconductor Corporation was a U.S.-based analog semiconductor pioneer, acquired by Texas Instruments in 2011; its legacy products remain widely deployed in industrial and automotive systems.

The LM615IM belongs to National's Super-Block™ family - monolithic mixed-signal ICs engineered to replace multi-chip subsystems in space-constrained, high-reliability industrial controls and instrumentation.

FAQ

What is the maximum supply voltage rating for the LM615IM?

The LM615IM has an absolute maximum supply voltage rating of 36V between Va and Vb pins. Electrical specifications are guaranteed from 4V to 36V, making it suitable for direct connection to unregulated 24V industrial rails. Exceeding 36V risks permanent damage, and operation below 4V may result in undefined comparator behavior or reference instability. Always observe derating guidelines per the datasheet's Absolute Maximum Ratings table when designing for thermal stress or transient conditions.

How do I configure the adjustable reference output of the LM615IM to 5.0V?

To set the LM615IM reference output (VRO) to 5.0V, connect a resistor R1 from VRO to FEEDBACK and R2 from FEEDBACK to Vb (anode). Using the internal 1.244V reference (VR), calculate R1 = VR / I and R2 = R1 × ((VRO / VR) – 1), where I ≥ 32 mA for <0.1% error. For 5.0V output: R1 ≈ 39 kΩ, R2 ≈ 118 kΩ. Ensure FEEDBACK bias current remains negligible versus I - verified by measuring <50 nA at FEEDBACK under operating conditions.

Does the LM615IM support rail-to-rail input operation?

No, the LM615IM does not support rail-to-rail input operation. Its specified input common-mode voltage range is Vb to (Va – 1.8V) over temperature. While one input may exceed Va (up to Va + 32V) if the other remains within range, neither input is guaranteed to function correctly above Va – 1.8V or below Vb. This limitation arises from the lateral PNP input stage architecture and must be accounted for in high-side sensing designs - external resistive dividers or level shifters may be required for signals near Va.

Can unused comparators in the LM615IM be left floating?

No, unused comparators in the LM615IM must not be left floating. Per the datasheet, each unused comparator should have its inverting input and output tied to Vb, and its non-inverting input tied to Va. This configuration prevents unintended oscillation, minimizes supply current, and avoids substrate diode conduction that could disrupt operation of active sections. Leaving inputs unconnected risks erratic output states, increased noise susceptibility, and potential thermal instability due to uncontrolled input bias paths.

What is the purpose of the FEEDBACK pin on the LM615IM?

The FEEDBACK pin on the LM615IM is the reference node for the internal 1.244V bandgap voltage (VR). It enables programmable reference output (VRO) by forming a feedback loop with external resistors - the device regulates the voltage between VRO and FEEDBACK to maintain VR. Unlike a standard op-amp feedback pin, FEEDBACK draws minimal current (<50 nA), allowing high-impedance resistor networks. Its voltage is not user-accessible; instead, it serves as the precision anchor point for synthesizing stable, temperature-compensated reference voltages from 1.24V to 6.3V.