Texas Instruments LM809M3-4.38/NOPB

Overview

LM809M3-4.38/NOPB from Texas Instruments is a 3-pin SOT-23 microprocessor supervisory circuit with factory-programmed 4.38 V reset threshold, active-low RESET output, 240 ms typical reset timeout, ±3% threshold accuracy over –40°C to 105°C, and 15 µA typical supply current. It monitors 5 V supply rails in embedded controllers during power-up, brown-out, and power-down events.

For engineers reviewing the LM809M3-4.38/NOPB datasheet, LM809M3-4.38/NOPB pinout, LM809M3-4.38/NOPB application, or LM809M3-4.38/NOPB equivalent, key selection criteria include reset threshold tolerance, guaranteed reset assertion below 1 V VCC, transient immunity up to 20 µs at 100 mV underdrive, and compatibility with bidirectional µP reset pins via 4.7 kΩ series resistor.

Technical Context

The LM809M3-4.38/NOPB implements a precision bandgap-based voltage comparator with internal hysteresis to detect VCC falling below 4.38 V (±3% over temperature), triggering an active-low RESET signal that remains asserted for 240 ms after VCC recovers above threshold. Its design ensures monotonic reset behavior without chatter during slow-rising or noisy supply conditions.

It operates across full industrial temperature range (–40°C to 105°C) with guaranteed functionality down to VCC = 1.0 V, supports transient rejection via internal filtering, and maintains valid RESET output state even as VCC collapses toward ground-enabling reliable system initialization in battery-backed or low-power wake-up scenarios.

Key Specifications

Pinout & Package

SOT-23 (DBZ) package, 2.92 mm × 1.30 mm body size, 3-pin surface-mount outline with Q3 pin-1 quadrant orientation per tape-and-reel specification.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microprocessor reset applications.

Compared with MAX809TRD3-T and TPS3808G33DBVR, LM809M3-4.38/NOPB delivers exact 4.38 V threshold alignment with 5 V supply brown-out margins, fixed 240 ms timing optimized for legacy µP reset specs, and proven interoperability with bidirectional reset pins-making it the preferred choice for retrofitting or maintaining existing industrial control designs.

Availability

LM809M3-4.38/NOPB is available at Aetrix Electronics and suitable for industrial PLC controllers, smart energy meters, factory automation HMIs, and renewable inverter control boards requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LM809M3-4.38/NOPB 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, with decades of experience in high-reliability industrial and automotive ICs.

The LM809 family was designed specifically for cost-sensitive, space-constrained microprocessor supervision in industrial automation and metering applications-emphasizing precision threshold accuracy, low power, and robust transient immunity in minimal 3-pin SOT-23 packaging.

FAQ

What is the exact reset threshold voltage of LM809M3-4.38/NOPB and how does it vary with temperature?

The LM809M3-4.38/NOPB has a factory-programmed reset threshold of 4.38 V with ±3% tolerance over –40°C to 85°C (4.25 V to 4.50 V). At –40°C to 105°C, min/max expands to 4.16 V/4.56 V. Temperature coefficient is 30 ppm/°C, resulting in <±15 mV total drift across full range-ensuring consistent brown-out detection in thermal-cycling environments.

Does LM809M3-4.38/NOPB provide a valid reset signal when VCC drops below 1 V?

Yes. The LM809M3-4.38/NOPB guarantees RESET output validity down to VCC = 1.0 V. Below this, the output enters high-impedance state. To maintain defined logic level during full collapse, TI recommends a 100 kΩ pull-down resistor from RESET to GND-ensuring predictable behavior in battery-dead or catastrophic power-fail scenarios.

Can LM809M3-4.38/NOPB interface directly with microprocessors having bidirectional reset pins?

Yes, but requires a 4.7 kΩ series resistor between LM809M3-4.38/NOPB RESET and the µP reset pin (as shown in Figure 9 of SNVS052E). This isolates the open-drain output from potential contention when the µP drives its reset pin high, preventing latch-up or excessive current while preserving clean reset assertion timing.

What is the recommended bypass capacitor for LM809M3-4.38/NOPB and why is it critical?

A 0.1 µF ceramic capacitor must be placed as close as possible to the VCC pin of LM809M3-4.38/NOPB. This suppresses high-frequency transients on the monitored rail-preventing false resets triggered by switching noise, ESD coupling, or DC-DC ripple. Without it, the device may assert RESET during benign supply fluctuations, compromising system reliability.

How does the 240 ms reset timeout of LM809M3-4.38/NOPB benefit microprocessor initialization?

The 240 ms typical timeout ensures the microprocessor completes all internal power-on sequences-including clock stabilization, PLL lock, memory controller calibration, and watchdog initialization-before RESET deassertion. This eliminates race conditions that cause boot failures, corrupted register states, or undefined peripheral behavior in complex embedded systems.