Texas Instruments LM3420M5-8.2/NOPB

Overview

LM3420M5-8.2/NOPB from Texas Instruments (formerly National Semiconductor) is a precision shunt-mode lithium-ion battery charge controller IC designed for end-of-charge voltage regulation in 2-cell (8.2 V nominal) battery packs. It integrates a bandgap reference, compensated op amp, open-emitter NPN output transistor, and internal feedback resistors. With ±0.5% initial regulation tolerance (A-grade), 85 µA quiescent current, and 15 mA output drive capability, it enables accurate constant-voltage termination in linear or switching charger topologies for portable medical devices and power tools.

For engineers reviewing the LM3420M5-8.2/NOPB datasheet, LM3420M5-8.2/NOPB pinout, LM3420M5-8.2/NOPB application, or LM3420M5-8.2/NOPB equivalent, key selection criteria include its fixed 8.2 V regulation voltage, SOT23-5 package footprint, open-emitter output architecture requiring external pass device control, temperature-stable bandgap reference, and compatibility with CC/CV charging loop compensation via the COMP pin.

Technical Context

The LM3420M5-8.2/NOPB implements a precision shunt-regulator topology where the IN pin senses battery voltage and the OUT pin sources current to control an external pass element (e.g., MOSFET or BJT). Its internal 8.2 V bandgap reference achieves ±0.5% tolerance over −40°C to +85°C ambient, with curvature-corrected drift compensation. The error amplifier's inverting input is exposed at the COMP pin to support external frequency compensation using a single capacitor.

It operates as a closed-loop feedback driver: when battery voltage approaches 8.2 V, the output transistor begins sourcing current into the base/gate of the external power stage, transitioning the charger from constant-current to constant-voltage mode. The internal 176 kΩ feedback resistor (Rf) sets gain and phase margin, with min/max values specified across temperature for stability analysis.

Key Specifications

Pinout & Package

The LM3420M5-8.2/NOPB is housed in a 5-lead SOT23-5 package (NS package code MF05A), with pin 1 marked by a dot. Thermal performance is optimized by soldering pin 5 (NC) to PCB copper for heat transfer.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar lithium-ion battery charge controller applications.

Compared with TPS650230RSLR and MAX1555, the LM3420M5-8.2/NOPB offers unique value in discrete, analog-controlled CC/CV loops-enabling design flexibility, lower BOM cost, and deterministic timing behavior without firmware dependencies, making it ideal for safety-critical or resource-constrained embedded systems.

Availability

LM3420M5-8.2/NOPB is available at Aetrix Electronics and suitable for portable power tools, medical infusion pumps, industrial handheld scanners, and wearable health monitors requiring stable component supply and long-term manufacturability.

Supply support for LM3420M5-8.2/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 acquired National Semiconductor in 2011 and maintains full product continuity, documentation, and technical support for legacy analog ICs like the LM3420 series.

The LM3420 product line was engineered specifically for precision, low-power shunt-based Li-ion charge control-targeting applications where discrete topology, analog stability, and minimal quiescent current are prioritized over digital integration.

FAQ

What is the exact regulation voltage of the LM3420M5-8.2/NOPB?

The LM3420M5-8.2/NOPB has a nominal regulation voltage of 8.2 V, with a guaranteed tolerance of ±0.5% for the A-grade version (LM3420AM5-8.2) and ±1% for the standard grade. The LM3420M5-8.2/NOPB is the standard-grade variant, so its regulation voltage falls within 8.118 V to 8.282 V at 25°C and across the full −40°C to +85°C operating range.

Can the LM3420M5-8.2/NOPB be used for 3-cell or 4-cell Li-ion batteries?

No-the LM3420M5-8.2/NOPB is factory-trimmed exclusively for 8.2 V regulation, corresponding to two 4.1 V Li-ion cells. For 3-cell (12.6 V) or 4-cell (16.8 V) applications, TI specifies dedicated variants: LM3420M5-12.6 and LM3420M5-16.8. Using LM3420M5-8.2/NOPB in higher-voltage configurations would result in premature charge termination and undercharged batteries.

Does the LM3420M5-8.2/NOPB require external compensation components?

Yes-the COMP pin of the LM3420M5-8.2/NOPB must be externally compensated for stable CC/CV loop operation. A single capacitor from COMP to OUT is typically sufficient; recommended values range from 100 pF to 1 nF depending on external pass device characteristics and desired transient response. The LM3420M5-8.2/NOPB datasheet provides Bode plots and response-time curves to guide selection.

What is the function of pin 5 (NC) on the LM3420M5-8.2/NOPB?

Pin 5 on the LM3420M5-8.2/NOPB has no internal electrical connection but is thermally bonded to the die substrate. It must be soldered to a PCB copper pour to enhance heat dissipation and ensure reliable operation at elevated ambient temperatures. Leaving pin 5 floating degrades thermal performance and may cause premature thermal shutdown or parameter drift.

How does the LM3420M5-8.2/NOPB interface with an external MOSFET in a linear charger?

The LM3420M5-8.2/NOPB drives the gate of an external N-channel MOSFET via its open-emitter OUT pin. A pull-up resistor from OUT to a bias rail (e.g., input voltage) establishes the off-state; as battery voltage nears 8.2 V, the LM3420M5-8.2/NOPB sinks current through OUT, pulling the MOSFET gate low to reduce conduction and enforce constant voltage. This configuration requires careful attention to gate drive strength and Miller capacitance to avoid oscillation.