Texas Instruments LM3420AM5-8.4

Overview

LM3420AM5-8.4 from Texas Instruments is a precision 8.4-V shunt-mode lithium-ion battery charge controller IC, serving as the voltage reference and feedback control element in constant-current/constant-voltage (CC/CV) charger topologies. It features ±0.5% regulation tolerance at 25°C, 85 μA typical quiescent current, open-emitter NPN output capable of sourcing up to 15 mA, and internal temperature-drift-corrected bandgap reference. It is used in compact 2-cell Li-ion charging circuits with linear or switching regulators.

For engineers reviewing the LM3420AM5-8.4 datasheet, LM3420AM5-8.4 pinout, LM3420AM5-8.4 application, or LM3420AM5-8.4 equivalent, key selection criteria include end-of-charge voltage accuracy, thermal stability over −40°C to +85°C, compensation pin flexibility for loop stability, SOT-23-5 footprint constraints, and compatibility with external power stages such as PNP transistors or optocouplers.

Technical Context

The LM3420AM5-8.4 implements a monolithic shunt regulator architecture with an internally compensated error amplifier, trimmed bandgap reference, and open-emitter NPN output stage. Its IN-to-GND sensing path directly monitors battery voltage, and regulation initiates when IN exceeds 8.4 V, causing the OUT pin to source current into an external transistor or optocoupler base.

Compensation is externally configurable via a capacitor between COMP and OUT pins, enabling loop stability tuning across linear and switching charger designs. The internal 181-kΩ feedback resistor (Rf) exhibits curvature-corrected temperature drift, ensuring <±1% total regulation error over full operating temperature range.

Key Specifications

Pinout & Package

SOT-23-5 (DBV) package: 2.90 mm × 1.60 mm body size, surface-mount, lead-free compatible, thermal resistance R_θJA = 181.2°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV431ACDBVR and MAX8814EUB+T, the LM3420AM5-8.4 provides optimal balance of precision (±0.5%), minimal external components, and SOT-23-5 footprint for discrete-controlled chargers-making it ideal where cost, size, and proven analog control simplicity are prioritized over full integration.

Availability

LM3420AM5-8.4 is available at Aetrix Electronics and suitable for portable medical devices, industrial handheld terminals, wireless sensor nodes, smart power tools, and battery-backed instrumentation requiring stable component supply and long-term obsolescence support.

Supply support for LM3420AM5-8.4 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 delivering analog, embedded processing, and connectivity solutions with emphasis on reliability, precision, and energy efficiency.

The LM3420 series belongs to TI's battery management analog portfolio, specifically engineered for high-accuracy, low-quiescent-current end-of-charge control in discrete Li-ion charger architectures.

FAQ

What is the primary function of the LM3420AM5-8.4 in a Li-ion charging circuit?

The LM3420AM5-8.4 serves as a precision shunt-mode voltage reference and control element that detects when the battery voltage reaches 8.4 V and commands an external power stage (e.g., PNP transistor or optocoupler) to transition from constant-current to constant-voltage charging mode. Its ±0.5% regulation tolerance ensures accurate end-of-charge termination critical for 2-cell Li-ion safety and longevity. The LM3420AM5-8.4 achieves this using an internal bandgap reference, error amplifier, and open-emitter NPN output stage-all integrated in a SOT-23-5 package.

Can the LM3420AM5-8.4 be used for 1-cell or 3-cell Li-ion configurations?

No-the LM3420AM5-8.4 is factory-trimmed exclusively for 8.4 V output, corresponding to two 4.2-V Li-ion cells in series. While the LM3420 family includes other fixed-voltage variants (e.g., LM3420M5-4.2 for 1-cell), the LM3420AM5-8.4 itself does not support reconfiguration for different cell counts. External resistor networks cannot safely or accurately scale its reference; doing so degrades temperature stability and voids the ±0.5% tolerance guarantee. For 1-cell or 3-cell systems, select the appropriate LM3420xM5-x.x variant.

How does the COMP pin function in the LM3420AM5-8.4?

The COMP pin exposes the inverting input of the internal error amplifier, enabling external frequency compensation to stabilize the feedback loop. A capacitor (typically 0.01 µF) is connected between COMP and OUT to set dominant pole location and ensure phase margin >45° across operating conditions. This configuration allows designers to optimize transient response and avoid oscillation when interfacing with diverse external power stages-including linear regulators, switching controllers, or optocoupled isolated supplies. The LM3420AM5-8.4 datasheet provides test circuits and Bode plot guidance for validation.

What is the maximum allowable input voltage applied to the IN pin of the LM3420AM5-8.4?

The absolute maximum rating for the IN pin voltage is 20 V, as specified in the LM3420AM5-8.4 datasheet. Exceeding this value risks permanent damage, even momentarily. In practice, the IN pin should be biased within the recommended operating range of up to 20 V-but sustained operation near this limit requires careful thermal design due to power dissipation in the internal reference and amplifier. For robustness in variable-input applications (e.g., automotive or adapter-fed chargers), a series current-limiting resistor on the OUT pin and clamping diode on IN are recommended per TI application notes.

Does the LM3420AM5-8.4 require external components to operate as a complete charger controller?

Yes-the LM3420AM5-8.4 is a controller-only IC and requires external components to form a functional charger: an external pass device (e.g., PNP transistor or N-channel MOSFET with level-shifting), current-sense resistor for CC mode, compensation capacitor between COMP and OUT, and optionally a trim resistor for fine-tuning. It does not integrate power switches, current sources, or timers. This discrete-control architecture gives designers full flexibility in topology choice (linear, buck, flyback) while retaining precision voltage regulation. The LM3420AM5-8.4 delivers the core 8.4-V reference and control signal-but relies on external circuitry to execute charging.