Texas Instruments LM3420M5-4.2

Overview

LM3420M5-4.2 from Texas Instruments (formerly National Semiconductor) is a precision shunt-mode lithium-ion battery charge controller IC designed for single-cell 4.2 V end-of-charge voltage regulation. It integrates a bandgap reference, error amplifier, open-emitter NPN output transistor, and internal feedback resistor (75 kΩ), delivering ±1% regulation tolerance, 85 µA quiescent current, and 15 mA output drive capability in a SOT-23-5 package. It serves as the voltage-sensing and control element in linear or switching Li-ion charger feedback loops.

For engineers reviewing the LM3420M5-4.2 datasheet, LM3420M5-4.2 pinout, LM3420M5-4.2 application, or LM3420M5-4.2 equivalent, key selection criteria include its fixed 4.2 V regulation voltage, SOT-23-5 thermal performance (θ_JA ≈ 306 °C/W), open-emitter output architecture for external power stage control, and compatibility with CC/CV charging topologies requiring <0.5% to ±1% voltage accuracy over −40 °C to +85 °C.

Technical Context

The LM3420M5-4.2 implements a precision shunt-regulator topology where the IN pin senses battery voltage and the OUT pin sources current into an external pass device (e.g., BJT or MOSFET gate) when IN exceeds the 4.2 V regulation threshold. Its internally compensated op amp features externally accessible COMP pin for loop stability tuning via capacitor-to-OUT connection.

It uses a curvature-corrected bandgap reference with 0.5% (A-grade) or 1% (standard grade) initial tolerance and low temperature drift. The 75 kΩ internal feedback resistor sets gain and phase margin; minimum/maximum values (56 kΩ / 94 kΩ) are specified across temperature to ensure stable closed-loop operation in CC/CV chargers.

Key Specifications

Pinout & Package

The LM3420M5-4.2 is housed in a 5-lead SOT-23-5 surface-mount package (NS package code MF05A), with pin 1 marked by a dot. Pin 5 is NC but must be soldered to PCB for optimal thermal conduction.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TLV431AIDBZR and MAX8814EUT+T, the LM3420M5-4.2 uniquely balances precision fixed-voltage regulation, external power stage control, and minimal external components-making it optimal for discrete or modular charger designs where flexibility, thermal management, and topology independence are prioritized over monolithic integration.

Availability

LM3420M5-4.2 is available at Aetrix Electronics and suitable for smartphone battery management, portable medical device charging, and industrial handheld scanner power systems requiring stable component supply and long-term lifecycle support.

Supply support for LM3420M5-4.2 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 technical and supply chain responsibility for legacy analog products including the LM3420 series.

The LM3420 product line was engineered specifically for precision end-of-charge voltage control in lithium-ion battery chargers, targeting applications demanding high accuracy, low quiescent current, and compatibility with both linear and switching topologies.

FAQ

What is the exact regulation voltage tolerance of LM3420M5-4.2 over temperature?

The LM3420M5-4.2 has a standard-grade regulation voltage tolerance of ±1% over the full operating temperature range (−40 °C to +85 °C), with typical room-temperature deviation of ±0.5%. This is verified per Electrical Characteristics table on page 2 of SNVS116C, where VREG limits are specified as 4.158 V (min) and 4.242 V (max) at TJ = 25 °C, and 4.116 V / 4.284 V across temperature. The trimmed bandgap reference includes curvature correction to minimize drift.

Can LM3420M5-4.2 drive a MOSFET gate directly without additional components?

Yes - the LM3420M5-4.2's open-emitter NPN output can directly drive the gate of a P-channel MOSFET (with pull-up resistor) or N-channel MOSFET (with appropriate level-shifting). Its 15 mA sink capability supports typical gate charge requirements for small-signal MOSFETs used in ≤1 A chargers. However, for high-speed switching or large gate capacitance, an external buffer may be needed to meet rise/fall time targets.

Is pin 5 (NC) on LM3420M5-4.2 electrically connected or purely thermal?

Pin 5 is electrically unconnected (NC) - it has no internal bond wire or silicon connection. However, it is thermally coupled to the die paddle and must be soldered to a PCB copper pour to achieve the specified θ_JA of ≈306 °C/W. Leaving pin 5 floating degrades thermal performance and risks exceeding junction temperature limits under sustained 15 mA output current.

How does the COMP pin function in LM3420M5-4.2, and what capacitor value is recommended?

The COMP pin is the inverting input of the internal error amplifier and is used for loop compensation. A capacitor (C_C) from COMP to OUT sets dominant pole frequency; typical values range from 100 pF to 1 nF depending on external circuitry. For standard 4.2 V applications with moderate load step response, 470 pF is commonly used. Exact value must be validated via load-step testing per Figure 17–28 in SNVS116C.

Does LM3420M5-4.2 support external voltage trimming, and how much adjustment is possible?

Yes - the LM3420M5-4.2 supports external VREG trimming up to ±10% using a single resistor from COMP to IN (increase) or COMP to GND (decrease). Trim formulas are provided in SNVS116C Section "VREG External Voltage Trim"; for LM3420M5-4.2, R_increase = 22×10⁵/%incr and R_decrease = (53×10⁵/%decr) −75×10³. Trimming introduces minor tempco degradation but retains functional stability.