Analog Devices Inc. LTC1731EMS8-4.2#TRPBF

Overview

LTC1731EMS8-4.2#TRPBF from Analog Devices (formerly Linear Technology) is a single-cell lithium-ion linear battery charger controller in an 8-pin MSOP package. It delivers ±1% float voltage accuracy at 4.2V, supports programmable charge current up to 500mA via external R_PROG/R_SENSE, and features C/10 end-of-charge detection, automatic trickle charge for low-voltage cells (<2.457V), and sleep mode with 7µA battery drain. It is used in compact portable electronics requiring precise, low-noise charging without switching noise.

For engineers reviewing the LTC1731EMS8-4.2#TRPBF datasheet, LTC1731EMS8-4.2#TRPBF pinout, LTC1731EMS8-4.2#TRPBF application, or LTC1731EMS8-4.2#TRPBF equivalent, key selection criteria include float voltage tolerance (±1%), programmable current accuracy (5%), sleep-mode battery leakage (7µA typ), C/10 detection reliability, and compatibility with P-channel MOSFET or high-gain PNP pass devices.

Technical Context

The LTC1731EMS8-4.2#TRPBF implements a two-stage linear charging architecture: constant-current (CC) followed by constant-voltage (CV) regulation. Its internal 2.457V reference and precision resistor divider set the 4.2V float voltage with ±1% max error over temperature and line. Charge current is determined by the ratio of R_PROG and R_SENSE per IBAT = (2.457V × 800Ω)/(R_PROG × R_SENSE), enabling accurate scaling across 70–585mA.

Termination logic combines analog C/10 current sensing and a capacitor-programmable timer (t_TIMER = CTIMER × 3h / 0.1µF). The CHRG pin provides three-state status output (active-low during CC, weak-pull-down at C/10, high-Z after timeout or sleep), while automatic shutdown occurs when PROG is floated or V_CC drops below UVLO (4.1V) or falls within 54mV of V_BAT.

Key Specifications

Pinout & Package

Package: 8-pin MSOP (3mm × 3mm, 0.65mm pitch), moisture-sensitive level 1, RoHS-compliant, tape-and-reel (TRPBF).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar linear battery charger controller applications.

Compared with MAX1555 and BQ24075, the LTC1731EMS8-4.2#TRPBF offers superior voltage accuracy (±1% vs ±1.5%), external current programmability, and autonomous trickle charge-making it optimal for precision, low-noise, and deeply discharged cell recovery applications where discrete pass device control is preferred.

Availability

LTC1731EMS8-4.2#TRPBF is available at Aetrix Electronics and suitable for smartphone charging circuits, handheld medical devices, USB-C docking stations, and industrial handheld scanners requiring stable component supply, long-lifecycle support, and consistent parametric performance across production batches.

Supply support for LTC1731EMS8-4.2#TRPBF 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

Analog Devices acquired Linear Technology in 2017 and maintains its high-precision analog IC portfolio. Linear pioneered high-performance power management ICs with emphasis on accuracy, low noise, and robustness in demanding applications.

The LTC1731EMS8-4.2#TRPBF belongs to Linear's legacy battery management product line, designed specifically for compact, noise-sensitive, single-cell Li-ion charging where simplicity, accuracy, and ultra-low quiescent current are critical.

FAQ

What is the exact float voltage setting for LTC1731EMS8-4.2#TRPBF?

The LTC1731EMS8-4.2#TRPBF is factory-trimmed to deliver a nominal 4.2V float voltage with a maximum tolerance of ±1% (4.158V to 4.242V) across the full –40°C to +85°C operating range and 5V ≤ V_CC ≤ 12V. This value is fixed and cannot be adjusted externally - the "-4.2" suffix explicitly denotes this variant. The internal resistor divider and 2.457V reference ensure this accuracy without calibration.

How does LTC1731EMS8-4.2#TRPBF handle deeply discharged batteries?

The LTC1731EMS8-4.2#TRPBF automatically initiates trickle charge when the BAT pin voltage is below 2.457V (typical), delivering ~10% of the programmed full-scale current until the cell reaches that threshold. This prevents damage from high-current charging of over-discharged cells. If the voltage remains below 2.35V for one quarter of the total timer duration, the IC terminates charging and forces CHRG into high-Z state as a defective battery indicator.

Can LTC1731EMS8-4.2#TRPBF be used with NiMH batteries?

Yes - LTC1731EMS8-4.2#TRPBF supports NiMH charging in constant-current-only mode by connecting the TIMER pin to V_CC. This disables the CV regulation, timer, and trickle charge functions, turning the IC into a programmable current source. External termination (e.g., –ΔV, temperature cutoff, or timer) must be implemented, as the IC no longer regulates voltage or auto-terminates based on C/10.

What is the minimum recommended R_SENSE value for LTC1731EMS8-4.2#TRPBF?

The minimum recommended R_SENSE is 0.1Ω, corresponding to a 100mV sense voltage at 1A. However, for the LTC1731EMS8-4.2#TRPBF's typical 500mA application, 0.2Ω is standard (yielding 100mV drop). Lower values increase sensitivity to PCB trace resistance and noise; values below 0.1Ω risk violating the 100mV minimum sense voltage requirement for stable current regulation and may degrade accuracy due to amplifier offset effects.

Does LTC1731EMS8-4.2#TRPBF require external compensation components?

No - LTC1731EMS8-4.2#TRPBF is internally compensated and stable with a P-channel MOSFET pass device without external compensation. A 10µF capacitor at the BAT pin is recommended for ripple suppression when the battery is disconnected. If using a PNP transistor instead, a 1000pF capacitor from DRV to V_CC is required for loop stability, per the datasheet design guidelines.