Analog Devices Inc. LTC1731EMS8-4.2#PBF

Overview

LTC1731EMS8-4.2#PBF from Analog Devices (formerly Linear Technology) is a single-cell lithium-ion linear battery charger controller in an 8-pin MSOP package, delivering ±1% float voltage accuracy at 4.2 V, programmable charge current up to 500 mA via external R_PROG/R_SENSE, and C/10 end-of-charge detection for portable power management in space-constrained applications.

For engineers reviewing the LTC1731EMS8-4.2#PBF datasheet, LTC1731EMS8-4.2#PBF pinout, LTC1731EMS8-4.2#PBF application, or LTC1731EMS8-4.2#PBF equivalent, key selection considerations include its 4.2 V fixed float voltage, 7 µA sleep-mode battery drain, programmable timer termination, automatic trickle-charge initiation below 2.457 V, and compatibility with external P-channel MOSFET or high-gain PNP pass devices.

Technical Context

The LTC1731EMS8-4.2#PBF implements a dual-loop linear control architecture: a current amplifier servoing the DRV pin to regulate IBAT via R_SENSE, and a voltage amplifier comparing BAT against an internal 2.457 V reference scaled by a precision resistor divider to enforce 4.2 V float regulation. It integrates undervoltage lockout (4.1 V threshold), automatic sleep mode when V_CC − V_BAT ≤ 54 mV, and a 320 ms debounced C/10 comparator.

Its TIMER pin accepts an external capacitor (e.g., 0.1 µF) to set total charge time per t_TIMER = (C_TIMER × 3 hours)/0.1 µF, while floating the PROG pin forces shutdown (I_CC = 1 mA), and shorting TIMER to GND disables only the timer and C/10 functions-enabling constant-current-only operation for NiMH/NiCd charging.

Key Specifications

Pinout & Package

Package: 8-lead plastic MSOP (3 mm × 3 mm, 0.65 mm pitch), moisture sensitivity level 1, RoHS-compliant, with exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1731EMS8-4.2#PBF, LTC4053-4.2 trades external component flexibility for integration and footprint reduction, while MAX1555 sacrifices input voltage range and programmability for USB-native simplicity - making LTC1731EMS8-4.2#PBF optimal for multi-source, multi-chemistry, and precision-regulation requirements.

Availability

LTC1731EMS8-4.2#PBF is available at Aetrix Electronics and suitable for cellular phones, handheld computers, charging docks and cradles, and programmable current source applications requiring stable component supply, long-term lifecycle support, and guaranteed traceable sourcing.

Supply support for LTC1731EMS8-4.2#PBF 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, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.

The LTC1731EMS8-4.2#PBF belongs to Linear's legacy battery management product line, engineered specifically for autonomous, low-component-count linear charging of single-cell Li-ion batteries in portable electronics where precision, reliability, and minimal external parts are critical.

FAQ

What is the exact float voltage setpoint for LTC1731EMS8-4.2#PBF?

The LTC1731EMS8-4.2#PBF has a factory-trimmed internal resistor divider that fixes the regulated battery float voltage at 4.2 V with ±1% accuracy (4.158 V to 4.242 V) over the full –40°C to +85°C operating temperature range and 5 V to 12 V input supply. This value is immutable and distinct from the LTC1731EMS8-4.1#PBF variant (4.1 V).

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

The LTC1731EMS8-4.2#PBF automatically initiates trickle charging when the BAT pin voltage falls below 2.457 V, delivering 10% of the programmed full-scale current until the cell recovers above this threshold. If the low voltage persists for one quarter of the total timer duration, the IC terminates charging and forces the CHRG pin into high-impedance state to indicate a defective cell.

Can LTC1731EMS8-4.2#PBF be used to charge NiMH batteries?

Yes - LTC1731EMS8-4.2#PBF supports NiMH charging in constant-current-only mode by connecting the TIMER pin directly to VCC, which disables the voltage regulation loop, timer, and trickle charge functions. External termination (e.g., –ΔV or temperature cutoff) must then be implemented, as the IC no longer provides C/10 or voltage-based termination.

What is the minimum recommended bypass capacitance for the VCC pin of LTC1731EMS8-4.2#PBF?

The LTC1731EMS8-4.2#PBF requires a minimum 1 µF ceramic capacitor placed as close as possible to the VCC pin and GND to ensure stable operation and suppress input ripple. This value is specified in the datasheet's "Typical Application" schematics and is critical for preventing oscillation during transient load changes.

Does LTC1731EMS8-4.2#PBF require an external sense resistor, and what tolerance is recommended?

Yes - LTC1731EMS8-4.2#PBF requires an external sense resistor (R_SENSE) between VCC and SENSE pins to set charge current. For best accuracy and stability over temperature, 1% tolerance metal-film or thin-film resistors are recommended, as stated in the "Programming Charge Current" section of the datasheet; typical values range from 0.082 Ω to 0.2 Ω depending on desired I_BAT.