Analog Devices Inc. LTC1731ES8-4.2#PBF

Overview

LTC1731ES8-4.2#PBF from Analog Devices (formerly Linear Technology) is a single-cell lithium-ion linear battery charger controller with internal 4.2V float voltage regulation, ±1% output accuracy, 500mA programmable charge current (via RPROG/RSENSE), and C/10 end-of-charge detection. It operates from 4.5V to 12V input, supports automatic trickle charge for low-voltage cells (<2.457V), and enters 7µA sleep mode when input is removed - used in handheld computers and charging docks.

For engineers reviewing the LTC1731ES8-4.2#PBF datasheet, LTC1731ES8-4.2#PBF pinout, LTC1731ES8-4.2#PBF application, or LTC1731ES8-4.2#PBF equivalent, key selection criteria include float voltage tolerance (±1%), external MOSFET/PNP drive capability, PROG-pin shutdown behavior, and TIMER-pin programmable termination timing (CTIMER-based).

Technical Context

The LTC1731ES8-4.2#PBF implements a dual-loop linear control architecture: a current amplifier (CA) servoing external P-channel MOSFET gate via DRV pin to regulate IBAT through RSENSE, and a voltage amplifier (VA) reducing charge current as BAT approaches 4.2V. Trickle charge initiates below 2.457V and delivers 10% of full-scale current until cell voltage rises or timer expires.

Charge termination uses two independent mechanisms: C/10 current detection (with 320ms latch delay) and a programmable timer set by CTIMER (tTIMER = 3h × CTIMER/0.1µF). The CHRG pin provides open-drain status signaling - pulled low during fast charge, weakly pulled to GND at C/10, and high-impedance after timer expiry or shutdown.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (Small Outline, narrow 0.150") - RoHS-compliant, surface-mount, footprint compatible with industry-standard SOIC-8 layouts.

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 and LTC1732ES8-4.2, the LTC1731ES8-4.2#PBF offers minimal-feature, low-cost linear charging with proven reliability in fixed-input docked applications - ideal where deterministic timing, compact external component count, and strict 4.2V regulation are primary requirements.

Availability

LTC1731ES8-4.2#PBF is available at Aetrix Electronics and suitable for handheld computers, charging docks, and legacy cellular phones requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for LTC1731ES8-4.2#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 acquired Linear Technology in 2017 and maintains full product support, documentation, and manufacturing continuity for legacy Linear parts including the LTC1731 series.

The LTC1731 belongs to Linear's precision battery management IC family, designed specifically for cost-sensitive, firmware-free linear charging of single-cell Li-ion batteries in portable consumer electronics.

FAQ

What is the exact float voltage setpoint of the LTC1731ES8-4.2#PBF?

The LTC1731ES8-4.2#PBF has a factory-trimmed internal float voltage of 4.2V with guaranteed accuracy of ±1% (4.158V to 4.242V) over the full –40°C to 85°C operating temperature range. This value is fixed and cannot be adjusted externally - it is distinct from the LTC1731ES8-4.1#PBF variant, which is trimmed to 4.1V.

Can the LTC1731ES8-4.2#PBF be used to charge NiMH batteries?

Yes, the LTC1731ES8-4.2#PBF can charge NiMH batteries in constant-current-only mode by connecting the TIMER pin to VCC, which disables the voltage regulation loop and timer. However, external termination (e.g., ΔV or temperature cutoff) must be implemented, as the LTC1731ES8-4.2#PBF does not provide NiMH-specific termination algorithms.

What happens to the CHRG pin during different charge states of the LTC1731ES8-4.2#PBF?

During fast charge, the CHRG pin is actively pulled low by an internal N-channel MOSFET. At C/10 (10% of programmed current), the MOSFET turns off and a 100µA current source pulls CHRG toward GND. After timer expiry or shutdown, CHRG enters high-impedance state - enabling three-state detection (low, weak-low, open) for µC or LED interfacing.

How is charge current programmed on the LTC1731ES8-4.2#PBF?

Charge current is set by two external resistors: RPROG from PROG pin to GND, and RSENSE between VCC and SENSE pin. The formula is IBAT = (2.457V × 800Ω) / (RPROG × RSENSE). For 500mA, typical values are RPROG = 19.6kΩ and RSENSE = 0.2Ω - both should be 1% tolerance for best accuracy.

Does the LTC1731ES8-4.2#PBF require external compensation components?

No, the LTC1731ES8-4.2#PBF is internally compensated and stable with a P-channel MOSFET pass device without additional capacitors. However, a 10µF capacitor is recommended at the BAT pin when the battery is disconnected to maintain loop stability, and a 1000pF capacitor from DRV to VCC is required if using a PNP transistor instead of a MOSFET.