Analog Devices Inc. LTC1731ES8-8.2#PBF

Overview

LTC1731ES8-8.2#PBF from Analog Devices (formerly Linear Technology) is a complete constant-current/constant-voltage linear charger controller for 2-cell lithium-ion batteries, delivering 8.2V regulated float voltage with ±1% accuracy, programmable charge current up to 500mA via external R_PROG/R_SENSE, and automatic trickle charge initiation below 4.95V - used in handheld computing and charging cradles requiring precise dual-cell Li-Ion management.

For engineers reviewing the LTC1731ES8-8.2#PBF datasheet, LTC1731ES8-8.2#PBF pinout, LTC1731ES8-8.2#PBF application, or LTC1731ES8-8.2#PBF equivalent, key selection criteria include its 8.2V fixed float voltage, C/10 end-of-charge detection, programmable timer termination, sleep-mode battery drain of 15µA, and SO-8 package compatibility with space-constrained portable power systems.

Technical Context

The LTC1731ES8-8.2#PBF implements a precision analog control loop using an internal 2.457V reference, trimmed 800Ω resistor, and current amplifier to servo an external P-channel MOSFET or high-gain PNP pass device. It integrates undervoltage lockout (8.2V V_UVLO), automatic trickle charge (10% I_BAT below 4.95V), and C/10 comparator latching after 320ms delay to prevent transient false triggers.

Charge termination is dual-mode: time-based via external capacitor on TIMER pin (3 hours/µF), or voltage-based via internal resistor divider setting 8.2V float; disabling the timer by pulling TIMER to V_CC enables constant-current-only operation suitable for NiMH/NiCd charging with external termination.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (Small Outline, narrow 0.150-inch body), RoHS-compliant, surface-mount.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1731ES8-8.4#PBF, the LTC1731ES8-8.2#PBF provides lower float voltage for 4.1V/cell chemistries, while LTC4050ES8#PBF trades timer/C/10 capability for integrated thermal management - making LTC1731ES8-8.2#PBF optimal for cost-sensitive, non-thermal-critical 2-cell Li-Ion systems needing precise termination control.

Availability

LTC1731ES8-8.2#PBF is available at Aetrix Electronics and suitable for handheld computers, charging docks and cradles, and legacy cellular phones requiring stable component supply, long-lifecycle support, and RoHS-compliant SO-8 packaging.

Supply support for LTC1731ES8-8.2#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 its portfolio of high-performance analog ICs, including precision power management solutions for demanding portable applications.

The LTC1731 product line was designed specifically for compact, efficient linear charging of multi-cell lithium-ion batteries in space-constrained portable equipment where simplicity, accuracy, and low quiescent current are critical.

FAQ

What is the exact float voltage setpoint of the LTC1731ES8-8.2#PBF?

The LTC1731ES8-8.2#PBF has a factory-trimmed internal resistor divider that sets a precise 8.2V regulated float voltage at the BAT pin, with guaranteed accuracy of ±1% (8.118V to 8.282V) across the full –40°C to +85°C operating temperature range and 9V–12V V_CC supply.

Can the LTC1731ES8-8.2#PBF be used to charge NiMH or NiCd batteries?

Yes, the LTC1731ES8-8.2#PBF can charge NiMH or NiCd batteries in constant-current-only mode by connecting the TIMER pin to V_CC, which disables the voltage regulation loop and timer. External termination (e.g., –ΔV or temperature cutoff) remains required, as the LTC1731ES8-8.2#PBF does not provide built-in NiMH/NiCd termination logic.

How does the LTC1731ES8-8.2#PBF enter and exit sleep mode?

The LTC1731ES8-8.2#PBF automatically enters sleep mode when V_CC drops below V_BAT + 54mV (e.g., input supply removal), reducing battery drain current to 15µA typical. It exits sleep mode when V_CC rises above the 8.2V UVLO threshold and a valid R_PROG is connected to ground - no reset or external signal is needed.

What is the function of the PROG pin on the LTC1731ES8-8.2#PBF besides programming charge current?

In addition to setting charge current via R_PROG, the PROG pin serves as a shutdown input: floating the pin allows the internal 2.5µA current source to pull it above 2.457V, forcing the LTC1731ES8-8.2#PBF into shutdown mode with I_CC ≈ 1mA and DRV pulled to V_CC to disable the external pass device.

Does the LTC1731ES8-8.2#PBF require external compensation components for stability?

No external compensation is required when using a P-channel MOSFET as the pass device. However, a minimum 10µF capacitor is required at the BAT pin for loop stability when the battery is disconnected, and a 1nF capacitor from DRV to V_CC is mandatory when using a PNP transistor to ensure voltage-loop stability - both specified in the LTC1731ES8-8.2#PBF datasheet.