Texas Instruments BQ27505YZGT-J4

Overview

BQ27505YZGT-J4 from Texas Instruments is a system-side Impedance Track™ fuel gauge IC for single-cell Li-ion battery packs, delivering ±1% state-of-charge (SOC) accuracy, real-time remaining capacity (mAh), time-to-empty (min), and state-of-health (%) via I²C interface. It integrates coulomb counting, internal temperature sensing, and battery insertion detection, and is deployed on host main boards in smartphones and portable media players.

For engineers reviewing the BQ27505YZGT-J4 datasheet, BQ27505YZGT-J4 pinout, BQ27505YZGT-J4 application, or BQ27505YZGT-J4 equivalent, key selection considerations include its 12-ball NanoFree™ CSP package (2.43 mm × 1.96 mm), 400-kHz I²C timing compliance, 4-μA hibernate current, integrated 14-bit ADC for voltage/temperature/sense-resistor monitoring, and support for 5–20 mΩ external sense resistors.

Technical Context

The BQ27505YZGT-J4 implements Texas Instruments' patented Impedance Track™ algorithm to model battery discharge curves, dynamically adjusting for aging, self-discharge, and temperature/rate inefficiencies. It uses dual oscillators - a 2.097-MHz high-frequency oscillator (±4.5% error over –40°C to 85°C) and a 32.768-kHz low-frequency oscillator (±4% error) - to synchronize coulomb integration and temperature sampling.

Its analog front end includes a dedicated integrating ADC for SRP/SRN differential inputs (±0.125 V range, 14–15-bit resolution, 10 μV offset), plus separate 14-bit ADCs for BAT (0–5 V) and TS (thermistor) inputs. Power management supports five modes: NORMAL (114 μA), SLEEP+ (58 μA), SLEEP (19 μA), HIBERNATE (4 μA), and BAT INSERT CHECK.

Key Specifications

Pinout & Package

Package: 12-ball NanoFree™ CSP (YZG), 2.43 mm × 1.96 mm, 0.5 mm pitch, bottom-terminal configuration.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar fuel gauge applications.

Compared with BQ27505YZGT-J4, BQ27426YZFT offers tighter low-temp accuracy but removes battery-insertion detection, while BQ27510-G3YZFT adds integrated switching and broader I/O voltage support at the cost of larger size and higher BOM count.

Availability

BQ27505YZGT-J4 is available at Aetrix Electronics and suitable for smartphone battery management, digital camera power monitoring, handheld terminal energy tracking, and MP3 player battery protection requiring stable component supply across extended production lifecycles.

Supply support for BQ27505YZGT-J4 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 is a global semiconductor leader specializing in analog, embedded processing, and power management technologies, with decades of battery fuel gauge innovation.

The BQ27505YZGT-J4 belongs to TI's Impedance Track™ fuel gauge product line, designed specifically for high-accuracy, system-side battery monitoring in space-constrained portable electronics where removable or embedded Li-ion packs demand long-term SOC fidelity.

FAQ

What is the primary function of the BQ27505YZGT-J4 in a battery management system?

The BQ27505YZGT-J4 serves as a system-side fuel gauge IC that accurately reports remaining capacity (mAh), state-of-charge (%), time-to-empty (min), and state-of-health (%) for single-cell Li-ion batteries. It executes Texas Instruments' Impedance Track™ algorithm using voltage, current, and temperature measurements - all processed internally without host MCU intervention beyond I²C commands. The BQ27505YZGT-J4 resides on the host main board, not inside the battery pack.

Does the BQ27505YZGT-J4 require an external sense resistor, and what value range is supported?

Yes, the BQ27505YZGT-J4 requires an external current-sense resistor connected between PACK– and system ground. It supports resistor values from 5 mΩ to 20 mΩ, enabling precise coulomb counting with minimal voltage drop and power loss. The device's integrating ADC on SRP/SRN pins features ±0.125 V input range and <10 μV offset, ensuring sub-1-mAh resolution even at low currents. The BQ27505YZGT-J4 does not integrate a sense resistor.

How does the BQ27505YZGT-J4 handle battery temperature measurement?

The BQ27505YZGT-J4 supports both internal and external temperature sensing. Its internal sensor covers –40°C to +100°C and is used for basic thermal monitoring. For higher accuracy, it accepts an external 10.0 kΩ NTC thermistor (e.g., Semitec 103AT) on the TS pin, with a recommended 18.2 kΩ pull-up between BI/TOUT and TS. The BQ27505YZGT-J4 uses temperature data to correct OCV lookup tables and adapt Impedance Track™ modeling - critical for maintaining <1% SOC error across operating conditions.

What power-saving modes does the BQ27505YZGT-J4 support, and how low is its minimum current draw?

The BQ27505YZGT-J4 supports five power modes: NORMAL (114 μA), SLEEP+ (58 μA), SLEEP (19 μA), HIBERNATE (4 μA), and BAT INSERT CHECK. HIBERNATE mode delivers the lowest active current draw at 4 μA - ideal for long-term storage or system suspend states. Mode transitions occur automatically based on I²C activity, SOC thresholds, or host-triggered commands like SET_HIBERNATE. The BQ27505YZGT-J4 maintains flash data integrity and retains calibration in all modes.

Can the BQ27505YZGT-J4 be used with removable battery packs, and what connections are required?

Yes, the BQ27505YZGT-J4 is explicitly designed for both embedded and removable single-cell Li-ion battery packs. Only three physical connections are required to the pack: PACK+ (to BAT pin), PACK– (to SRP), and thermistor (to TS). The BI/TOUT pin enables battery insertion detection and thermistor multiplexing. No communication lines (I²C) or power (VCC) run to the pack - all intelligence remains on the host board, simplifying pack design and certification. The BQ27505YZGT-J4 manages all gauging functions autonomously once configured.