Texas Instruments BQ27505YZGR-J2

Overview

BQ27505YZGR-J2 from Texas Instruments is a system-side Impedance Track™ fuel gauge IC for single-cell Li-ion battery packs, providing real-time state-of-charge (%), remaining capacity (mAh), time-to-empty (min), voltage (mV), temperature (°C), and state-of-health (%) with <1% SOC error. It resides on the host system main board-not inside the battery-and interfaces via 400-kHz I²C to microcontrollers in space-constrained portable electronics.

For engineers reviewing the BQ27505YZGR-J2 datasheet, BQ27505YZGR-J2 pinout, BQ27505YZGR-J2 application, or BQ27505YZGR-J2 equivalent, key selection considerations include its 12-ball NanoFree™ CSP package, ultra-low quiescent current (4 µA in Hibernate mode), integrated coulomb counter with 14–15-bit resolution, internal temperature sensor, and support for external NTC thermistor (10.0 kΩ, B25/85 = 3435 K) with dedicated TS and BI/TOUT pins.

Technical Context

The BQ27505YZGR-J2 implements Texas Instruments' patented Impedance Track™ algorithm to model battery discharge curves and dynamically adjust for aging, self-discharge, and temperature/rate inefficiencies-enabling accurate time-to-empty predictions without battery-side firmware. It uses dual oscillators (2.097 MHz HF and 32.768 kHz LF) and an integrating ADC for coulomb counting with ±0.034% FSR INL and 10 µV input offset.

Power management includes five operational modes-NORMAL (114 µA), SLEEP+ (58 µA), SLEEP (19 µA), HIBERNATE (4 µA), and BAT INSERT CHECK-with automatic transitions triggered by events like battery insertion or low-load conditions. Communication occurs over a standard 400-kHz I²C interface with open-drain SDA/SCL, configurable interrupt outputs (BAT_LOW, SOC_INT), and push-pull status indicators (BAT_GD).

Key Specifications

Pinout & Package

Package: 12-ball NanoFree™ CSP (2.43 mm × 1.96 mm, 0.5 mm pitch), optimized for ultra-thin mobile PCBs with minimal footprint and thermal resistance (θ_JA = 89°C/W).

Key Features

Applications

Equivalent & Alternatives

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

Compared with BQ27505YZGR-J2, the BQ27426YZFT trades thermal sensing fidelity and I²C bandwidth for footprint reduction, while the BQ27510G3YZFT adds multi-cell scalability and EEPROM longevity at the cost of increased software integration effort.

Availability

BQ27505YZGR-J2 is available at Aetrix Electronics and suitable for smartphones, digital still cameras, handheld terminals, and MP3/multimedia players requiring stable component supply, long-term lifecycle support, and validated fuel gauging performance in space-constrained designs.

Supply support for BQ27505YZGR-J2 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 management IP development.

The BQ27505YZGR-J2 belongs to TI's Impedance Track™ fuel gauge product line, engineered specifically for system-side battery monitoring in portable consumer electronics where accuracy, ultra-low power, and minimal PCB footprint are critical design constraints.

FAQ

What is the primary function of the BQ27505YZGR-J2 in a portable electronics design?

The BQ27505YZGR-J2 serves as a system-side fuel gauge IC that accurately reports remaining capacity (mAh), state-of-charge (%), time-to-empty (min), voltage (mV), temperature (°C), and state-of-health (%) for single-cell Li-ion batteries. Unlike pack-integrated gauges, it resides on the host main board and communicates via I²C-eliminating the need for battery-side firmware while maintaining <1% SOC error across aging and temperature variations. Its role is to provide the host microcontroller with reliable, real-time battery metrics for UI display, power management, and safety decisions.

Does the BQ27505YZGR-J2 require an external sense resistor, and what value range is supported?

Yes, the BQ27505YZGR-J2 requires an external low-value sense resistor connected between PACK– and system ground to measure charge/discharge current. The datasheet specifies support for 5 mΩ to 20 mΩ resistors, with typical use at 10 mΩ. This range balances measurement sensitivity (enabling sub-mA current resolution with the 10 µV input offset) against power dissipation (<20 mW at 2 A). The SRP and SRN pins are dedicated analog inputs for this differential sensing, and the device's integrating ADC provides 14–15-bit resolution for high-accuracy coulomb counting.

How does the BQ27505YZGR-J2 handle temperature measurement-does it rely solely on an external thermistor?

The BQ27505YZGR-J2 supports both internal and external temperature sensing. It includes an integrated temperature sensor for basic ambient monitoring (–40°C to 85°C), but for high-accuracy battery thermal profiling, it is designed to interface with an external NTC thermistor-specifically a 10.0 kΩ ±1% unit with B25/85 = 3435 K ±1%, such as the Semitec 103AT. The TS pin reads the thermistor voltage, while BI/TOUT provides bias and multiplexing control. Using the external path enables precise compensation of SOC and aging models, which is essential for <1% gauging accuracy across operating conditions.

What power-saving modes does the BQ27505YZGR-J2 offer, and how low is its minimum current draw?

The BQ27505YZGR-J2 features five adaptive 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-achieved when the battery is disconnected and the device enters deep storage state. Mode transitions occur automatically based on events like battery insertion or load current thresholds, though the host can also force entry via I²C commands (e.g., SET_HIBERNATE). This ultra-low quiescent current extends system standby time significantly, especially in devices with infrequent usage patterns.

Can the BQ27505YZGR-J2 be used with removable battery packs, or is it limited to embedded configurations?

Yes, the BQ27505YZGR-J2 is explicitly designed to work with both embedded (non-removable) and removable battery packs. Its system-side placement on the main board-rather than inside the battery-allows it to interface directly with PACK+, PACK–, and T terminals regardless of pack form factor. The BI/TOUT pin enables battery-insertion detection, and the device generates a BAT_DET flag upon connection. This architecture eliminates the need for battery-side electronics, simplifies certification, and supports hot-swap scenarios common in professional handhelds and medical devices-all while maintaining the same <1% SOC accuracy specification.