Texas Instruments BQ29405DCT3

Overview

BQ29405DCT3 from Texas Instruments is a BiCMOS secondary overvoltage protection IC for 2-, 3-, or 4-cell Li-ion battery packs, featuring 4.65 V ±25 mV precision cell voltage detection, programmable delay via external capacitor on CD pin, <2 µA supply current, and high-accuracy hysteresis (300 mV). It activates an external N-channel FET to blow a fuse in the positive battery rail during overvoltage events, used in notebook PC battery packs requiring redundant safety protection.

For engineers reviewing the BQ29405DCT3 datasheet, BQ29405DCT3 pinout, BQ29405DCT3 application, or BQ29405DCT3 equivalent, key selection criteria include second-level protection threshold accuracy, CD-pin-based delay configurability, ultra-low quiescent current, and compatibility with 2–4 series cell topologies in portable medical and instrumentation systems.

Technical Context

The BQ29405DCT3 implements a precision voltage comparator bank monitoring VC1–VC2, VC2–VC3, VC3–VC4, and VC4–GND differential voltages against a fixed 4.65 V reference. When any cell exceeds this threshold, a 0.2 µA internal current source charges the external CD capacitor until V_CD reaches 1.2 V, triggering OUT high.

After activation, OUT remains high until all cell voltages fall below (4.65 V – 300 mV) hysteresis level. The device operates across –25°C to 85°C, supports up to 28 V input on all sense pins, and maintains stable operation during pulse charging due to high ripple rejection.

Key Specifications

Pinout & Package

Package: SSOP-8 (DCT), 3.0 mm × 3.0 mm × 1.3 mm body, 0.65 mm pitch, RoHS-compliant SNBI lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar secondary Li-ion overvoltage protection applications.

Compared with BQ29405DCT3, BQ29401DCT3 offers earlier overvoltage intervention for conservative chemistries, while BD14000GUL reduces cost and complexity at the expense of 4-cell topology support and pin-level compatibility - making BQ29405DCT3 the sole option for high-accuracy, fully independent 4S secondary protection.

Availability

BQ29405DCT3 is available at Aetrix Electronics and suitable for notebook PC battery packs, portable medical devices, test equipment, and industrial handheld scanners requiring stable component supply and long-lifecycle support.

Supply support for BQ29405DCT3 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and personal electronics markets.

The BQ2940x family was designed specifically for secondary overvoltage protection in multi-cell Li-ion battery packs, addressing the need for autonomous, low-power, high-accuracy hardware-level safety beyond primary protection ICs.

FAQ

What is the exact overvoltage detection threshold of the BQ29405DCT3?

The BQ29405DCT3 has a factory-trimmed overvoltage detection threshold of 4.65 V ±25 mV across –25°C to 85°C. This value is specified in the Electrical Characteristics table of the SLUS568C datasheet and applies to all four differential cell voltage inputs (VC1–VC2, VC2–VC3, VC3–VC4, VC4–GND). The BQ29405DCT3 is the only variant in the bq2940x family with this specific 4.65 V setting.

How does the BQ29405DCT3 implement programmable delay time?

The BQ29405DCT3 uses an internal 0.2 µA current source to charge an external capacitor connected to the CD pin. Delay time is calculated as t_D = (1.2 V × C_DELAY) / 0.2 µA. For example, a 0.22 µF capacitor yields ~1.32 s typical delay. The BQ29405DCT3 resets this timer if all cell voltages drop below (4.65 V – 300 mV) before CD reaches 1.2 V.

Can the BQ29405DCT3 be used in a 2-cell Li-ion configuration?

Yes, the BQ29405DCT3 supports 2-, 3-, and 4-cell configurations. In 2-cell mode, VC1 and VC2 are shorted together and connected to the high-side of the stack, VC3 connects to the mid-point, and VC4 connects to the low-side. The BQ29405DCT3's four independent sense inputs allow flexible routing without external resistors or switches.

What is the maximum allowable voltage on the VC pins of the BQ29405DCT3?

The absolute maximum rating for VC1, VC2, VC3, and VC4 pins of the BQ29405DCT3 is –0.3 V to 28 V referenced to GND. This 28 V headroom accommodates full 4S Li-ion stacks (≤16.8 V) plus transient margins and ensures robustness against load-dump or inductive kick events in portable systems using the BQ29405DCT3.

Does the BQ29405DCT3 require external components to operate?

Yes, the BQ29405DCT3 requires at minimum an external capacitor on the CD pin to set delay time and an N-channel MOSFET driven by the OUT pin to interrupt the battery pack's positive rail. Optional RC filters (RIN/CIN on each VC pin, RVD/CVD on VDD) improve noise immunity. No external reference or calibration components are needed - the BQ29405DCT3 integrates all precision voltage references internally.