Year: 2025

BQ24728 Datasheet – Battery SMBus Charge Controller – TI

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Part Number: BQ24728, BQ728, BQ24728RGRT

Function: Battery SMBus Charge Controller ( Power management , System Charge Power IC )

Package: QFN 20 Pin

Manfacturers: Texas Instruments

Image:

BQ24728 image

Description

The bq24728 is a high-efficiency, synchronous battery charger, offering low component count for space-constraint, multi-chemistry battery charging applications. The device uses two charge pumps to  separately drive n-channel MOSFETs (ACFET, RBFET and BATFET) for automatic system power source selection. SMBus controlled input current, charge current, and charge voltage DACs allow for high regulation accuracies that can be programmed by the system power management micro-controller.

Features

  • SMBus programmable charging parameters (voltage/current/input limit)
  • High-efficiency synchronous charging architecture
  • Automatic power source selection (adapter ↔ battery)
  • Supports multi-chemistry battery systems (primarily Li-ion/Li-polymer)
  • Low external component count
  • High regulation accuracy via internal DACs
  • Dual charge pump for full NMOS drive (no P-channel needed)

Pinout

BQ24728 Datasheet, Pinout

Typical Circuit Usage

  • Adapter input → ACFET/RBFET → system rail
  • Synchronous buck stage → battery charging path
  • BATFET controls battery connection/disconnection
  • SMBus connected to EC (Embedded Controller)

Design Notes (Critical Points)

  • Accurate current sensing resistor selection is essential for charge precision
  • External MOSFET selection impacts efficiency and thermal performance
  • SMBus firmware must properly configure charging profiles
  • PCB layout must minimize switching loop inductance
  • Thermal design critical for high-current charging scenarios

Applications

  • Notebook / ultrabook / netbook platforms
  • Handheld and portable terminals
  • Industrial battery-powered equipment
  • Medical portable systems
  • Embedded battery charging modules

Advantages

  • Highly flexible and programmable
  • Efficient power-path control
  • Reduced component count
  • Suitable for smart battery systems

Alternative / Equivalent Products

  • BQ24727 (closely related variant)
  • BQ24725A
  • ISL6255
  • MAX8734
  • LTC4012

BQ24728 Datasheet

BQ24728 pdf

BQ24725 Datasheet

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2N449 PDF Datasheet – Transistor, NPN, 15V, -20mA, TO-39

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Part Number: 2N449

Function: 15V, -20mA, NPN Transistor.

Package: 3-Pin TO-39 Type

Manufacturer: New Jersey Semiconductor

Images:

2N449 datasheet pdf

Description

The 2N449 is a low-power bipolar junction transistor rated for 15V operation and a maximum collector current of -20mA, typically used in small-signal applications. It offers modest power dissipation and is suitable for low-level amplification and switching tasks in compact electronic designs. This transistor is commonly applied in signal processing, low-current switching, and general-purpose analog circuits.

Features

  • Low power dissipation of 65mW
  • Suitable for small-signal amplification
  • Compact and efficient for low-current circuits
  • Stable operation within limited temperature range

Absolute Maximum Ratings (Tc = 25 °C)

Parameter Symbol Value Unit
Collector-Base Voltage VCBO 15 V
Emitter-Base Voltage VEBO 15 V
Collector Current IC -20 mA
Collector Power Dissipation PC 0.065 W
Junction Temperature Tj 85 °C
Storage Temperature Tstg -55 to 85 °C

Design Notes

  • Ensure collector current remains within 20mA to avoid device damage
  • Suitable for low-power circuits with minimal heat generation
  • Biasing must be carefully designed for stable small-signal amplification
  • Limited thermal range requires controlled operating environment
  • Not suitable for high-frequency or high-power applications

Typical Circuit Usage

  • Low-level signal amplification
  • Small current switching circuits
  • Sensor interface stages
  • Pre-amplifier circuits
  • Basic transistor switching applications

How to Choose This Part

  • Select for low-voltage, low-current applications
  • Ideal for compact and low-power analog designs
  • Ensure thermal limits are not exceeded in operation
  • Use where high gain or power handling is not critical
  • Consider alternatives for wider temperature or higher current needs

Applications

  • Signal processing circuits
  • Low-power electronic devices
  • Instrumentation circuits
  • Educational and prototyping designs
  • Embedded analog interfaces

Alternative / Equivalent Products

  • 2N3904 (general-purpose NPN transistor)
  • BC547 (low-noise small-signal transistor)
  • 2N2222 (higher current alternative)
  • PN2222A (plastic package variant)
  • BC548 (similar small-signal transistor)

2N449 Datasheet

2N449 pdf