The RT9451 integrates a high efficiency USB friendly switch mode charger with On-The-Go (OTG) support for single cell Li-ion and Li-polymer batteries, D+D- detection, and a 50mA LDO regulator into a single chip.

The charger features a synchronous 375kHz PWM controller with integrated power MOSFETs, input current sensing and regulation, Minimum Input Voltage Regulation (MIVR), high accuracy charge current and voltage regulation, and charge termination. It charges the battery in three phases : low current pre-charge, constant current fast charge, and constant voltage trickle charge. The input current is automatically limited to the value set by the host. The charger can be configured to terminate charge based on user-selectable minimum current level and automatically restart the charge cycle if the battery voltage falls below the recharge threshold. A safety timer with reset control provides a safety backup for I2C interface. The charger automatically enters sleep mode or high impedance mode when the input supply is removed. The charge status is reported to the host using the I2C interface and the STAT pin. The D+D- detection circuit allows automatic detection of a USB wall charger. If a wall charger is detected, the input current limit will automatically increase from 500mA to 975mA.

In OTG mode, the PWM controller boosts the battery voltage to 5V and provides up to 1.6A of current to the USB output. At very light load, the Boost operates in burst mode to optimize efficiency. OTG mode can be enabled either through I2C interface or GPIO control.


  • Mobile Phones and Smart Phones
  • MP3 Players
  • Handheld Devices
Key Spec.
Status NRND
Recommended Alternative  RT9467
Vin (min) (V) 4.3
Vin (max) (V) 12
Battery Charge Voltage (max) (V) 4.44
Battery Charge Current (max) (A) 4
Status Indicator Yes
Charger Type Switching
Input Source AC Adapter;USB
Features Adjustable Current Limit;Built-in Bootstrap Switch;Current Mode Control;Cycle-by-Cycle Current Limit;I2C;Internal Compensation;OCP;OVP;UVP
Package Type WQFN4x4-32
Built-in Power MOSFETs Yes
  • Integrated Switching Charger and 50mA LDO in a Single Package
  • Charges Faster Than Linear Chargers
  • High Accuracy Voltage and Current Regulation
    ► Charge Voltage Regulation Accuracy : ±1%
    ► Charge Current Regulation Accuracy : ±5%
  • Minimum Input Voltage Regulation : 4.2V to 4.76V with Step of 80mV
  • Bad Adaptor Detection and Rejection
  • Safety Limit Register for Maximum Charge Voltage and Current Limiting
  • High Efficiency Mini-USB/AC Battery Charger for Single Cell Li-Ion and Li-Polymer Battery Packs
  • 28V Absolute Maximum Input Voltage Rating
  • 12V Maximum Operating Input Voltage
  • Built-In Input Current Sensing and Limiting
  • Integrated Power FETs for Up to 4A Charge Rate
  • Programmable Charge Parameters through I2C Interface (up to 400 Kbps) :
    ► Input Current
    ► Fast Charge/Termination Current
    ► Charge Voltage (3.5V to 4.44V)
    ► Safety Timer
    ► Termination Enable
  • Synchronous Fixed Frequency PWM Controller Operating at 375kHz With 0% to 99% Duty Cycle
  • Automatic High Impedance Mode for Low Power Consumption
  • Safety Timer with Reset Control
  • Thermal Regulation and Protection
  • Input/Output Over-Voltage Protections
  • Status Output for Charging and Faults
  • USB Friendly Boot-Up Sequence
  • Automatic Charging
  • Boost Mode Operation for USB OTG
    ► Input Voltage Range (BATS) : 2.5V to 4.5V
    ► Output Voltage for VIN : 4.425V to 5.506V
  • RoHS Compliant and Halogen Free
TitleLast UpdateDownload
Switch-Mode Single Cell Li-ion Battery Charger with USB OTG2013/07/05
Additional Documents
Title Last Update ShareDownload
Power Management Components for Lithium-Ion Battery Powered Applications
Part NumberPackage TypePackage Qty.Free SampleBuy From Authorized Distributor
RT9451GQWWQFN4x4-321500 Request Buy from Distributor