Host-Side Single Cell Lithium Battery Gauge


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The RT9420 is a compact, host-side fuel gauge IC for lithium-ion (Li+) battery-powered systems.

For the embedded Fuel Gauge function, the state-of-charge (SOC) calculation is based on the battery voltage information and the dynamic difference between battery voltage and relaxed OCV, by using iteration to estimate the increasing or decreasing SOC.

Voltage-based algorithm can support smoothly SOC and does not accumulate error with time and current. That is an advantage compared to coulomb counter which suffer from SOC drift caused by current-sense error and battery self-discharge. The disadvantage of voltage-based fuel gauge, it can report incremental SOC(%), but can't report capacity (mAh).

A quick sensing operation provides a good initial estimate of the battery's SOC. This feature allows the IC to be located on system side, reducing cost and supply chain constraints on the battery. Measurement and estimated capacity data sets are accessed through an I2C interface.

The RT9420 is available in the WDFN-8L 2x3 package.


  • Smartphones
  • Tablet PC
  • Digital Still Cameras
  • Digital Video Cameras
  • Handheld and Portable Applications
Key Spec.
Status Active
Number of Series Cells 1
Supply Voltage (min) (V) 2.5
Supply Voltage (max) (V) 4.5
Communication Interface I2C
Package Type WDFN2x3-8
  • Host-Side Fuel Gauging
  • Precision Voltage Measurement ±12.5mV Accuracy
  • Accurate Relative Capacity (RSOC) Calculated from Voltaic Gauge Algorithm with Temperature Compensation
  • No Accumulation Error on Capacity Calculation
  • No Battery Relearning Necessary
  • No Current Sense Resistor Required
  • External Alarm/Interrupt for Low Battery Alert
  • I2C Compatible Interface
  • Low Power Consumption
TitleLast UpdateShareDownload
Host-Side Single Cell Lithium Battery Gauge2015/05/19
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Additional Documents
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Power Management Components for Lithium-Ion Battery Powered Applications