Battery Gauge Highly accurate State-of-Charge measurement

In many battery applications it is important to know how much charge is left in the battery.

Conventional Coulomb Counting Method

Checking the state of charge (SOC) of Li-Ion cells is often done by coulomb counting method. These methods are accurate in theory, but suffer from accumulation errors over time. In addition, the circuit is complicated due to the current sense circuit.

Richtek Solution

An alternative way to determine the SOC is using a dynamic voltage based battery gauge, which measures the battery voltage over time, and uses the dynamic voltage measurements in combination with a battery model to calculate the relative SOC. This topology does not suffer from error accumulation, and is used in RT9420 and RT9428 battery gauge ICs.

These ICs are simply connected to the battery terminals, and monitor the battery voltage very accurately. They use an internal algorithm to calculate the relative SOC and communicate it back to the host microcontroller via I²C.

For best SOC accuracy, the application battery pack needs to be characterized during design stage, and battery specific compensation as well as temperature and charge/discharge effects can be included in the SOC calculation.

Product	Key Features	P/N
I2C Host-side Single Cell Li-ion Battery gauge	±2% State-of-Charge (SOC) error under general charging/discharging Precise 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 and no current sense resistor required WDFN-8L 2x3 package	RT9420
I2C Host-side Single Cell Li-ion Battery gauge	±2% State-of-Charge (SOC) error under general charging/discharging Precise voltage measurement ±7.5mV accuracy Accurate relative capacity(RSOC) calculated from Voltaic Gauge algorithm with temperature compensation No accumulation error on capacity calculation No battery relearning necessary and no current sense resistor required WL-CSP-8B 1.6x1.52 (BSC) package	RT9428