With the increasing popularity of portable devices, lithium-ion (Li-ion) batteries have become ubiquitous. These batteries, however, have stringent safety requirements which typically require battery packs with integrated protectors.
The characteristics of Li-ion batteries also often warrant battery fuel gauges to accurately report state-of-charge (SOC) under various operating and environmental conditions. Depending on the type of applications, the system may be designed with a host-side fuel gauge (Figure 1) or a pack-side fuel gauge (Figure 2). A host-side fuel gauge resides on the host system and is connected to the application processor, while a pack-side fuel gauge resides on the battery pack and is connected to the Li-ion cell.
In the pack-side approach, the proximity of the cells to the fuel gauge results in a number of unique advantages:
- The fuel gauge, battery protector, and even authentication can be integrated in a single, tiny solution.
- It improves the accuracy of SOC reporting by eliminating the effect of the connector resistance for voltage and current measurements.
- The fuel gauge typically includes a die temperature sensor to monitor the cell (if close to the IC) as well as protection FETs and can eliminate the need for a separate sensor for the cell temperature. Alternately, the fuel gauge can also measure temperature of a cell further away using a thermistor.
- The battery connector can be made smaller, as fewer connections and measurements need to be routed to the host side.
Maxim's MAX17301/11 fuel gauge with protector and SHA-256 authentication (Figure 3) is an example of a solution that simplifies pack-side fuel-gauge implementation. The IC integrates a 2-level protector and SHA-256 authentication to the industry's most accurate battery fuel gauge. MAX17301/11 offers the following features that are useful for pack-side fuel gauging:
- ModelGauge m5 algorithm that combines short-term accuracy and linearity of a coulomb counter with long-term stability of a voltage-based fuel gauge to provide industry-leading fuel gauge accuracy
- SHA-256 authentication to prevent use of unsafe counterfeit batteries
- Automatic compensation for cell aging, temperature, and discharge rate, with accurate SOC over a wide range of operating conditions
- Electronic serialization for traceability of battery packs
So, for your next Li-ion battery-based design, consider a pack-side fuel-gauge implementation. The battery—and the device user—might just thank you for this!