SMBus/I2C Interoperability for Battery Packs and Notes on System Implementation
The following information may be helpful in understanding compatibility of SMBus batteries with embedded and computer systems. Some systems may need to incorporate both I2C and SMBus devices. GlobTek offers a wide range of product offering in Lithium Ion and NIMH battery packs with integrated communications.
Smart Battery System (SBS):
- The industry standard for communication between battery packs and customer systems is the Smart Battery System (SBS). SBS contains over 100 commands, ranging from Remaining Capacity to Manufacturer Info to State of Health.
- SBS is implemented using the SMBus protocol. SMBus is a command-oriented protocol. A typical SMBus interaction may look like following:
- Address byte: Master says, “Attention Battery, I’m talking to you!”
- Command byte: Master says, “Battery, please send me your Remaining Capacity.”
- Data byte: Battery replies by writing Remaining Capacity to the data line
I2C vs. SMBus
- I2C and SMBus are both serial protocols which use two wires (+ground). Wire 1: Data, Wire 2: Clock. From a hardware perspective, they are essentially identical.
- From a protocol perspective, SMBus is a stricter implementation of I2C. SMBus specifies a set of commands and an exact format for master-slave interaction. The I2C protocol does not define a structure for interaction.
- If a system contains multiple I2C devices, and an SMBus battery, typically all of those devices can co-exist on the same bus, but the responsible engineer needs to mindful of the way the system master interacts with each device.
- Additionally, all bus timing should comply with SMBus specifications, if I2C and SMBus devices (slaves and/or masters) are used together.
- Clock rate:
- I2C: 0 - 3.4MHz
- SMBus: 10KHz – 100KHz (SMBus 3.0 allows up to 1MHz)
- Clock stretch time out:
- I2C: No, indefinite clock stretch allowed
- SMBus: Yes, timeout after 35ms
GlobTek offers standard off the shelf battery packs which can be seen at this link: https://en.globtek.com/battery-packs/#models_table
Customized battery pack solutions are available upon request.