2 Theory of Operation

The BQ79631-Q1 is designed to verify the safe operation of charging, discharging, and power transfer to a load in an EV/HEV system. Various voltage sense measurements are made at critical nodes within the BJB/BDU to make sure that the vehicle is operating as intended at all times. In a typical BMS system, a BQ79631-Q1 is used to gather critical data in the following areas:

• HV ±
• Link ±
• Charge ±
• HV_Fuse
• HV_Extra1_Plus/HV_Extra2_Plus

The typical BMS system with stacked modules has three main sub-systems, as shown in Figure 2-1:

• Host controller - in this case a TMS570 LaunchPad?.
• A BQ79631-Q1 configured as an isolated communication bridge device - a BQ79600EVM , BQ79616EVM, or a BQ79631EVM can also support this .
• BQ79616EVM based modules attached to cells - these can be stacked up to 35 total devices (including the bridge device).

Figure 2-1 Typical BMS System with Stacked Modules

All commands and data are communicated with a host through either a UART or daisy-chain communication connection. The BQ79631 remains idle until a command is received from the host. The BQ79631 can support a host PC or microcontroller (through the UART connection header) or a daisy-chain interface from a BQ79600 implemented as a communication bridge.

The typical flow is for the host to go through the following simplified sequence:

1. Wakeup the BQ79631EVM board by sending a WAKEUP pulse when using the UART interface, or send a WAKE tone when using the BQ79631EVM in a stack with other BQ79616EVM boards for a large battery pack. (Typically an auto address signal is needed if using the BQ79631EVM in a stack of other BQ devices but is not needed if using a single BQ79631EVM).
2. Send a sample command to the BQ79631-Q1 to read the voltage measurement results.
3. If no stop command is sent, then the BQ79631-Q1 has a built-in timeout (set by the user), after which time the discharge is stopped automatically.
4. The host can then decide to repeat the process (back to step 2) or send commands to shutdown the BQ79631EVM and return later.