3 Theory of Operation
The BQ79631-Q1 is designed to ensure the safe operation of charging, discharging, and power transfer to load
in an EV/HEV system. Various voltage sense measurements are made at critical nodes within the BJB/BDU to
ensure that the vehicle is operating as intended at all times. In a typical BMS system, a BQ79631-Q1 will be
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
:
• 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 (including the bridge
device)
Figure 3-1. Typical BMS System with Stacked Modules
All commands and data are communicated with a host via either a UART or daisy-chain communication
connection. The BQ79631 will remain idle until a command is received from the host. The BQ79631 can support
a host PC or microcontroller (via 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 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, the BQ79631-Q1 has a built-in timeout (set by the user), after which time the
discharge will be stopped automatically.
Theory of Operation
8
BQ79631EVM Evaluation Module
SLUUCC3 – FEBRUARY 2021
Copyright © 2021 Texas Instruments Incorporated
