Texas Instruments BQ75614-Q1, User Manual

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2 Theory of Operation - Stackable BQ79616EVM
Figure 2-1 shows the system stack diagram.
Figure 2-1. System Block Diagram - BQ79616
The BMS system is designed to prolong the useful life of lithium-ion cells in battery packs through passive
balancing. The battery pack is broken into a series of modules, each of which contains up to 16 cells. This
system will monitor voltages of individual battery cells and dissapate individual cell voltages through the use of
internal CB FETs. The BMS allows battery-powered electric machines to use smaller battery packs and use
fewer charging cycles to perform the same amount of work. It also improves the overall lifetime of Li-ion battery
packs by preventing under- and overvoltage damage from occurring.
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 BQ79616-Q1 configured as an isolated communication bridge device - a BQ79600EVM or another
BQ79616EVM can support this
• BQ79616EVM based modules attached to cells - these can be stacked up to35 total (including the bridge
device)
All commands and data are communicated with a host via either a UART or daisy-chain communication
connection. The BQ79616 will remain idle until a command is received from the host. The BQ79616 can support
a host PC or microcontroller (via the UART connection header) or a daisy-chain interface from a BQ79616-Q1
implemented as a communication bridge.
The typical flow is for the host to go through the following simplified sequence:
1. Wakeup the BQ79616EVM board by sending a WAKEUP pulse when using the UART interface, or sending a
WAKE tone when using the BQ79616EVM in a stack of other BQ79616EVM boards for a large battery pack
or a BQ79616-Q1 configured as a bridge. Initialize the BQ79616-Q1 to be ready for use.
2. Send a sample command to the BQ79616-Q1 to read the cell measurement results.
3. The host will use the cell measurement data to calculate an average and determine the highest or lowest
cells and determine the cells that should be balanced.
4. If no stop command is sent, the BQ79616-Q1 has a built-in timeout (set by the user), after which time the
discharge will be stopped automatically.
www.ti.com Theory of Operation - Stackable BQ79616EVM
SLUUC37B – JULY 2019 – REVISED OCTOBER 2020
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