This product is a full cell-temperature sensing and high cell-voltage accuracy Lithium-ion:
- 32 battery pack
- cost-effective
- high-capacity
- ± 1.5mV voltage accuracy at 25°C without calibration
- Balancing up to 100mA, support external balacing circuit
- Full cell-temperature sensing with MUX
- Robust and programmable battery cell and pack protectionPack protection
- Robust daisy-chain communication with data reclocking and ring architecture
- 15uA in shutdown mode
- Isolate UART interface for microcontroller and CAN network communication
- Battery energy storage system
- Other industrial battery pack (>10S)
- This is block diagram of system:
| Device | BQ79616 | TMUX1574 | TMUX1308 |
|---|---|---|---|
| Feature | Monitor voltage and temperature; Protect overvoltage, undervoltage, overtemperature | Expand GPIO4 through GPIO7 of BQ79616 to an external SPI EEPROM (restores pack information) | Expand temperature-sensing of BQ79616 from 8 channel to 16 channel |
| Pins | 8xGPIO for temperature sensing and 16xVC for voltage sensing | a TMUX1308 connect one at a time to the TSREF output pin of BQ79616 |
Note:
- TSREF is set at a high or low level
- The BCU then polls the MUX channels and determines if the voltage reported on the MUX channel connected to TSREF matches the TSREF pin output -> MUX is stuck on a specific channel or reporting voltages corresponding to incorrect channels
- GPIO8 of BQ79616 is reserved for humidity sensor interface.
- CVDD pin on BQ79616 is used to supply power to the TMUX1308, TMUX1574, external EEPROM and humidity sensor -> This is cause leakage current to external load when the BQ79616 is in SHUTDOWN mode -> Using TPS22810 is ennabled by GPIO3 of BQ79616 and the device is used to switch the power supply output from CVDD to prevent unintended leakage current.
- BQ79616 supports the UART interface to the MCU
- ISO7742 is placed between the BQ79616 and MCU to isolate the TX and RX pins of each device. Since the TX and CVDD pins of the BQ79616 are constanton power supply, These pins can cause leakage current to the ISO8842 in SHUTDOWN mode PMOS TMUX1102, and optocoupler are used to block the leakage current -> To initiate UART communication, the MCU, needs enable the optocoupler to switch on the PMOS and TMUX1102 from MCU side.
- This design also uses a BJT network for external passive cell balancing, have internal resister can support up to 100mA of balancing current. -> The voltage across the internal passive cell balancing resistors are used to switch ON the external BJTs for passive cell balancing.
- To isolate communication, the design uses two high-voltage capacitors for daisy chain communication between two BQ79616 and two transformers in daisy chain communication between the BMUs or the BCU.
This image is showing the strategy of reading all thermistors and cell voltages.
Detail:
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2x TMUX1308 are used to multiplex 16 Negative Temprature Coefficient (NTC) thermistors to one BQ79616 -> Using three pins GPIO (GPIO5, GPIO6, GPIO7) to address the 8 NTC thermistor channels of TMUX1308 - 5 GPIOs can switch 16 NTC thermistor, if more thermistors are required, 6 GPIOs can switch 24 NTC thermistors.
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And now, we can easily increased using the TMUX1308 or other multiplexer.
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The loop of NTC thermistor switching consists of a broadcast write to all stacked BQ79616 GPIO5 to 7 pins / broadcast read of the TSREF and GPIO1 to GPIO2. -> This design need 8 loop for 16 NTC thermistors. **The number of stacked BMUs is N, using BQ796xx:
| time write in loop (us) | time read in loop (us) |
|---|---|
| (14 + 4 × 2 × N_BMU − 1 + 60) | (14 + 4 × 2 × N_BMU − 1 + 60 + 14 + 4 × 2 × N_BMU − 1 + 90 × 2 × N_BMU) |
Standard GBT34131-2023 (100ms for VCELL and 1s NTC thermistors)
Ex: BESS rack voltage = 1500V, one rack consists of 470 pieces of battery cells (psc) in series -> using 15 BMUs (30 BQ79616 divices) to monitor all battery cells. -> One loop to read temperature data is 4.11ms (BQ79616 read BQ79616); Read temperature of all 16 (8 couple) NTC thermistors is 4.11 x 8 = 38.88ms; 11.706ms is required to read the cell voltage (VCELL) data of all stacked BQ79616 devices. -> Total time for 1500V rack: 4.11 + 38.88 + 11.706 = 44ms.
- Using FET to achieve 100mA balancing current
- CB block decreate from 3.5V input to 3.3V output
- To achieve 100mA white CB voltage is 3.5V, Rcb6 = Rcb5 = 15(Ohm).
- When using NPN transistor, Rb needs two condition:
1. NPN transistor work in the saturation region for a small heat dissipation area.
2. UBE > UBE(on), UBE(on) must be smaller than the voltage across the Rcb5 and as small as possible to enable an easy selection of Rb.
This design using Rb = 300 Ohm can support cell balancing current up to 600mA.
BQ79616 support both the forward and reverse communication direction.
- BCU issues pings to the BQ79600 using SPI interface.
- Pings are non-comm signals for simple actions (WAKE and SHUTDOWN mode).
- BQ7900 can send and receive tones to and from the stacked BQ79616 in the North and South in a duty cycle.
- Considering the GBT34131-2023 standards, the voltage cycle need to be less than 100ms,and the temperature cycle ness to be less than 1s.
The design reserves an isolated UART interface to the MCU for a CAN structure.
-> ISO7742 is used connect the UART interface of BQ9616 and the MCU
- TMUX1102 is used to block the current from the TX pin (powered-off protection, and high bandwidth of 300 MHz)
- Both TMUX1102 and PMOS are enabled by an optocoupler pulldown signal controlled by th MCU.
All other information reference to Design_Guide.pdf
In this project, I use Kicad 7.0 for layout and design.
(UPDATE LATE)
(UPDATE LATE)
All information reference at Schematic.pdf
All test result reference at Design_Guide.pdf