3.5. Slave 18-Cell
v1.1.3 and above¶
The following description only applies for the 18-cell BMS-Slave Board hardware versions
1.1.3 and above.
All connector pinouts described below follow the Convention for Connector Numbering.
220.127.116.11. Block Diagram¶
18.104.22.168. Schematic and Board Layout¶
More information about the board schematic and layout files can be found in section Design Resources.
The following general descriptions apply to both, the primary and the secondary unit on the foxBMS BMS-Slave. If there are any differences in hardware between the primary and the secondary unit they will be marked as such.
22.214.171.124. Cell Voltage Measurement¶
The cell voltage sense lines are input on the connector X200. The pinout is described in table 3.25.
|1||VBAT-||Input||Battery module negative terminal|
|2||CELL_0+||Input||Cell 0 positive terminal|
|3||CELL_2+||Input||Cell 2 positive terminal|
|4||CELL_4+||Input||Cell 4 positive terminal|
|5||CELL_6+||Input||Cell 6 positive terminal|
|6||CELL_8+||Input||Cell 8 positive terminal|
|7||CELL_10+||Input||Cell 10 positive terminal|
|8||CELL_12+||Input||Cell 12 positive terminal|
|9||CELL_14+||Input||Cell 14 positive terminal|
|10||CELL_16+||Input||Cell 16 positive terminal|
|11||VBAT+||Input||Battery module positive terminal|
|13||CELL_0-||Input||Cell 0 negative terminal|
|14||CELL_1+||Input||Cell 1 positive terminal|
|15||CELL_3+||Input||Cell 3 positive terminal|
|16||CELL_5+||Input||Cell 5 positive terminal|
|17||CELL_7+||Input||Cell 7 positive terminal|
|18||CELL_9+||Input||Cell 9 positive terminal|
|19||CELL_11+||Input||Cell 11 positive terminal|
|20||CELL_13+||Input||Cell 13 positive terminal|
|21||CELL_15+||Input||Cell 15 positive terminal|
|22||CELL_17+||Input||Cell 17 positive terminal|
Each of these lines is fused with a fast acting 250 mA surface-mount fuse (F301 - F319) on the board except of the VBAT+ and VBAT- lines which are fused with a value of 500 mA (F300 and F320). This essentially is important for an evaluation environment. The VBAT+ and VBAT- connection is used for the internal power supply of the slave board. If the battery module does not contain these separate wires to the positive and negative module terminal the solder jumpers SJ300 and SJ301 have to be shorted. In this case the slave will be supplied through the sense lines CELL_0- and CELL_11+. Running the slave in this configuration could result in cell measurement errors due to voltage drop on the sense wires.
The cell input lines are filtered by a grounded or differential capacitor filter (both possibilities provided on the PCB). More information on the corner frequency of this filtering can be found in the schematic. The grounded capacitor filter should be used in environments affected with high noise as it offers a high level of battery voltage ripple rejection. The differential capacitor filter can be used when noise is less occurrent or the design is subjected to cost optimization.
126.96.36.199. Passive Cell Balancing¶
The passive balancing circuit is realized by a parallel connection of two 130 Ohm discharge-resistors that can be connected to each single cell in parallel. The MOSFET switches (T1500 - T1517) that control the connection to the cells are controlled by the primary LTC6813-1 monitoring IC. The LTC6813-1 on the secondary unit does not support balancing. The resistor value of 2x 130 Ohm results in a balancing current of about 55mA at a cell voltage of 3.6V. This current results in a power dissipation of about 0.2W per balancing channel (at 3.6V).
188.8.131.52. Global Cell Balancing Feedback¶
In order to check the proper function of the balancing process or to detect a malfunction in the balancing control circuit, a global balancing feedback signal is connected to the LTC6813-1. This allows the system to check whether any balancing action is currently taking place at any time. The feedback signal is connected to the GPIO3 of the LTC6813-1. The signal remains in a logic zero state until any balancing action on any cell starts.
184.108.40.206. Temperature Sensor Measurement¶
The cell temperature sensors are connected to the connectors X201 (primary) and X202 (secondary). The pinout is identical for the primary and secondary unit and is described in table 3.26.
|1||T-SENSOR_0||Input||NTC Sensor 0 terminal 1|
|2||T-SENSOR_1||Input||NTC Sensor 1 terminal 1|
|3||T-SENSOR_2||Input||NTC Sensor 2 terminal 1|
|4||T-SENSOR_3||Input||NTC Sensor 3 terminal 1|
|5||T-SENSOR_4||Input||NTC Sensor 4 terminal 1|
|6||T-SENSOR_5||Input||NTC Sensor 5 terminal 1|
|7||T-SENSOR_6||Input||NTC Sensor 6 terminal 1|
|8||T-SENSOR_7||Input||NTC Sensor 7 terminal 1|
|9||FUSED_VBAT-||Input||NTC Sensor 0 terminal 2|
|10||FUSED_VBAT-||Input||NTC Sensor 1 terminal 2|
|11||FUSED_VBAT-||Input||NTC Sensor 2 terminal 2|
|12||FUSED_VBAT-||Input||NTC Sensor 3 terminal 2|
|13||FUSED_VBAT-||Input||NTC Sensor 4 terminal 2|
|14||FUSED_VBAT-||Input||NTC Sensor 5 terminal 2|
|15||FUSED_VBAT-||Input||NTC Sensor 6 terminal 2|
|16||FUSED_VBAT-||Input||NTC Sensor 7 terminal 2|
Standard 10kΩ NTC resistors (e.g. Farnell-Nr. 1299926) are recommended for use. When using other values than these, the series resistors (R100-R107) on the board may have to be adjusted. Please note that the accuracy of the internal voltage reference VREF2 decreases heavily with a load of over 3mA. Using 8x 10kΩ NTC resistors with the corresponding 10kΩ series resistors results in a current of 1.2mA (at 20°C) which is drawn from VREF2.
Each 8 temperature sensors are connected to an analog multiplexer. The analog multiplexer can be controlled via I²C by the LTC6813-1 (7-bit address: 0x4C). In order to ensure fast settling times after switching the multiplexer input, the output signal of the multiplexer is buffered by an operational amplifier. Finally the analog voltage of the selected sensor is measured on the GPIO1 pin of the LTC6813-1.
220.127.116.11. On-board EEPROM¶
The primary unit as well as the secondary unit of the foxBMS BMS-Slave board is equipped with an EEPROM IC (IC801). The EEPROM for example can be used for storing data such as calibration values. Similar to the analog multiplexers, the EEPROM device is connected to the I²C bus of the LTC6813-1 (7-bit address: 0x50).
18.104.22.168. On-board Ambient Temperature Sensor¶
For an additional monitoring of the ambient temperature an on-board temperature sensor is used. This temperature sensor can be read by the LTC6813-1 via the I²C bus (7-bit address: 0x48). It is possible to program an alert temperature. Once the measured temperature reaches this alert temperature the alert pin of the IC is set to a logic low level. Currently this signal is not used on the BMS-Slave board, but it is accessible on the connector X404.
22.214.171.124. Additional Inputs and Outputs¶
Several additional analog and digital inputs and outputs are provided on the BMS-Slave board via pin headers. Each 16 analog inputs are provided on connector X400 (primary) and X401 (secondary). The pinout for the connectors for the primary and secondary unit is identical and is described in table 3.27.
|1||ANALOG-IN_0||Input||Analog input 0|
|2||ANALOG-IN_1||Input||Analog input 1|
|3||ANALOG-IN_2||Input||Analog input 2|
|4||ANALOG-IN_3||Input||Analog input 3|
|5||ANALOG-IN_4||Input||Analog input 4|
|6||ANALOG-IN_5||Input||Analog input 5|
|7||ANALOG-IN_6||Input||Analog input 6|
|8||ANALOG-IN_7||Input||Analog input 7|
|9||ANALOG-IN_8||Input||Analog input 8|
|10||ANALOG-IN_9||Input||Analog input 9|
|11||ANALOG-IN_10||Input||Analog input 10|
|12||ANALOG-IN_11||Input||Analog input 11|
|13||ANALOG-IN_12||Input||Analog input 12|
|14||ANALOG-IN_13||Input||Analog input 13|
|15||ANALOG-IN_14||Input||Analog input 14|
|16||ANALOG-IN_15||Input||Analog input 15|
|17||+3.0V_VREF2||Output||LTC6813-1 3.0V voltage reference|
Each 8 analog inputs are connected to an analog multiplexer. The analog multiplexers can be controlled via I²C by the LTC6813-1 (7-bit addresses: 0x4D and 0x4E). In order to ensure fast settling times after switching the multiplexer input, the output signals of the multiplexers are buffered by operational amplifiers. Finally the analog voltage of the selected sensor can be measured on the GPIO2 pin of the LTC6813-1.
Each 8 digital inputs/outputs are provided on the connectors X402 (primary) and X403 (secondary). The pinout for the connectors for the primary and secondary unit is identical and is described in table 3.28.
|1||DIGITAL-IO_0||Input/Output||Digital input/output 0|
|2||DIGITAL-IO_1||Input/Output||Digital input/output 1|
|3||DIGITAL-IO_2||Input/Output||Digital input/output 2|
|4||DIGITAL-IO_3||Input/Output||Digital input/output 3|
|5||DIGITAL-IO_4||Input/Output||Digital input/output 4|
|6||DIGITAL-IO_5||Input/Output||Digital input/output 5|
|7||DIGITAL-IO_6||Input/Output||Digital input/output 6|
|8||+5.0V_VREG||Output||LTC6813-1 5.0V regulated voltage|
Each 8 digital inputs/outputs are connected to an I²C controlled port expander (7-bit address: 0x20). The direction of the inputs/outputs as well as the logic levels on the pins can be selected by register settings. Each of the 8 digital inputs/outputs has a discrete pull up resistor that for example can be used for directly connecting a tactile switch.
126.96.36.199. isoSPI Daisy Chain Connection¶
The data transmission between the slaves and between the slaves and the basic board takes place using the isoSPI interface. The isoSPI signals are input/output on the connectors X500/X501 (primary) and X502/X503 (secondary). The isoSPI ports are bidirectional, that means they can be used in forward and reverse direction. The isoSPI connections are isolated galvanically using pulse transformers (TR1400). The voltage amplitude of the differential signal can be adjusted by setting resistors (see section Daisy Chain Communication Current).
|Connector Pin||Daisy Chain|
|1||IN+ (Primary/Secondary LTC6813-1)|
|2||IN- (Primary/Secondary LTC6813-1)|
|Connector Pin||Daisy Chain|
|1||OUT+ (Primary/Secondary LTC6813-1)|
|2||OUT- (Primary/Secondary LTC6813-1)|
188.8.131.52. Hardware Settings / Options¶
184.108.40.206.1. Software Timer¶
The internal software timer of the LTC6813-1 can be enabled/disabled by a dedicated external pin (SWTEN, pin 36 of the LTC6813-1). In order to support all features, the foxBMS BMS-Slave board offers a possibility to switch the software timer. The software timer is enabled in the standard configuration, which means pin 36 is pulled to VREG via a zero-ohm resistor (R1407). The timer can be disabled by removing the resistor R1407 and placing a zero-ohm resistor to R1406.
220.127.116.11.2. Daisy Chain Communication Current¶
The daisy chain communication current can be set by the resistors R1400 and R1402. The default value is 820Ω for R1402 and 1.2kΩ for R1400. This values result in a bias current of approx. 1mA and a differential signal amplitude of 1.18V. Theses values are suitable for high noise environments with cable lengths of over 50m. For more information please have a look at the LTC6813-1 datasheet.
18.104.22.168.3. Status LED¶
The status LEDs LD1400 show the current mode of each, the primary and secondary LTC6813-1. The LED is on in STANDBY, REFUP or MEASURE mode, whereas the LED is off in SLEEP mode. The LED can be disabled by removing the resistor R1403 next to the LED.
22.214.171.124.4. GPIO Extension Connector¶
The internal GPIO lines 1 to 5 of the primary or secondary LTC6813-1 can be connected to the GPIO extension pin header X404 via optional zero-ohm resistors. In the standard configuration these resistors are not placed. Of course it is possible to place each both resistors for a parallel connection of the internal signals to the GPIO extension connector. For more information see the corresponding page of the schematics. The placement of the resistors and the resulting connection is shown in table 3.31.
|GPIO||connect to pin header||connect to internal function|
The pinout of the extension connector X404 is described in table 3.32.
|1||+3.0V_VREF2_0||Output||Primary LTC6813-1 3.0V reference voltage 2|
|2||+3.0V_VREF2_1||Output||Secondary LTC6813-1 3.0V reference voltage 2|
|3||+5.0V_VREG_0||Output||Primary LTC6813-1 5.0V regulated voltage|
|4||+5.0V_VREG_1||Output||Secondary LTC6813-1 5.0V regulated voltage|
|5||PRIMARY-GPIO1-OPT||Input/Output||Primary LTC6813-1 GPIO1|
|6||SECONDARY-GPIO1-OPT||Input/Output||Secondary LTC6813-1 GPIO1|
|7||PRIMARY-GPIO2-OPT||Input/Output||Primary LTC6813-1 GPIO2|
|8||SECONDARY-GPIO2-OPT||Input/Output||Secondary LTC6813-1 GPIO2|
|9||PRIMARY-GPIO3-OPT||Input/Output||Primary LTC6813-1 GPIO3|
|10||SECONDARY-GPIO3-OPT||Input/Output||Secondary LTC6813-1 GPIO3|
|11||PRIMARY-GPIO4-OPT||Input/Output||Primary LTC6813-1 GPIO4|
|12||SECONDARY-GPIO4-OPT||Input/Output||Secondary LTC6813-1 GPIO4|
|13||PRIMARY-GPIO5-OPT||Input/Output||Primary LTC6813-1 GPIO5|
|14||SECONDARY-GPIO5-OPT||Input/Output||Secondary LTC6813-1 GPIO5|
|15||PRIMARY-WDT||Output||Primary LTC6813-1 watchdog output|
|16||SECONDARY-WDT||Output||Secondary LTC6813-1 watchdog output|
|17||PRIMARY-TEMP-ALERT||Output||Primary board temp. sensor alarm output|
|18||SECONDARY-TEMP-ALERT||Output||Secondary board temp. sensor alarm output|
The GPIO lines 6 to 9 are wired to the connector X405 permanently. There is no internal function for this GPIO lines. The pinout of the extension connector X405 is described in table 3.33.
|1||PRIMARY-GPIO6||Input/Output||Primary LTC6813-1 GPIO6|
|2||SECONDARY-GPIO6||Input/Output||Secondary LTC6813-1 GPIO6|
|3||PRIMARY-GPIO7||Input/Output||Primary LTC6813-1 GPIO7|
|4||SECONDARY-GPIO7||Input/Output||Secondary LTC6813-1 GPIO7|
|5||PRIMARY-GPIO8||Input/Output||Primary LTC6813-1 GPIO8|
|6||SECONDARY-GPIO8||Input/Output||Secondary LTC6813-1 GPIO8|
|7||PRIMARY-GPIO9||Input/Output||Primary LTC6813-1 GPIO9|
|8||SECONDARY-GPIO9||Input/Output||Secondary LTC6813-1 GPIO9|
126.96.36.199. External Isolated DC-Supply¶
It is possible to supply the BMS-Slave Board by an external DC power supply with a voltage range of 8V to 24V. The DC input is protected against reverse voltage and over-current (with a 1.25A fuse). The external DC supply has to be connected on connector X1001 or X1002 (both connectors are in parallel for daisy chaining the supply). The pinout of the connectors X1001 and X1002 is shown in table 3.34.
|1||DC+||Input||positive supply terminal|
|2||DC-||Input||negative supply terminal|