2. Master-Unit

This section describes the hardware modules used in foxBMS. Fig. 2.9 shows a block diagram of the foxBMS Master Unit with all its components.


Fig. 2.9 foxBMS Master Unit hardware block diagram

2.1. Supply 0 (primary)


Fig. 2.10 Supply for all circuit parts related to the primary part of foxBMS

The external supply for the BMS-Master Board is divided in a part supplying the interlock circuit, the contactors (SUPPLY_EXT2), and the rest of the circuit (SUPPLY_EXT0) as shown in Fig. 2.10 . The foxBMS Master Unit can be supplied with a voltage between 12V and 24V DC. The primary part of the foxBMS is isolated from SUPPLY_EXT0 by an isolating DC/DC converter (IC202). The 5V output of the DC/DC converter is stepped down to 3.3V by an LM1085 LDO (IC201). The output of IC201 (+3.3V_0) supplies the primary microcontroller MCU0 and the related circuits.

2.2. Supply 1 (secondary)


Fig. 2.11 Supply for all circuit parts related to the secondary part of foxBMS

The secondary part of foxBMS is also supplied by SUPPLY_EXT0 as shown in Fig. 2.11. Also the secondary part of the BMS-Master Board is isolated from SUPPLY_EXT0 by an isolating DC/DC converter (IC302). The 5V output of the DC/DC converter is stepped down to 3.3V by an LM1085 LDO (IC301). The output of IC301 (+3.3V_1) supplies the secondary microcontroller MCU1 and the related circuits.

2.3. MCU0 (primary)


Fig. 2.12 Boot and reset circuit for the primary microcontroller

Fig. 2.12 shows the boot and reset related circuits of the primary microcontroller MCU0. MCU0 can be manually reset by push button S401. Please note that the housing has to be opened to reach S401, therefore resetting MCU0 by means of S401 is intended for use in a laboratory setting/debugging situation.


Fig. 2.13 ADC reference voltage for the primary microcontroller

The ADCs of the primary microcontroller MCU0 are supplied with a 2.5V reference voltage provided by an ADR3425 (IC401) as shown in Fig. 2.13.


Fig. 2.14 Clock circuits of the primary microcontroller

The primary microcontroller MCU0 is clocked by an 8MHz oscillator as shown in Fig. 2.14. An separate oscillator (Q402) is used to clock the RTC (real time clock) integrated in MCU0.

2.4. Interface between MCU0 and MCU1


Fig. 2.15 Interface between primary and secondary microcontroller

Besides being linked over the common interlock line, the primary and secondary microcontroller also have a common SPI data interface. The secondary microcontroller MCU1 acts as the master in the SPI communication. The interface is isolated using an ADUM3401 as shown in Fig. 2.15.

2.5. Interface to Bender ISOMETER


Fig. 2.16 Interface to the Bender ISOMETER

The BMS-Master Board supports Bender ISOMETER IR155-3203/-3204/-3210. Two inputs are provided: one for a PWM coded diagnostic signal and one for a simple status signal (OK or NOK) as shown in Fig. 2.16. The Bender ISOMETER is supplied SUPPLY_EXT0 and may be switched on or off (lowside) by the BMS-Master Board. The input signals are limited to level of 5V with Zener diodes D701 and D702. In order adapt the interface for use with a IR155-3204/-3203 device, the solder jumper R705 has to be removed. The input signals are isolated from the microcontoller by an ADUM3301 (IC702).

2.6. CAN0


Fig. 2.17 Circuit of the CAN interface (CAN0)

The CAN0 interface is intended to connect additional sensors, such as the Isabellenhütte IVT-MOD-300 current sensor to the foxBMS Master Unit and the foxBMS Master Unit to other devices such as a test bench control unit or an HMI unit. The circuit in Fig. 2.17 shown the input circuit consisting of protection diode D801, common mode choke L801, C804, and termination resistors R801 and R802. The CAN transceiver TJA1052 provides isolation and can be put to sleep by the primary microcontroller MCU0 via an CPC1008N optocoupler (IC803). The external part of the CAN0 interface is supplied by SUPPLY_EXT0.

2.7. Interlock


Fig. 2.18 Interlock circuit

The primary and secondary microcontroller share a common interlock line as shown in Fig. 2.18. The interlock line is isolated from both microcontrollers MCU0 and MCU1 by optocouplers. The interlock line is supplied with 10mA by a current source (LM317 - IC901). It can be interrupted by the primary microcontroller MCU0 via optocoupler IC902 and can be read back by MCU0 via optocoupler IC903. The secondary microcontroller MCU1 can interrupt the interlock line via IC904 and read the interlock status via IC905. The 10mA cause a voltage drop on R906, which turns on MOSFET T901. T901 switches the common ground of all contactors (connected to the BMS-Master Board and BMS-Extension Board). Therefore, when the interlock line is interrupted, the contactors are no longer supplied and open.

2.8. Contactors


Fig. 2.19 Contactor circuit, exemplarily shown for contactor0

The foxBMS Master Unit can control up to 9 contactors: 6 on the BMS-Master Board and 3 on the BMS-Extension Board. The according control and feedback circuit is exemplarily shown for contactor 0 in Fig. 2.19. The contactor is switched on and off by an AQV25G2S photoMOS (IC1001) by the primary microcontroller MCU0. Every contactor channel is protected with slow blowing fuse (F1001) type Schurter UMT-250 630mA (3403.0164.xx). The free wheeling diode D1001 is not populated. It has to be inserted when contactors are used, that do not provide an internal free wheeling diode. The contactor interface also supports a feedback functionality for contactors with auxiliary contacts. The contactor status can be read back by MCU0 via an ADUM3300 (IC1103).

2.9. Isolated USB interface (primary and secondary)


Fig. 2.20 USB interface circuit

Both mircocontrollers MCU0 and MCU1 provide an isolated USB interface, as exemplarily shown for MCU0 in Fig. 2.20. A FT231XS-R interface IC (IC1402) converts the USB signal to UART, which can easily be interfaced by the microcontroller. The UART signals are isolated by an ADUM3401 isolation IC (IC1403). The USB interface can be used to flash the microcontroller and for communication.

2.10. EEPROM


Fig. 2.21 EEPROM, exemplarily shown for the MCU0

The BMS-Master Board provides an 2MB EEPROM for data storage for the primary and secondary MCU (see Fig. 2.21). It uses an SPI interface, which is shared with the memory card, which is also connected to MCU0.

2.11. Isolated RS485 Interface


Fig. 2.22 Isolated RS485 interface circuit

On the BMS-Extension Board an isolated RS485 interface is provided. It can be used to communicate with the foxBMS Master Unit as an alternative to the CAN interface or the UART over USB interface. Moreover, via this interface, monitoring circuits (slaves) using RS485 instead of CAN or another proprietary communication protocol can be connected to the foxBMS Master Unit. Fig. 2.22 shows the RS485 interface schematic. The external part of the circuit is supplied via a voltage applied to pins 5 (7V - 20V) and 6 (GND) of connector X1301. The external supply voltage is also available on pin 1 (GND) and pin 4. IC1301 provides 5V supply voltage for the transceiver (IC1302) and the external side of the isolator (IC1303). The transceiver (LT1785) features a receiver enable (!RE) and a driver enable (DE) functionality, which can be controlled by the primary microcontroller via the signals RS485_MCU0_NRE and RS485_MCU0_DE respectively. For data transmission the signals RS485_MCU0_TX and RS485_MCU0_RX are used. The data signals are available on connector X1301 pins 1 and 2. The data signals and the enable signals are galvanically isolated from the BMS-Master Board by an ADUM3401 isolator IC.

2.12. Isolated Normally Open Contacts (isoNOC)


Fig. 2.23 Isolated normally open contacts (ISONOC0 examplarily)

The BMS-Extension Board provides 6 normally open contacts (ISONOC0 to ISONOC5) for multi-purpose use. Their function is exemplarily described for ISONOC channel0 ( shown in Fig. 2.23). Isolation and switching functionality are realized by AQV25G2S photoMOS (IC2001). The photoMOS are controlled by a MOSFET (T2001), which again is switched by the primary microcontroller (ISONOC0_CONTROL). The photoMOS is configured for a maximum load current of 6A at 50V. Diode D1002 is optionally and not populated by default. Both power terminals of the photoMOS are available on connector X2001 as ISONOC0_POSITIVE and ISONOC0_POSITIVE on consecutive pins 1 and 2.

2.13. Analog Inputs


Fig. 2.24 Non isolated analog inputs (analog channel 0 exemplarily)

For the acquisition of analog data, there are 5 ADC channels (ANALOG_IN_CH0 - ANALOG_IN_CH4) available on BMS-Extension Board board. Fig. 2.24 shows the input circuit for channel 0. The analog input of the microcontroller (ADC_MCU0_CH0) is protected by diode D1701, which clamps the input voltage to 3.3V. By default R1701 is shorted with jumper, while R1702 is 7.75kOhm and C1701 is 100nF. The analog input channels are available on connector X1701. A reference voltage of 2.5V is provided by IC1701 (ADR3425), which can supply a total load current up to +10mA and sink up −3mA. The reference voltage is available in X1701 next to every analog input pin. Pin 11 and 12 are connected to GND.


The analog inputs are not isolated. They are referenced to the same potential as the primary microcontroller.

2.14. Isolated GPIO


Fig. 2.25 Isolated GPIOs (Input 0 and 1; Output 0 and 1 shown exemplarily)

The BMS-Extension Board provides 4 isolated inputs and 4 isolated outputs for general purpose (shown in Fig. 2.25 ). Two ADUM3402 (IC1902 and IC1903) are used for isolation. Their external side of is supplied by SUPPLX_EXT0 via a 78L05F linear voltage regulator (IC1901). The inputs are equipped with a 10kOhm pull down resistor. All isolated GPIOs are available on the connector X1901 pins 1 to 8. Pins 9 and 10 of X1901 are connected to GND_EXT0.

2.15. Memory Card


Fig. 2.26 Memory card

On the BMS-Extension Board also a memory card slot can be found. It is directly connected to the Data Storage SPI of the primary microcontroller. Fig. 2.26 shows the schematic. Via the signal CARD_SUPPLY_CONTROL (primary microcontroller) the supply voltage of the memory card can be switched on and off.