nxp UM11846 Battery Junction Box User Manual

nxp UM11846 Battery Junction Box

Document information

pack, contactor, shunt, accuracy, temperature, precharge resistor, chassis, DCLINK, CAN, CANFD, CAN-FD
Abstract| This user manual targets the RD772BJBCANFDEVB board. The RD772BJBCANFDEVB is a typical battery junction box (BJB) solution that can be used in high-voltage battery management systems (BMS). The RD772BJBCANFDEVB is part of the high-voltage BMS reference design offered by NXP.

Revision history

Important notice

For engineering development or evaluation purposes only

NXP provides the product under the following conditions:
This evaluation kit is for use of ENGINEERING DEVELOPMENT OR EVALUATION PURPOSES ONLY.
It is provided as a sample IC pre-soldered to a printed-circuit board to make it easier to access inputs, outputs and supply terminals. This evaluation board may be used with any development system or other source of I/O signals by connecting it to the host MCU computer board via off-the-shelf cables. This evaluation board is not a Reference Design and is not intended to represent a final design recommendation for any particular application. Final device in an application heavily depends on proper printed-circuit board layout and heat sinking design as well as attention to supply filtering, transient suppression, and I/O signal quality.

The product provided may not be complete in terms of required design, marketing, and or manufacturing related protective considerations, including product safety measures typically found in the end device incorporating the product. Due to the open construction of the product, it is the responsibility of the user to take all appropriate precautions for electric discharge. In order to minimize risks associated with the customers’ applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. For any safety concerns, contact NXP sales and technical support services.

WARNING: Lethal voltage and fire ignition hazard
The non-insulated high voltages that are present when operating this product, constitute a risk of electric shock, personal injury, death and/or ignition of fire. This product is intended for evaluation purposes only. It shall be operated in a designated test area by personnel qualified according to local requirements and labor laws to work with non-insulate d mains voltages and high-voltage circuits. This product shall never be operated unattended.

RD772BJBCANFDEVB

Introduction

The RD772BJBCANFDEVB is a BJB reference design for high-voltage battery management systems. The solution features high-voltage, current, and isolation-resistance measurements. The RD772BJBCANFDEVB has a communication port using CAN protocol.

Figure 2 shows a typical BJB with functions allocated to it and the context in a battery management system.

Kit contents/packing list

The kit includes

• Assembled and tested board in antistatic bag
• High-voltage measurement cables
• External thermistor connection cable
• Power supply and CAN communication cable

Getting to know the hardware

Board overview

• The RD772BJBCANFDEVB supports all typical functions of a BJB.
• The RD772BJBCANFDEVB is supplied either with an isolated DC-DC from low-voltage domain (12 V) or directly from the high-voltage battery with a self-supply circuitry.
• The RD772BJBCANFDEVB includes a galvanic isolation enabling communication between the high-voltage domain of the RD772BJBCANFDEVB and low-voltage domain of the controller.

Board features

Main features of the RD772BJBCANFDEVB:

• Five inputs high-voltage positive measurement up to 500 V
• Two inputs high-voltage negative measurement down to −500 V
• Single shunt for current measurement ±1500 A
• Shunt temperature measurement from −40 °C to +105 °C
• Connection to the precharge resistor for temperature measurement
• Passive isolation resistance measurement between high-voltage and low-voltage domains
• Two EEPROMs for data and calibration data storage
• Controller Area Network (CAN) line followed by an isolated gateway for communication with other systems
• Additional galvanically isolated electrical transport protocol link (ETPL) for communication with other systems

Block diagram

Figure 3 shows the main functions as well as the input and output of the battery junction box.
The voltage conditioning block is scaling down the high voltage from 0 V to 500 V to 0 V to 4.85 V range for analog-to-digital conversion by the MC33772C analog input. Sense control function enables the voltage divider. A general- purpose input/output

(GPIO) enables the switch in the voltage divider through a level shifter. This function prevents consumption of the voltage divider when the measurement is not performed
(see Section 6.1 for an example of the sense control).

The resistance measurement function enables a connection to the chassis of the vehicle. Then several measurements are performed with different parallel resistor configurations. The isolation resistance between high-voltage domain and low-voltage domain is further computed in the main controller based on the voltage measurement (see Section 5).

• The communication is based on a Controller Area Network (CAN) line. A MC33665 acts as a gateway and transfers the information to the MC33772C in TPL.
• An additional communication line is based on the TPL working up to 2 Mbit/s. It is an NXP isolated communication protocol.
• Two negative temperature coefficient resistors (NTCs) monitor the shunt temperature and the precharge resistor temperature. The analog inputs are configured as ratiometric analog inputs with reference to a voltage delivered by the MC33772C.
• The battery junction box is supplied by a 12 V (typ.) either from the high-voltage battery with a buck converter or from a 12 V battery from low-voltage (LV) domain through an isolated DC-DC (see Section 4.11 for details).
• The MC33772C performs analog-to-digital conversions of the sensed voltages and current, as well as battery coulomb counting.
• The shunt is a 100 μΩ resistor with ±1500 A capability measurement. The resulting shunt voltage is redundantly measured by the two MC33772C.

Board detailed features

The RD772BJBCANFDEVB embeds two MC33772C ICs. Table 1 and Table 2 show the measurement signal allocation per MC33772C:

Table 1. Battery junction box signal allocation to MC33772C AFE1

Table 2. Battery junction box signal allocation to MC33772C AFE2

The GPIO4, GPIO5, and GPIO6 from AFE1 and AFE2 are selecting the signals for measurement. Table 3 shows the control signal allocation per MC33772C:

Table 3. GPIO control table

Board description

Figure 4 shows the location of functions over the board:

Figure 5 shows the allocation of signals in different board connectors:

VCOM LED: The VCOM LED is on the board, as shown in Figure 5. The VCOM LED indicates when the device is in normal mode. Upon reset, the MC33772C enters into normal mode (VCOM turns on). If there is no activity on the bus after a timeout period of 60 s, the device enters low-power idle mode (VCOM turns off). Once the device is initialized, if no communication occurs on the TPL bus after 1 s, the device resets and the LED turns off (VCOM off). Depending on the device settings, the VCOM LED may flash with 8 s interval during cyclic acquisition.

Connectors

Figure 5 shows the location of connectors on the board. Table 4 to Table 8 list the pinouts for each connector.

Table 4. Precharge resistor temperature connector (J1)

Table 5. Negative signal connector (J2)

Table 6. High-voltage DCLINK(+) connector (J3)

Table 7. High-voltage charger connector (J4)

Table 8.  Shunt voltage connector (J5)

Table 9. Additional TPL line connector (J6)

Table 10. Additional TPL line connector (J7)

Table 11. Direct TPL line connector (J9)

Table 12.  Chassis connector (J11)

Temperature measurement: The RD772BJBCANFDEVB offers two temperature measurements: one temperature measurement of the shunt and one temperature measurement of the precharge resistor. The NTC used is B57232V5103F360. The voltage divider is supplied by VCOM from MC33772C.

Cell terminal voltage measurement: CT1 of each MC33772C is used for voltage measurement. The other CT pins are unused. To comply with the maximum differential rating between pins, the unused CTx and CBx pins are externally biased with a voltage divider. The resistor values for the CTx/CBx biasing have been calculated to comply with maximum ratings and to comply with the supply voltage range specified in Section 4.11.

Bus terminal communication: The 1:1 transformer galvanically isolates the superior control unit on LV domain to the MC33772C AFE1 on High-Voltage (HV) domain. The TPL bus has a direct connection between AFE1 and AFE2. Isolation is not required, as both devices share GND and supply. For additional information about the TPL protocol and external components, refer
to MC33772C data sheet[1].

Power supply: The battery junction box offers two options for the supply:

• 12 V from a DC-DC converter from low-voltage domain
• 12 V from the high-voltage domain with a step-down converter

Table 13. Power supply

Symbol| Parameter| Conditions| Min| Typ| Max| Unit
---|---|---|---|---|---|---
VCC| supply voltage| high-voltage domain| 9| 12| 13.5| V
ICC| supply current| normal mode; ADC active; TPL communication active; 12 V supplied without DC-DC| —| 21| —| mA
sleep mode| —| 430| —| µA
normal mode; ADC active; TPL communication active; 12 V supplied from DC-DC| —| 37| —| mA

The default supply is from the DC-DC converter. On RD772BJBCANFDEVB, an industrial integrated DC-DC converter is used. If the BJB is used in an automotive environment, an automotive-qualified, isolated DC-DC is recommended. Four resistors connect or disconnect the power supply options. Table 14 details the resistor connections for the supply selection source.

Table 14. Power supply selection

Isolation measurement

The BJB features a passive isolation resistance measurement circuit. A dedicated circuitry connects the chassis to specific resistor networks. This connection unbalances the network as a function of the resistance between the chassis and the battery. Figure 6 shows the resistor networks and chassis connections.

The ISO_Q1, ISO_QL1, and ISO_QL2 prevent continuous current leakage between the battery rails. ISO_Opto connects or disconnects the chassis to the isolation resistance measurement circuit. The principle of operation is to close ISO_Q1 then to measure Vsense. This measurement is called V1. Then, ISO_QL1 closes and Vsense is measured again. This second measurement is called V2. After the second measurement, the two voltages, V1 and V2, are used in the formulas Equation 1 and Equation 2, assumed to be implemented in the battery management unit (BMU), to compute Riso+ and Riso–. To ease the computation, the Y1 to Y4 conductances of the R1 to R4 resistances are considered. Vbat is the battery voltage. The last low branch, that includes R5 and is enabled by ISO_QL2, is a redundant branch of the one enabled by ISO_QL1. This last branch can be used instead of ISO_QL1 one or to make a third measurement.

High-voltage measurement: The high-voltage nodes are sensed through a voltage divider to scale the voltage down to a range suitable for the input of the MC33772C. Figure 7 represents the DCLINK(+) and DCLINK(−) measurements. The capacitor represents the total traction inverter load capacitance. A reference is in the negative measurement path to allow negative voltage measurement.

Sense voltages are computed in the BMU with Equation 3 and Equation 4:

Blanking time: Before doing any measurement with the MC33772C, a blanking time is required to secure that the voltage is stabilized before the analog- to-digital conversion. Figure 8 shows the complete path from GPIO output enable to ANx input. Figure 9 shows the time needed before measurement. This blanking time is 2 ms minimum.

Low-voltage input signals emulation: All high-voltage nodes are sensed with a voltage divider to lower the voltage in a range suitable for the MC33772C analog input (4.85 V max). If the solution must be tested with lower voltage (5 V, 12 V, or 15 V), the voltage divider ratio has to be adapted. In Figure 10, the resistor has been chosen for 3.75 V at MC33772C inputs.

Current measurement

Current sense input selection

The battery junction box board allows the customer to apply an external voltage to simulate the current across the shunt. The maximum differential voltage is ±150 mV at MC33772C current sense inputs.
Figure 11 shows the resistor configuration for shunt usage and Figure 12 shows the configuration for external voltage usage.

Layout note

The layout of the current sense has been designed to connect an external voltage source to simulate the battery current. The connection to the shunt is not redundant, as it should be. Figure 13 shows the layout on the BJB reference board and Figure 14 shows the layout to be implemented on the final application to secure the redundant connection to the shunt.

Battery junction box filters

A low-pass filter is implemented on each measurement input. Table 15 summarizes the cutoff frequencies of all input signals.

Table 15. Cutoff frequencies

Note: The safety mechanism SM05 (OT/UT diagnostic on ANx) shall not be used with the capacitor computed for above cutoff frequencies. If SM05 is used, then the capacitor shall be below 10 nF. This limitation applies to pins set as analog inputs. For SM05 safety mechanism details, refer to the MC33772C safety manual.

Communication

By default, the reference design communicates with the Battery Management Unit (BMU) with a Controller Area Network protocol (CAN), as detailed in Figure 15 .

CAN communication

• The CAN lines coming from the BMU are connected to J12. The TJA1443 acts as a transceiver and interfaces the CAN lines with the MC33665. The MC33665 is a gateway that can be configured to forward all the messages between the BMU (CAN) and the MC33772 (TPL).
• The user must put jumpers on J13, J14 and J15 to communicate in CAN with the RD772BJBCANFDEVB.
• The jumper J16 keeps the MC33665 awake. This feature is useful when using a software tool with a delay between messages longer than the MC33665 timeout. If the MC33665 sleep feature is necessary, the jumper can be removed.

TPL communication

• The RD772BJBCANFDEVB can be converted to a TPL Battery Junction Box by removing J14, J14, and J15. Then, the TPL line connected to J9 bypasses the MC33665 and is connected to the MC33772.
• Two additional TPL lines are available on J6 and J9. These lines are directly connected to the MC33665 and could be used to interface the RD772BJBCANFDEVB with other TPL boards. The
• MC33665 could then distribute the messages from the BMU to any TPL line.

Available accessories

Table 16. Bill of materials

References

• Data sheet MC33772C http://www.nxp.com/MC33772C

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References

• MC33772C | 6-Channel Li-Ion Battery Cell Controller IC | NXP Semiconductors

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