Build Robust Automotive Batteries with Infineon’s BMS Chipsets
One of the major challenges in developing automotive BMS is maintaining the lifetime accuracy and robustness without blowing up the cost of the bill of material.
All electric vehicles are driven by lithium-ion (Li-ion) batteries. Despite the drastic cost drop in the Li-ion battery cells, the battery remains the most expensive part in an electric vehicle. As such, maximizing the battery performance and lifetime is a key objective for Mild-Hybrid, Plug-in-Hybrid, Full-Hybrid and Battery-Electric Vehicles (xEV) to be sustainable. Such an objective is challenged by the complexities associated with Li-ion battery cells. To mention few, Li-ion chemistries are known for their extremely flat State of Charge (SoC) curve and sensitivity to environmental (e.g. temperature) and aging elements (e.g. number of charging cycles). Additionally, operating the Li-ion cell outside its safe operating area can drastically reduce its lifespan and even damage it. Thus risking the safety of the passengers.
To overcome the challenges mentioned above, a Battery Management Sytem (BMS) is required
The primary Functions of the BMS are:
- Monitoring of the battery cells’ conditions (e.g.: voltage, temperature, current, pressure, etc.)
- Calculation of all the battery states (e.g.: states of charge (SoC), health (SoH), power (SoP), safety (SoS), etc.)
- Protection of the battery by disconnecting it during critical events (e.g. over current event) or request the thermal managements intervention (e.g. cooling or heating the battery when needed)
- Optimization the performance of the battery (e.g. by feeding the charger with the optimal charging protocol to extend cell life)
Sense and Balance Cells Accurately with TLE9012DQU
Cell Monitoring and Balancing (CMB) is directly attached to the cells. Its key function is to monitor the cells’ temperature and voltage. The greatest challenges of the CMB lay in the following points:
- A CMB is attached to an “always on” system. Even when the battery cells are empty, they maintain more than 50% of their nominal voltage. Thus, a CMB is more prone to aging than most of other components in the car.
- A CMB is directly connected to a high voltage system. Thus isolating the CMB and protecting it from hotplug events is necessary.
- The CMB needs to maintain highest level of functional safety (ASIL-D). Any error in the measured voltages or temperature could result in missing on dangerous events such as thermal runaway.
To address these challenges, Infineon developed TLE9012DQU
The TLE9012DQU is a 12-channel CMB device supporting ASIL-D systems featuring:
- One ADC per channel with integrated digital filtering. These ADCs operate with a very high sampling frequency, thus allowing the use of smaller capacitance values and sizes. The measurement quality is not affected by these high frequencies, as the external filter is only required to avoid aliasing effects in the higher frequency bands and not used to filter noise from other parts of the vehicle, which is achieved via the digital filter.
- No requirement for external TVS diodes to protect it from hot plug events. This eliminates any EoL aging effects they would cause.
- A proprietary integrated stress sensor that compensates for mechanical stresses, thus automatically recalibrating the ADCs from any drifts. The stress sensor can therefore compensate board level stress reflecting back on the chip.
- To measure the temperature of the cells, negative temperature coefficient (NTC) sensors are directly connected to TLE9012DQU. No external components are required as internal current sources can power the NTC. This reduces thermal measurement drifts and makes its thermal measurement accuracy best in class.
- Stable current consumption throughout the whole operating range, with minimal variance from device to device to avoid introducing additional imbalances between cells.
- High absolute cell voltage measurement accuracy including all errors over the device lifetime of ±2.1 mV (End-of-Life @3.6 V and 25ºC).
- Less than ±1.0 mV relative accuracy over all devices against each other at any given point in the device lifetime (under similar conditions), for superior relative accuracies within one battery pack.
- Proven hot plug robustness (no single additional external component needed) tested in cooperation with customers around the world using worst case assumptions.
- Proven BCI robustness (with no ADC or communication interference at all) under harshest conditions (200 mA injected in sensing and daisy chain wires). All purely capacitive coupled (no choke needed) with a cost-effective 1 nF capacitor.
- Proven board-level ESD robustness supporting 8kV gun testing without any additional external components.
- Parallel ADC structure combined with high ADC sampling (14 MHz) and super large OSR (up to 131072) for stable voltage readings even under heavy noise without any large external RC filter.
Measure the Current Accurately and Fast with PSoC™ HV PA Shunt IC and TLE4972 Coreless Hall Sensor
The pack monitoring unit sits in the junction box and is responsible for monitoring the packs current values, isolation and disconnection. The current measurement is needed for:
- Accurately calculating the state of charge with Coulomb counting. Every error in state of charge is a loss in battery capacity which means loss in car mileage.
- Over Current Detection (OCD) due to e.g. short circuits or isolation failure. The earlier an over current is prevented, the less the automobile manufacturer (OEM) needs to upsize the wirings of the DC bus.
To accurately calculate the state of charge and fast over current detection an accurate current sensor is required. Infineon has developed PSoC™ HV PA, and TLE4972 to address these challenges.
For high precision sensing, Infineon has developed the PSoC™ HV PA which features:
- Shunt-based current measurement with up to 0.3% accuracy
- Dual shunt sensor support for redundant measurements
- Unique dual ADC (two precision sigma-delta ADCs with 16-20+ bits) and four digital processing channels (two including FIR filters) to provide effective four channels analog front-end (as shown in the figure below)
- Automatic gain control enabling measurement of large starting currents or small battery-off currents accurately
- Pack voltage monitoring using external voltage divider with up to 0.15% accuracy
- Additional channels for temperature sensing with up to 1ºC accuracy
- Open shunt detection capability
- Arm® Cortex®-M0+ controller available for running system diagnostics, signature recognition and Coulomb count algorithms
- Additional analog inputs to monitor the relays
- Measurement range 0 to 31 mT (0 A to >1 kA) enabling large measurement range
- Fast over current detection output OCD
- Analog output
- High bandwidth (typ. 210 kHz) for fast measurement
- 3.3 V supply voltage
- High accuracy over temperature & lifetime
- Intrinsic stray-field robustness through differential measurement
- Automotive grade qualified
- ISO 26262 complaint development – Component rating: ASIL-B
Communicate with CMBs Robustly and Safely Redundant with TLE9015DQU iso UART Transceiver
All CMB measurements and actions need to be communicated to and from the main BMS controller. However, the different CMB units sit in different voltage islands. This means that isolated communication is required, to transmit information safely between the CMB and the main BMS controller. The challenge however when building the isolated communication lay in the following points:
- Robustness of the isolation: The battery pack operates under very electrically noisy conditions, so the stability and quality of the transmitted information can be drastically impacted by the isolation.
- Bandwidth and latency: Operating and measuring all CMBs synchronously is impacted by the bandwidth and latencies of the communication solution.
- Power consumption: Booting the system via the communication links, with no power consumption.
- Safety: Meeting the appropriate ASIL level and a fail operational state of the communication. Otherwise, if the communication with the AFEs breaks, the entire pack will need to be disconnected.
- Cost of isolation: There are many ways to isolate the communication, but the cost of isolating can become very expensive.
To address these challenges, Infineon developed TLE9015DQU
The TLE9015DQU is an isolated UART communication transceiver enabling the communication between the low voltage domains (e.g. master controller) and the high voltage domains (e.g. CMBs), featuring:
- Two UART ports for serial communication to host microcontroller
- Two iso UART ports for daisy chain communication inside battery pack
- Fully transparent communication scheme from µC to sensing IC (TLE9012DQU)
- Ring mode topology compatible (only 1 device needed)
- Supporting up to 2 Mbit/s
- High robustness against external noise
- General purpose error pin
- Two external fault inputs with internal latching
- Error output pin to trigger external microcontroller › Internal supply monitoring › AEC-Q100 qualified
Build High Performance Battery Control Unit (BCU) with AURIX™ MCUs
Li-ion battery is represented using complex mathematical models. Such models give a deeper insight into the state of the battery cells as well as the individual components surrounding them. Additionally, such models might be adapted over time, if the OEM discovers an improved version of the model. As such, a BCU is responsible for running all the battery algorithms, housekeeping and communicating with the domain controller. Such a BCU will mainly consist of a powerful microcontroller supporting ASIL-D qualification. For that purpose, Infineon developed AURIX™.
The new 40 nm µC generation TC3xx AURIX™ from Infineon Technologies ideally fulfills all requirements for the required processor of the BMS
AURIX™ TC3xx Family
- Scalable family concept with different FLASH sizes and package variants
- Offering of all ASIL-C-D relevant prerequisites (for example lockstep core, ECC in FLASH, SRAM as well as on the SRI crossbar) in order to be able to develop an ISO 26262 compliant E/E system in a certifiable manner
- ISO 26262 compliant and TÜV certified AURIX™ development by Infineon
- Special Safety SW driver SafeTcore with documentation (Safety Case, Safety Manual, FMEDA & Safety Concept)
- Further ISO 26262 supporting portfolio to keep the development effort at the customer’s site within manageable limits
- Leakage current monitoring to the chassis
- Main switch relay monitoring
- Main battery management
- Standby function for parking situations
- Battery thermal management
- Crypto algorithms for securing the original OEM battery
Achieve ASIL-D Safety Level BCU Easily with OPTIREG™ PMIC Family Products
The high voltage battery is a highly important component when it comes to safety. Any undetected errors by the BMS might lead to serious failure of the entire vehicle. Thus risking the safety of the passengers. As such, BCUs must be designed to meet ASIL-D safety level requirements. In addition to the AURIX™ features, the OPTIREG™ PMIC family enable easy realization of ASIL-D in the BCU.
For that, Infineon developed TLF35584QVVS1 and TLF35584QVVS2
- Efficiency and flexibility
- Enables ASIL-D on system level
- Easy ISO 26262 implementation by full documentation set
- Pre-/post-regulator concept: Boost and buck/LDOs and trackers for
- μC (main, ADC/reference, StBy)
- Transceivers
- Sensors
- Integration of functional safety (features supporting ASIL-D)
- UV/OV-monitoring
- Flexible watchdogs
- Error-monitoring
- Safe state controller with 2 outputs
- BIST
Detect Early Thermal Runaway with KP23x and KP25x Pressure Sensors
Thermal runaway is by far the worst thing that could happen to a Li-ion battery. It not only leads to the total damaging of the battery but also possesses a life-threatening hazard upon the passengers. As such an early and accurate thermal runaway detection is crucial.
Besides a cell temperature monitoring via the TLE9012DQU sensor inputs, Infineon developed a set of pressure sensors KP23x and KP25x which can be used to additionally monitor the pressure in the battery. This can ensures a more accurate and early thermal runaway detection.
The pressures sensors KP23x and KP25x are featuring:
- Compatible with the GTR20 regulation phase 1
- Reliably detect cell opening without a false alarm
- ISO 26262 Ready (for ASIL-B system) for KP25x
- Automotive qualification according to AECQ-100
- Multi interfaces: Analog (KP23x) and digital (KP25x) interfaces
- Application specific pressure range: Required battery pressure ranges from 60 to 165kPa
- High accuracy: High accuracy of ±1.0kPa over a large temperature range (-40..125°C)
- Robust: Robustness for placement into Battery pack or in BMS module
- Flexibility for thermal runaway detection with KP2xx:
- Delta pressure with the BAP sensors from ECU management board
- Delta pressure with the microcontroller AURIX™
System ASIL-D Safety Level
Development Boards
BMS Eval Board TLE9012QU
BMS Eval Board TLE9015QU
AURIX™ 2G TC397 Application Kit
With Infineon’s radar-specific evaluation board fitted with an AURIX™ TC397XA TFT, customers can connect through a dedicated Radar Interface MMIC and quickly start developing, evaluating and testing a full radar application.
The board features various communication interfaces such as CAN FD, Gigabit Ethernet, SPI FlexRay as well as an LCD XGA Display. It also gives access to all the digital and analog IOs available from the LFGBA-292 package of the microcontroller.
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