Melexis boosts accuracy of Hall-effect DC current sensing

This digital solution brings 0.5% accuracy at an affordable price in a compact design. It integrates IVT measurement capability, embeds a microcontroller (MCU) to offload processing from the ECU, and benefits from pre-installed safety features. The MLX91230 is perfect for EV battery management and power distribution systems.

An alternative to existing technology

One recurring problem within the design of EVs is designers being reliant on shunt technology for its simplicity but struggling to make the thermal budget work. As current passing through the sensor increases, the resistance needs to go down to maintain the same thermal losses (due to the system imbalance). Similarly, designers using fluxgate technology to benefit from its galvanic isolation and high accuracy are failing to meet cost targets, as well as consuming too much power and space within the vehicle. It is these two prominent issues that have driven Melexis to develop the MLX91230.

In terms of applications, the sensor is designed to suit a wide variety of usages. For OEMs and Tier 1 looking to reduce production costs by in-sourcing DC current sensing design, this digital device provides an accurate and reliable monitoring solution while also meeting the highest functional safety requirements. For battery installations, it supports state of charge (SoC), battery state of health (SoH) and state of function (SoF) in both low voltage and high voltage systems. Ideal for battery management systems (BMS), battery disconnect units (BDUs), and battery junction boxes (BJB) deployments.

The MLX91230 offers manufacturers of products such as power distribution components, contactors, and relays with a safe and simple method of increasing their system’s capabilities through the addition of smart functionality, provided by the programmable flash microcontroller. Other innovative implementations include smart Pyro-Fuses, where the MLX91230 can be used to deploy local decision making, and in home energy storage systems such as solar power battery banks.

MLX91230 accuracy and embedded MCU

Thanks to the digital infrastructure and advanced signal processing, the MLX91230 is able to deliver an unprecedented 1% accuracy over temperature and over lifetime. While this achievement has been claimed by competing sensors before, the MLX91230 guarantees this accuracy not only for thermal drift but also lifetime drift and linearity errors. This represents an incredible improvement versus existing solutions.

The MCU with on-board flash memory supports custom software deployment and extensive compensation of system imperfections. Examples are ferromagnetic saturation onset, non-linearities, and hysteresis compensation. The MCU also supports frame customisation.

The MLX91230 is AEC-Q100 and ASIL compliant. It supports system integration up to ASIL D as per ISO 26262 functional safety requirements. The digital architecture and flexible MCU allow for simple integration into a range of battery-related and DC voltage/current applications.

Extensive functionality

The increase of electric vehicles and advanced driver-assistance systems (ADAS) places greater pressure on vehicle electronic design, whether this is to fulfil the latest functional safety requirements or to meet design efficiency or cost targets. The MLX91230 features an unrivalled set of benefits designed to meet the latest automotive demands:

• Hall-effect based DC current sensing – Provides galvanic isolation from the current measurement. 0.5% accuracy over temperature (–40℃ to 125℃) for a 1% lifetime drift all-in.
• IVT capability – Measures three physical quantities: current, voltage, and temperature .
• Flexible supply voltage – 5V (+/-10%) or 12V board net connection (LV124 compliant).
• Diagnosable on-chip overcurrent detection (OCD) – Allows direct input to the Pyro-Fuse driver.
• Functional Safety (SEooC) compliance – Removing the burden of developing all the safety mechanisms for the designer.
• Digital MCU with programmable flash memory – Enabling advanced compensations, message customisation, and development of intelligent systems.
• Additional voltage channel – Allows measurement with internal (12V/24V/48V) divider or external divider (high voltage or plausibility input). Facilitating battery resistance measurements, voltage safety/plausibility check, or additional signal input.
• On-chip junction temperature measurement – Provides insight into local temperatures.
• Selectable LIN or UART output – Enabling integration with 12V battery applications and power distribution modules, as well as direct communication with BMS or UART-over-CAN for across wire harness communication.
• Compact IC design – 8-pin SOIC package.

Summary

Until now, hall-effect sensors have been unsuitable for many high voltage designs. Thanks to the MLX91230, this cost-effective and contactless technology is not only a viable option, but in many cases it is now preferable to fluxgate and shunt sensors. For low voltage implementations, it is a similar picture. The aforementioned factors, combined with its simple integration, functional safety compliance, and advanced smart features enabled by the digital MCU, make the MLX91230 an obvious choice for designers.

“Melexis’ third generation of current sensors for the battery platform represents the very latest developments in our extensive automotive and sensor knowledge. With this portfolio we defined three key pillars, a dependable digital core, high accuracy, and functional safety compliance,” said Bruno Boury, Product Line Manager Current Sensors at Melexis. “The MLX91230 displays how our technology can meet new industry requirements and delivers unparalleled accuracy. All while remaining both cost-effective and easy to integrate within a wide variety of applications.”