NXP Semiconductor has released the MC33777 battery junction box controller chip designed to monitor and protect battery systems in EV and hybrid-EV (HEV) vehicles.
The MC33777.
Compliant with ASIL-D requirements, the new IC redundantly measures battery pack currents, voltages, and temperatures. It also uses onboard diagnostics to initiate protective actions when it detects fault conditions. Its high level of integration eliminates the need for separate discrete components, external actuators, and processors, saving design time, board space, and cost. The MC33777 includes fuse emulation capabilities, replacing the use of expense single-burn fuses and improving the safety and reliability of EVs.
The MC33777 (datasheet linked) is available in a thermally enhanced LQFP64-EP package and is AEC-Q100 qualified with an operating temperature range of -40°C to 125°C.
Fuse Emulation Safeguards Against EV Fires
The MC33777’s fuse emulation technology eliminates the need for single-use, melting fuses traditionally used to isolate an EV’s high-voltage battery bus during a system fault. Melting fuses can be expensive and unreliable, making NXP’s fuse emulation technology a cost-saving opportunity for OEMs.
MC33777 block diagram.
The MC33777 uses internal logic based on measured current levels to simulate the behavior of a traditional melting fuse. When it reaches a protective threshold, integrated pyro switch controllers can independently drive up to two external pyrotechnic switches (redundant per ASIL-D requirements). The fast-acting switches use a small precision explosive force to physically disconnect the high-voltage battery from the vehicle drivetrain and other loads during fault conditions to ensure the safety of the vehicle and driver.
In total, NXP asserts that the MC33777’s unprecedented level of integration reduces the component count of battery junction box monitoring applications by as much as 80%, reducing PCB size requirements and lowering overall system costs.
Fast and Precise Sensing Channels
To meet ASIL-D requirements for automotive safety, NXP’s new chip makes current and voltage measurements through both precision and fast ADC channels. With 27 bits, the precision ADC channel can measure signals up to 1 kHz, while the fast ADC has 16 bits of resolution up to a signal bandwidth of 125 kHz. The device supports Hall sensor measurements as well.
Precision and fast current and voltage measurement.
These data acquisition capabilities allow the MC33777 to continuously measure battery current and slope every 8 µs to rapidly detect overcurrent conditions. According to NXP, the MC33777 can detect and act on configurable events up to ten times faster than traditional solutions.
The configurable logic capabilities of the MC33777 allow it to detect fault conditions (threshold, di/dt calculation, melting fuse emulation) and execute protective actions (pyrotechnic switch controller, MCU wake-up, GPIOs) without an external MCU.
Better EV Safety and Performance
Thermal runaway occurs when an EV battery cell short circuits and begins to heat up in an uncontrollable manner. NXP’s fuse emulation technology in the MC33777 safeguards against EV battery fires that burn dangerously hot and are difficult to extinguish. In an accident involving EVs, the speed and reliability of pyrotechnic switches can add an extra layer of safety. They can quickly disconnect high-voltage batteries from loads to avoid short circuits or overload conditions that might ignite an EV battery cell’s highly flammable liquid electrolyte.
The MC33777’s precise measurements are not just about safety but also performance. With more accurate voltage, current, and temperature measurements, EVs can operate longer from each charge and extend the time between charges.
All images used courtesy of NXP.
