Electronica: ASIL D vehicle battery safety monitor and pyrotechnic trigger

NXP is aiming at ASIL D safety approval with a vehicle battery junction box controller IC, intended to fire the pyrotechnic disconnect switch during a serious fault, as well as report faults over a serial bus.

MC33777A, as it will be known, redundantly measures currents, voltages and temperatures, then deduces situations – a short circuit or a crash, for example – without the need for a microcontroller.

“It detects and reacts to a matrix of configurable events without waiting for specific current thresholds to be exceeded,” according to the company.

The pyro triggers are AK-LV 16 (2012-07) compliant and can deliver 1.2A 2ms or 1.75A 500μs pulses.

To increase reliability, the IC has two separate signal chains, both reading the same voltages and currents, and both capable of firing the pyrotechnic.

One of the two signal chains

Each of the channels has two main analogue inputs, one devoted to current measurement and the other available for voltage or current measurement.

Each of these measurement channels as two ADCs connected in parallel – one fast (16bit, 125kHz) and the other high-resolution (27bit 1kHz) – this makes four ADCs/chain and therefore eight on the chip.

Shunt temperature drift compensation is available (external temperature sensor required), as is Coulomb counting, over-current detection (threshold, di/dt calculation and melting fuse emulation) and support for 400V or 800V batteries.

Each signal chain also has eight GPIOs – so 16 in total on the chip – and each block of eight has its own multiplexed auxiliary ADC (16bit 1kHz) taking the device’s total ADC count up to 10.

There are two decision-making event managers, one per signal chain, which each take in data from the five ADCs and eight GPIOs and, alongside pyro-triggering and other features mentioned above, can do things like wake an external MCU or de-bounce an input.

The two signal chains share a single serial communication link to the outside world – a TPL3 isolated daisy-chain serial bus in one version of the chip, and an SPI bus in the second version.

Packaging is thermally-enhanced LQFP64 and operation is over -40 to 125°C.

There is a lot more going on in these ICs, and the associated data brief is well worth a look (the full data sheet is not public at the time of writing).

Applications are also foreseen with industrial batteries.

Find the MC33777A product page here, or at its official launch during Electronica 2024.

These are super-set devices. Cousins with similar part numbers are planned that do not include the voltage channel ADCs, some of which also only have one pyro-trigger output, or no pyro output.