Smart battery sensor computes battery status

February 28, 2011 // By Christoph Hammerschmidt
Freescale Semiconductor's MM912J637 battery sensor measures current, voltage and temperature of lead-acid batteries and deduces the status of the battery from these parameters. Amidst increasing numbers of hybrid electric vehicles and start-stop systems (“mild hybrid”), it becomes increasingly important for car designers to determine the battery status.

The MM912J637 combines an S12 microcontroller with an integrated analog control circuit in smartmos technology, significantly reducing the PCB footprint for the application. According to Freescale, the MM912J637 is fully AEC-Q100 compliant and qualified for operating temperatures from -40 through +125 degrees Celsius.

The device communicates with ECUs through a LIN interface. It contains a 16-bit Delta-Sigma ADC with two channels for concurrent measurement of current and voltage. In addition it contains a third ADC for temperature measurements. Current is measured across a shunt resistor at the negative pole while voltage is measured at the positive pole of the battery. Currents up to 2000 A can be measured at an accuracy of 5 mA.

Samples of the device are available now, with volume production scheduled to ramp up in September 2011. Evaluation kits as well as software tools are also available.

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