Start designing with open load detection and limp home function. Leverage this tech note to enhance your body control module (BCM), while designing safe and reliable automotive systems.
Open Load Detection is a crucial and important function of the BCM. By using this function, the body control module can perform open-circuit diagnosis on loads, such as lamps and wiper motors, when the car is running or stopped. Open load diagnosis is an important function of the high-side switch (HSS). This function is mainly realized by measuring the current flowing through the power switch. Usually, the HSS has an inherent function of load current diagnosis. Open load diagnosis can be performed when the load is enabled or disabled. It is conducive not only to safe driving but also to maintenance and repair.
Power switches from different manufacturers in the market also have this function. However, with the popularity of LED lamps, OEMs require a lamp driver to be compatible with both the high-current diagnosis of lamp bulbs and the low-current diagnosis of LED lamps. Conventional high-side switches in the market are difficult to be compatible with the two. Most HSSs cannot detect current accurately below 300 mA. The solution introduced here can detect not only the large current of conventional bulbs, such as a current greater than 10 A, but also the small current of LED lamps, such as a current greater than 5 mA.