Integrated hot-swap and ideal diode controller for safety-critical applications
STMicroelectronics’ new STPM801 chip is the market’s first automotive-qualified integrated hot-swap and ideal-diode controller with a feature set designed for functional-safety applications.
The Ideal Diode Controller drives an external MOSFET as a replacement for the bulkhead diode normally used as input-side reverse polarity protection and to maintain output voltage. Since the voltage drop across the MOSFET is less than the forward voltage of a Schottky diode, the power dissipation is reduced during regular operation. For example, if a voltage with reversed polarity is applied to the input due to a power supply fault, a brownout event, or an input-side short circuit, the resulting negative current spikes are blocked by turning off the MOSFET.
The ideal diode controller circuit also provides an OR connection of the power supplies. For example, it is possible to switch between a main battery and an auxiliary battery to ensure an uninterrupted supply of power to safety-critical equipment such as autonomous driving systems or driver assistance systems.
The integrated hot-swap controller drives a second external N-channel MOSFET to protect connected loads during hot-swap events. A soft-start function controls the turn-on transient of this second MOSFET by charging a capacitor of known value connected to the gate of this MOSFET with constant current to inhibit high inrush currents. The over-voltage and under-voltage pins turn off the output voltage as soon as the input voltage leaves the specified range.
The device is also equipped with protection and monitoring features for applications that must meet functional safety requirements for systems up to ASIL-D (Automotive Safety Integrity Level) as defined by ISO 26262. All features are integrated into a 5 x 5 mm VFQFN-32 package, saving board space and minimizing the need for external components.
The STPM801 is rated for an operating voltage range of 4 V to 65 V and has a quiescent current consumption of 25 µA. It is resistant to the harsh electrical conditions of automotive applications and places minimal load on the battery of a parked vehicle. Applications for the device include zone and body ECUs, ADAS ECUs, high-performance computing ECUs, infotainment ECUs, redundant power systems and dual-battery systems.
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