Diodes Incorporated has announced two new ideal diode controllers with a wide input voltage range, low quiescent current, and overvoltage lockout protection.
Diodes Incorporated recently announced the AP74502Q and AP74502HQ ideal diode controllers targeted at 48 V applications. 48 V systems in vehicles are used to power subsystems that demand more power than 12 V rails can efficiently handle. These applications may include electric turbochargers, electric power steering, active suspension, and start-stop functionality.
The 80 V ideal diode controllers may simplify reverse battery polarity and overvoltage protection in vehicle architectures.
By running these loads on a separate 48 V rail, automakers can improve efficiency, reduce current, decrease wiring size, and support mild hybrid operation. However, with the increased voltage comes the increased risk of severe voltage transients and reverse current spikes, necessitating the use of diodes (or diode controllers) to protect circuitry in the system.
Ideal Diode Controllers for Any Rail
Both the AP74502Q and AP74502HQ (datasheet linked) come in an 8-pin SOT-28 package, which is AEC-Q100 qualified for automotive systems with a wide input range from 3.2 V to 75 V. In automotive systems, the input voltage can vary wildly due to temperature fluctuations (during a cold start crank, for example). The controllers can be used as both surge stoppers (over-voltage protection) and reverse polarity protection.
Key application configurations of AP74502 diode controllers.
Unlike traditional diodes, which drop some voltage and dissipate power as heat, the AP74502Q and AP74502HQ minimize voltage drop by driving an external N-channel MOSFET. When enabled, the controller drives the gate fully on, allowing current to pass with only millivolts of drop—significantly improving efficiency in high-current paths.
In reverse polarity conditions, the controller keeps the gate low, turning the MOSFET off and cleanly isolating the load. This approach offers the same protective behavior as a diode but without the power and thermal penalties, making it well-suited for 48 V automotive rail protection.
Leveraging a Charge Pump and OVLO Pin
The controllers use a charge pump that generates a voltage slightly higher than the input voltage to properly drive the gate of an external N-channel MOSFET. A charge pump is a type of DC-DC converter that uses capacitors to generate a voltage higher than the supply rail. It works by rapidly switching capacitors between different nodes to "stack" voltage levels, effectively boosting the available gate drive voltage. In this case, the charge pump allows the controller to drive the MOSFET gate above V_IN, which is necessary to fully turn on an N-channel MOSFET in a high-side configuration.
Surge-stopping capability of AP74502 diodes above cutoff voltage.
Importantly, the controllers also have an OVLO pin to set an overvoltage lockout value using a resistor divider. This switches off the gate drive when an overvoltage condition is detected.
The main difference between the AP74502H and AP74502HQ is that the latter has an 11 mA peak input gate drive current, while the H has a much lower peak input gate drive current of 60 µA. The increased peak input gate drive current enables faster switching of the external MOSFET.
Diode Controllers Purpose-Built for Automotive Applications
The diode controllers' features make them useful across a variety of automotive applications.
In ADAS and infotainment systems, where modules are sensitive to voltage fluctuations and need consistent uptime, reverse polarity and overvoltage protection help prevent damage during load dumps or service events. In body control modules and exterior lighting, where reliability and thermal efficiency are critical, the low voltage drop across the external MOSFET reduces heat buildup and improves system longevity. For USB charging ports, the ability to quickly disconnect the load during fault conditions protects both the power source and connected devices. The low standby current is a key advantage in systems that remain powered during engine-off states.
Combined, these features support robust, efficient power delivery in both legacy 12 V and emerging 48 V zones across the vehicle.
All images used courtesy of Diodes Incorporated.
