Diodes Inc.
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Asynchronous Buck Converters Enhance Efficiency in Automotive 48-V POL Apps

Sept. 8, 2025
Diodes Inc.’s new buck converters operate across the complete automotive battery voltage range.

Citing high efficiency as the primary characteristic, Diodes Inc. announced the release of four new automotive-compliant asynchronous buck converters designed for 48-V low-voltage rail point-of-load (POL) applications

The AP68255Q/AP68355Q and AP6A255Q/AP6A355Q incorporate 500-mΩ power MOSFETs to deliver up to 3.5 A of continuous output current. The converters cover the full automotive battery range from 5.5 V to 80/100 V, including load dump scenarios. Load dumps are automotive events where a running alternator loses its connection to the battery, causing a high-voltage transient surge that can damage vehicle’s electronics.

The converters will find homes in applications such as 48-V motor control, advanced driver-assistance systems (ADAS), telematics, infotainment, body control, instrument clusters, and lighting systems.

Constant on-time (COT) control built into the devices maintains a nearly constant switching frequency (300 kHz). This technique results in fast load/line transient response, loop stabilization, and low output voltage ripple, making the converters easier to incorporate due to fewer external components. 

The proprietary gate-driver arrangement in these devices reduces switch-node ringing effects without sacrificing the turn-on and turn-off times of the N-channel MOSFET switch. It helps reduce the high-frequency radiated electromagnetic-interference (EMI) noise normally associated with MOSFET switching.

Power Protection Measures

Overcurrent protection (OCP) with frequency foldback mode ensures high load-current support while reducing junction temperature under fault conditions. An overtemperature protection (OTP) circuit immediately shuts down the controller’s output voltage at 160°C. When the temperature drops below the 140°C safety threshold, the converter automatically restarts. These protection features prevent controller damage or malfunction, maximizing system reliability.

The AP6A255Q/AP6A355Q, for example, is an internally compensated, standard DC-DC buck converter with a default frequency of 300 kHz. The device integrates a 500-mΩ high-side power MOSFET to provide efficient step-down DC-DC conversion.

Automotive-grade products are products with a Q suffix, meaning they have passed the rigorous AECQ reliability standard. They can be supplied on request with a Production Part Approval Process (PPAP), a set of documents provided by suppliers that contain detailed testing, quality, and reliability information for automotive-grade devices as specified by the Automotive Industry Action Group (AIAG).

Automotive-grade Q-suffix parts are manufactured in facilities certified to IATF 16949:2016, a technical specification for automotive sector quality management systems. It applies to the design/development, production and servicing of automotive-related products. The spec is supplemental to ISO 9001:2015.

Buck-Converter Demo Board

Diodes Inc. also offers engineers the DDB115R1 Demo Board, which showcases the AP68255Q, AP68355Q, AP6A255Q, and AP6A355Q DC-DC buck converter family as well as the AP74700AQ ideal-diode controller, plus the use of an EMI input filter. 

The board demonstrates a system-level solution with reverse-voltage protection, ISO 7637-2 transient pulse protection (using a suitable TVS), EMI filtering that passes CISPR 25 Class 5, as well as the DC-DC buck converter. 

The input filter contains a common-mode choke with capacitors on either side of it in a Pi configuration. This is connected in series with an LC low-pass filter containing an inductor and capacitor. The combination makes the board CISPR 25 class 5 compliant, which sets the guidelines for measuring radio disturbances in vehicles, boats, and electrical components.

The AP68255Q/355Q and AP6A255Q/355Q asynchronous buck converters are available in the thermally enhanced SO-8EP package; operating temperature range is −40 to +125°C. The devices are priced at $0.80 (AP68255Q), $0.86 (AP68355Q), $0.90 (AP6A255Q), and $0.96 (AP6A355Q) in 1,000-piece quantities. Standard-compliance versions are also available for industrial and commercial applications.

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