Asynchronous Buck Converters Enhance Efficiency in Automotive 48-V POL Apps
What you’ll learn:
- The AP68255Q/AP68355Q and AP6A255Q/AP6A355Q incorporate 500-mΩ power MOSFETs to deliver with up to 3.5 A of continuous output current.
- These converters cover the full automotive battery range from 5.5 V to 80/100 V, including load-dump scenarios.
- They can be used in applications such as 48-V motor control, ADAS, telematics, infotainment, and more.
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.