ROHM Semiconductor
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Smart Low-Side Switches Cut Power Loss, Can Replace Relays and MOSFETs

March 2, 2023
ROHM’s new series of 1- and 2-channel, 40-V intelligent low-side switches are designed for automotive and industrial applications, especially systems such as car body control, and engine and transmission control units.

Global issues (calls to reduce vehicle CO2 emissions to slow global warming) and trends (progress toward autonomous driving) are resulting in more complex architectures that demand increased levels of safety and robustness. Conventional discrete solutions involving mechanical relays or MOSFETs can no longer meet these requirements and are unable to provide the necessary protection against system failures.

With demand for high integration, added safety features, built-in intelligence, and diagnostic capability, intelligent power devices (IPDs), also called smart switches, have become an essential part of electronic automotive systems.

IPDs can be directly interfaced to a microcontroller and provide feedback (Fig. 1). They will replace MOSFETs, relays, or fuses and are suitable to drive/switch any resistive, inductive, capacitive, or LED type of load. Built-in protection circuits are capable of absorbing energy.

On that front, ROHM Semiconductor announced a new generation of single- and dual-channel 40-V smart low-side switches: the BV1LExxxEFJ-C and BM2LExxxFJ-C series. Built for automotive and industrial applications, the AEC-Q100-qualified devices are well-suited for systems such as car body control, engine and transmission control units, LED lighting modules, and other automotive electrical systems.

The intelligent low-side devices can switch currents for any type of resistive, capacitive, or inductive loads. When switching off an inductive load, the power MOSFET inside the smart switch needs to dissipate all of the magnetic energy stored previously in the inductor’s magnetic field. During this time, the device protects itself by actively clamping the voltage to a safe level. The power dissipated generates heat that’s distributed on the integrated power MOSFET’s surface.

ROHM’s new products are said to be the industry’s first to combine heat suppression with low on-resistance, which is difficult to achieve in a compact size. The number of current-carrying channels are optimally controlled using a proprietary thermally distributed active clamp control (TDACC) circuit, which occurs when the power MOSFET in the smart switch generates heat due to back EMF during a turn-off event. TDACC, a trademark of ROHM, offers increased integration capability, allowing ROHM to present the industry’s first dual-channel 40-mΩ (on-resistance) product in the compact SOP-J8 package (Fig. 2).

A wide range of on-resistance values (40/80/160/250 mΩ) in both single- and dual-channel configurations are offered to meet diverse needs. Furthermore, the contact discharge tolerance of all products in the family is higher than that of other standard products. This adds to safer operation inside various electronic equipment types.

The parts feature integrated overcurrent and overvoltage protection, built-in diagnostic features, and rapid temperature rise detection. An active clamp circuit protects the IPD from counter-electromotive force (electromagnetic inductive energy from coils, actuators, etc.), and a self-turn-on prevention circuit prevents momentary malfunctions during frequently occurring rapid battery rise.

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