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ROHM’S Isolated DC-DC Converters for xEV Reduce Application Size and efforts for noise design countermeasure

2023-01-25 | Return

Contributes to smaller mounting area in isolation circuit by 30% compared with standard products

ROHM has recently developed an isolated flyback DC-DC converter, BD7Fx05EFJ-C (BD7F105EFJ-C, BD7F205EFJ-C) optimized for gate drive power supplies in xEV applications such as electric compressors, and PTC heaters.

In recent years, xEVs such as hybrid and electric vehicles have become increasingly popular as the industry moves towards achieving a sustainable society. xEVs, which primarily use electricity as their energy source, are equipped with unique applications such as, electric compressors for AC, and PTC heaters to raise the cabin temperature. And as these applications are driven by high voltages, it is necessary to isolate the primary circuit that includes the battery from the secondary circuit comprised of the motor and other systems to ensure safety. However, in addition to issues such as larger mounting area and power consumption, conventional isolated circuit configurations require considerable noise countermeasures for switching frequencies that vary with output current.

ROHM’s new product utilizes a circuit configuration that achieves stable switching frequency characteristics without requiring a photocoupler, decreasing application size together with workload for noise design countermeasure. Leveraging ROHM’s superior analog design technology allows the BD7Fx05EFJ-C to eliminate the need for photocouplers, transformer auxiliary windings, and peripheral components conventionally necessary to detect secondary-side voltage and current. On top, next to solving issues with photocouplers, such as large power consumption, fluctuating detection accuracy due to temperature, and deterioration over time, ROHM has also achieved greater miniaturization by reducing the number of components. As a result, it is possible to reduce the number of components – including the photocoupler – used for current detection by 10 (equivalent to a board area of 30%) compared to general isolated flyback power supply circuits.

The BD7Fx05EFJ-C is also equipped with an adaptive ON-time control function that fixes the switching ON time, ensuring a stable frequency of around 350kHz regardless of output power. To be complaint with the CISPR25 automotive EMC standard requires considerable noise design in the frequency range from 150kHz to 300kHz, but as ROHM’s new converters do not fall within this band, noise countermeasures can be greatly simplified. This, together with a spread spectrum function that minimizes radiated noise, contributes to reducing the number of efforts for noise design.

Going forward, ROHM will continue to develop products that contribute to greater miniaturization and lower noise by leveraging its strength in analog technology, helping to achieve a sustainable society.

Product Lineup

In addition to reducing the number of components and person-hours required for noise countermeasures, the BD7Fx05EFJ-C improves application reliability by incorporating multiple protection circuits along with a function that stabilizes the output voltage.

Part No.	Output Power [W]		Input Rated Voltage [V]	Input Voltage Range [V]		Allowable Switch Current [A]		Switching Frequency [kHz]
Part No.	Output Power [W]		Input Rated Voltage [V]	Input Voltage Range [V]		Allowable Switch Current [A]		Switching Frequency [kHz]
BD7F105EFJ-C		4W@V_IN=12V			45		3.4 to 42.0		2.6
BD7F205EFJ-C		6W@V_IN=12V			45		3.4 to 42.0		3.8

*1 Load Compensation Function: VF changes based on the output load of the secondary diode can cause the output voltage to drop.
Compensating for this output voltage drop stabilizes the output current-output voltage characteristics.
*2 Multiple protection functions: Input undervoltage protection, thermal shutdown, overcurrent protection, short-circuit protection, reference voltage terminal protection, battery short-circuit protection.

Application Examples

ROHM’s new DC-DC converter IC is ideal for gate driver power supplies that must be isolated from the battery for safety.
Automotive: electric compressors, PTC heaters, inverters
Industrial: Power supplies, PLC (Programable Logic Controller), inverters

Product Information

Applicable Part Nos: BD7F105EFJ-CE2, BD7F205EFJ-CE2
Evaluation Board information
Evaluation Board Part Nos：
BD7F105EFJ-EVK-001, BD7F205EFJ-EVK-001

Terminology

PTC (Positive Temperature Coefficient) Heater
Applications that perform heating in xEVs which do not have a conventional heat source (engine) as in gasoline or diesel vehicles. Electricity from the battery is applied to the heater element, which generates heat to warm the interior of the vehicle.

Flyback Method
A circuit type used to configure isolated power supplies. Suitable for applications up to 100W, this method is superior to others in terms of number of components and cost. Other forward methods exist, and the evolution of the devices that make up these methods has resulted in smaller, more efficient isolated power supplies.

Photocoupler
An electrical component consisting of an optical emitter that converts input electrical signals to light and a receiver (photosensor) that converts it back into electrical signals. The input and output sides are electrically isolated to prevent noise and electric shock from occurring while transmitting electrical signals.

CISPR25
An international standard for evaluating EMI (Electromagnetic Interference) emitted from components and modules. To prevent equipment malfunctions, noise must be kept within the specified limits for each frequency.

Spread Spectrum Function
A function that spreads the noise energy over a large frequency band through frequency hopping instead of using a fixed frequency. This reduces EMI by lowering the peak noise value.

Source: http://www.rohm.com/