DC-DC converters provide superior power efficiencies when compared to linear regulators but one of their biggest drawbacks for designers is their noisy nature. Diodes Incorporated has just released a new range of DC-DC modules that aims to address EMI reduction.

 

A Quick Overview of DC-DC Converters

Before DC-DC converters became commonplace in consumer products, the go-to power regulation method was with the use of linear regulators with one of the most famous being the 7805 5V regulator. While these regulators are simple, cheap, and effective, they have one serious issue: they have the potential to waste large amounts of energy.

For example, if the 7805 regulator is fed with 9V and regulates this down to 5V, then the difference in voltage, 4V, is what is internally dropped. If this same setup draws 100mA, then the wasted power due to this voltage drop is 4 x 0.1, which is equal to 0.4W. While this may not seem like much, it's more than enough to get the 7805 incredibly hot. In this case, it's  nearly the same amount of power being supplied to the external circuit, giving the 7805 an efficiency only slightly higher than 50%.

 

The famous 7805 is still in use today

 

A DC-DC converter, by comparison, is capable of reducing the voltage from a power source with the use of high-speed switching circuits, inductors, capacitors, and resistors without the need to dissipate large amounts of energy. Some DC-DC converters can have efficiencies between 80% to 95% and are often used in conjunction with a linear regulator to improve overall efficiency while retaining the benefits of DC switching and linear regulation.

However, DC-DC converters are not all perfect and their biggest downfall is a designer's worst nightmare: EMI.

 

DC-DC Converters and Switching Noise

For a DC-DC converter to work, power transistors are required to switch large voltages and currents quickly with quick rise and fall times (as shortening these reduces power consumption) but this switching generates many harmonics on a frequency spectrum that is related to the switching speed (see square waves and how they are comprised of many sine waves at odd frequencies).

 

Square waves are made up of many sine waves at odd harmonics

 

While this is not a problem for an individual performing an experiment or building a project it is a serious problem for anyone designing a product as FCC and CE have strict regulations on how much EM radiation a product is allowed to emit. To use DC-DC converters in a product an engineer must consider the switching frequency, the trace length, positioning of the components, stitching via, and rise/fall times

 

The AP6320x DC-DC Converters

This week, Diodes Incorporated announced the release of their newest DC-DC series of products, the AP6320x. These are buck converters capable of operation up to 2A.

Housed in a TSOT26 package, these devices are synchronous buck converters that can tolerate input voltages between 3.8V and 32V, integrates a 125mΩ high side MOSFET and a 68mΩ low side MOSFET, and efficiencies as high as 88%.

While the converters operate at either 500kHz or 1.1MHz (depending on the device), they all integrate frequency spread spectrum (FSS) to reduce EMI, as well as proprietary gate drivers that further reduce EMI generated by the internal power MOSFETs.

The frequency spread spectrum is achieved with the use of a jitter of ±6% that prevents the switching frequency from being at any one frequency for an extended period of time.

 

Image courtesy of Diodes Incorporated 

 

Another method employed to further reduce EMI is that the pinout arrangement has been chosen so that the converter can be used on a single-sided PCB which removes the need for via which are a potential source of EMI. The converters require as few as four external components. While the AP63200 and AP63201 have a variable output (depending on a resistor combination), the AP63203 and AP63205 devices all have fixed outputs of 3V and 5V respectively. 

 

Image courtesy of Diodes Incorporated 

 

According to Diodes Incorporated, the AP6320x range of devices is suitable for many applications including gaming consoles, TVs, home audio equipment, network systems, FPGAs, DSPs, ASICs, and even electric vehicles.

 

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