Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency

Manufacturers are reluctant to spend money on off-the-shelf modules, but refer to the application circuit of the control IC and use discrete components to build a switching regulator mounted on the circuit board. This approach is theoretically valid, but in practice there are some problems.

Manufacturers are reluctant to spend money on off-the-shelf modules, but refer to the application circuit of the control IC and use discrete components to build a switching regulator mounted on the board. This approach is theoretically valid, but in practice there are some problems.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency

On the face of it, getting a fully functional switching regulator is all it takes to mount the latest generation 2x2mm control IC on a printed circuit board along with the manufacturer’s recommended discretes. This also seems to sound logical. In theory, this should also be the lowest cost to get the equipment running efficiently. Unfortunately, in practice, it turns out that things are not so simple, because the details make or break.

Handling dynamic loads

Circuit designs proposed by chipmakers are often based on the somewhat optimistic assumption that most loads are static, so these designs have very few discrete components. In practice, static loads are often an exception to normal functionality. Duty cycles with a ratio of 1:1 million are very common, such as when a microcontroller switches to sleep mode.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency

What happens to a switching regulator if the current required by the load drops from a few amps to a few µA in an instant? In this case, the built-in “intelligence” is no longer valid because the laws of physics are at work! The inductive energy generated on one half wave is transferred to the load on the next half wave. If the load suddenly drops to zero, energy can only be transferred to the output capacitor.

As shown in the above equation, the excess energy causes the voltage in the capacitor to rapidly increase. Initially the controller switches the on-time to zero. If the Inductor still has some energy at this point, the output voltage can no longer be well controlled. In low output voltage devices it may also be doubled unless the capacitance is much larger than the data sheet recommendations.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency
Figure 1: Measuring just 1.5cm2, RECOM’s RPM module board features 6 parallel capacitors at the output to withstand extreme duty cycles.

Discrete solutions do not easily overcome this problem. In the RPM series design, there are 6 parallel capacitors to buffer the output (Figure 1), which is far beyond the chip manufacturer’s recommendation. This configuration is standard on all models in RECOM’s new RPM series. With several small ceramic capacitors in parallel, you can get a much larger surface area than with a single large capacitor. Therefore, heat can be conducted more efficiently from the IC and inductor to the GND plane. Another advantage of this design is the reduced ESR of the capacitor.

How to improve EMC

While the above approaches can overcome the dynamic loading problem of discrete device designs, EMC presents a greater challenge because the performance of the filter is determined not only by the controller IC, but also by the layout of the entire printed circuit board. That’s why IC manufacturers usually don’t offer advice. Because device designers generally know very little about the interaction between the IC and the PCB, they cannot predict whether a circuit will pass EMC testing.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency
Figure 2: Modules of the RPM family conform to the DOSA second-generation high-density format. Metal case and GND plane provide 6-sided protection.

As designers need to reduce the size of inductors, the EMC issue of high switching frequencies becomes more important. Joseph Fourier showed that square waves can be represented as infinite sine waves at higher frequencies. The higher the switching frequency, the greater the number of harmonics and therefore the higher the likelihood that resonance will affect the inductors and capacitors within the PCB.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency
Figure 3: Electromagnetic emissions for RPM5.0-6.0; RPM5.0-6.0 is equipped with Class B external filter components as recommended in the data sheet.

The power module is a product that has been optimized and certified by EMC. Modules such as the RECOM RPM series are equipped with a 4-layer PCB with the bottom layer and metal casing providing proper shielding on six sides (Figure 2). Therefore, these modules provide excellent EMC data. The relevant data sheets have information on simple SMD ferrite beads that allow modules to reliably comply with either Class A or Class B specifications, which have been verified in tests in the RECOM EMC laboratory (Figure 3). Magnetic beads may not even be needed if the quality of the mains power supply and the distance between the load and the module can be reliably controlled.

Good thermal management requires a 4-layer board

Having successfully overcome all the issues just described, designers of discrete solutions now need to consider thermal issues. The compact design of modern controller ICs makes heat dissipation difficult. However, heat dissipation is critical for long service life and reliable ambient temperature values.

A 4-layer board is the most suitable solution because there is a GND plane as a heat sink. For devices where two layers are sufficient to carry all the components, it is more economical to use off-the-shelf modules. For example, RECOM’s RPM series features optimized thermal management.

In the RECOM R&D laboratory in Gmunden, engineers have spent months developing a solution that combines the best Electronic design with the best thermal design. Today’s 12x12mm boards for RPM modules have many advanced cooling features, including various vias designed as heat pipes. While this technique is not cheap, it ensures that heat from the BGA IC and passive components is dissipated in the most even way to the metal case and GND plane.

With this innovative approach, RECOM has once again set a new global standard, as the RPM module operates reliably at ambient temperatures up to 105°C without derating, with heat dissipation only through the case and GND plane. The most powerful RPM modules deliver up to 6A, >50W/cm3The power density is about 50% higher than comparable modules from other suppliers.

Other advanced technical features

The RPM series includes non-isolated SMD switching regulator modules designed according to the latest technology standards. Currently, modules have 3.3V and 5V outputs and currents of 1, 2, 3 or 6A, and can be combined with external resistors to achieve output voltages between 0.9V and 6.0V. Ultra-thin modules with ultra-high efficiency of 97% to 99% at full load. Especially in the load range of 5 to 20%, the module also has extremely high efficiency, (Fig. 4)

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency
Figure 4: In practical tests, the new switching regulator achieves excellent efficiency in the all-important low-load range—99% maximum!

The maximum allowable ambient temperature is also high, eg the 1A model without external cooling can withstand temperatures up to +107°C. Switching regulator modules have many additional features such as soft-start, timing, and output voltage tracking. Modules of the RPM series are manufactured in fully automated factories in Europe and can be ordered through normal distribution channels. The maximum price of the module is about 4 euros, the specific price will be adjusted according to the order quantity.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency

Evaluation boards that shorten development cycles

Manufacturers can choose DC/DC converters designed in modules rather than discrete components to develop prototypes smoothly. The latest RPM series has 25 pads, each pad is only about 1mm2. To facilitate prototype evaluation, RECOM has developed special evaluation boards that integrate the switching regulator with all its functions, with external filter components already installed. So all evaluations can be easily done without soldering.

Why SMD Switching Regulator Modules Can Improve Design Engineers’ Work Efficiency

in conclusion

Although highly integrated controller ICs can make it easier to produce non-isolated switching regulators, off-the-shelf modules are often the better choice. On the one hand, modules shorten the development cycle. On the other hand, they reduce the risk of EMC test failure. In addition, they are a single component in the bill of materials, eliminating the need to purchase discrete components from different suppliers. Last but not least, they no longer need to be mounted on a PCB with dimensions smaller than 2mm2controller chip. Mounting chips is not an easy task, but it is even more of a challenge when placing chips next to larger components.

The Links:   AT070TN07-VB LP133X5-A2IB

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