Instead of spending money on ready-made modules, manufacturers refer to the application circuit of the control IC, use discrete devices to build a switching regulator and install it on the circuit board. This method is effective in theory, but there are some problems in practice.

On the surface, to obtain a fully functional switching regulator, you only need to install the latest generation 2x2mm control IC on the printed circuit board together with the discrete devices recommended by the manufacturer. This also sounds logical. In theory alone, this should also be the lowest cost to make the equipment operate efficiently. Unfortunately, after practice, I found that things are not so simple, because details determine success or failure.

Handling dynamic loads

The circuit designs proposed by chip manufacturers are usually based on a somewhat optimistic assumption that most loads are static, so these designs have few discrete devices. In fact, static loads are often an exception to normal functions. Load cycles with a ratio of 1:1 million are very common, such as when the microcontroller switches to sleep mode.

SMD switching regulator module shortens development cycle

As shown in the above formula, the excess energy causes the voltage in the capacitor to increase rapidly. At first, the controller switches the on time to zero. If the inductor still has some energy at this time, the output voltage can no longer be well controlled. In devices with low output voltage, it may also double unless the capacitance is much greater than the recommended value in the specification.

SMD switching regulator module shortens development cycle

Discrete device solutions are not easy to overcome this problem. In the RPM series design, there are six shunt capacitors to buffer the output (Figure 1), which is far beyond the chip manufacturer’s recommendations. This configuration is standard for all models in recom’s new RPM series. Through several small ceramic capacitors in parallel, the surface area can be much larger than using a single large capacitor. Therefore, heat can be conducted more effectively from IC and inductor to GND plane. Another advantage of this design is to reduce the ESR of the capacitor.

How to improve EMC

Although the above method can overcome the dynamic load problem of discrete device design, EMC brings greater challenges, because the performance of the filter is determined not only by the controller IC, but also by the layout of the whole printed circuit board. This is why IC manufacturers usually do not provide advice. Because device designers usually know little about the interaction between IC and PCB, they cannot predict whether the circuit will pass EMC test.

SMD switching regulator module shortens development cycle

As designers need to reduce the size of inductors, the EMC problem of high switching frequency becomes more and more important. Joseph Fourier showed that square waves can be presented as infinite sine waves with higher frequencies. The higher the switching frequency, the greater the number of harmonics, so the possibility of resonance affecting inductors and capacitors in PCB is higher.

SMD switching regulator module shortens development cycle

Figure 3: rpm5 0-6.0 electromagnetic radiation; RPM5. 0-6.0 is equipped with class B external filter, as recommended in the data manual.

The power module is an EMC optimized and certified product. For example, the module of recom RPM series is equipped with 4-layer PCB, and its bottom layer and metal shell provide appropriate shielding on six sides (Fig. 2). As a result, these modules provide excellent EMC data. The relevant specifications contain the information of simple SMD ferrite magnetic beads, which enable the module to reliably comply with Class A or class B specifications, which has been verified in the test of recom EMC laboratory (Fig. 3). If you can reliably control the quality of the main power supply and the distance between the load and the module, you may not even need to use magnetic beads.

Good thermal management requires 4 layers

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

4-layer plate is the most suitable solution because GND plane is used as radiator. For equipment with two layers enough to carry all components, it is more economical to use ready-made modules. For example, recom’s RPM family has optimized thermal management capabilities.

In the recom R & D laboratory in gmondon, engineers spent months developing a solution combining the best electronic design with the best heat dissipation design. Now the 12X12MM circuit board of RPM module has many advanced heat dissipation functions, including various vias designed as heat pipes. Although this technology is not cheap, it ensures that the heat of BGA IC and passive components is radiated to the metal shell and GND plane in the most uniform way.

With this innovative approach, recom has once again set a new global standard because the RPM module can work reliably at ambient temperatures up to 105 ° C without derating, with heat dissipation only through the housing and GND plane. The most powerful RPM module can provide up to 6A current, and the power density of 50W / cm3 is about 50% higher than that of similar modules provided by other suppliers.

Other advanced technical features

RPM series includes non isolated SMD switching regulator modules designed according to the latest technical standards. Currently, the module has 3.3V and 5V outputs and a current of 1, 2, 3 or 6a, and can be used in combination with external resistors to achieve an output voltage between 0.9V and 6.0V. Ultra thin module, with 97% to 99% ultra-high efficiency at full load. Especially in the load range of 5 to 20%, the module also has very high efficiency (Figure 4)

SMD switching regulator module shortens development cycle

Figure 4: in the actual test, the new switching regulator has achieved excellent efficiency in a very important low load range, — the maximum value is 99%!

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

SMD switching regulator module shortens development cycle

Evaluation board for shortening development cycle

Manufacturers can choose modules instead of discrete devices to design DC / DC converters and successfully develop prototypes. The latest RPM series has 25 pads, each only about 1mm2. In order to facilitate the evaluation of the prototype, recom has developed a special evaluation board, which can integrate the switching regulator and all its functions, and the external filter components have been installed. Therefore, all evaluations can be easily completed without welding.

SMD switching regulator module shortens development cycle

conclusion

Although the highly integrated controller IC makes it easier to produce non disconnector regulators, it is generally better to use off the shelf modules. On the one hand, the module shortens 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, and there is no need to purchase separate components from different suppliers. Finally, it is also important that they no longer need to mount controller chips with a size of less than 2mm2 on the PCB. Mounting chips is not an easy task, but it is a great challenge to mount chips next to larger components.

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