3kW and smaller than a half a chocolate bar

Switching regulator that boosts and bucks

Its dimensions are 63.2mm x 60.6mm x 13.0mm, with a volume of 50cm³. This compact size is made possible by the exceptionally high efficiency of the converter, reaching 96% along a very flat characteristic over load.

This results in an excellent efficiency rating even at low loads. However, at a high power density, the converter needs to be cooled. This is done by dissipating heat through the soldered or screwed baseplate attached to the bottom of the half-brick case. The converter can thus be operated at full power at ambient temperatures and up to 85°C. Above this range, derating becomes an issue. At 25°C and 80% load, the MTBF calculated according to Telcordia SR332 is 1,3 x 106 hours.

Setting output voltage

In the RBBA3000, the output power U_a can be set with a trim resistor R_trim, based on the following calculation:


If R_trim is set, the output voltage can be calculated as follows:


Alternatively, the output voltage can be set by applying a specific voltage to the trim pin. This voltage is determined as follows:


When voltage U_trim is changed, the output voltage of the RBBA3000 is adjusted along the curve shown in figure 2. It is thus possible to regulate and control the output voltage within a range of 0V to 60V, using for instance a microcontroller and a DA, at an output current of up to 50A. The characteristics of these two control variables are shown in figure 2.

Current limitation

The maximum output current can be limited with a second resistor. It is connected to the Iset pin and is calculated as follows:


The maximum output current can also be controlled by voltage UItrim at the Iset pin. The rele-vant calculation is:


and the voltage is also adjustable, similar to the voltage settings explained above.

Current measurement

The RBBA3000 comes with a built-in current measuring function, doing away with the com-mon problems associated with current measurement in power electronics circuits. The volt-age at the Ishare pin provides the current signal, based on the characteristic shown below in figure 3:

Parallel circuit

For applications that require more than 50A, two RBBA3000-50 can be operated in parallel. To do this, the two Ishare pins must be connected to ensure equal current distribution to the two converters. In addition, the two converters must have the same settings for input voltage, output voltage, sense pins, etc. For further details, see the RECOM Application Guide.

EMC

The actual dimensioning of the input and output filters depends on the application, so we can only consider the worst case here. In order to meet the standards for conducted and radiated noise, we recommend the following filters for the RBBA3000:

• C1: 470μF/100V, electrolytic capacitor
• C2: 10μF/100V, ceramic capacitor
• C3: 10μF/100V, ceramic capacitor
• C4: 10μF/100V, ceramic capacitor
• L1: 10μH/56.7A, differential mode choke, e.g., Würth Elektronik 7443763540100
• LCM: 1.4mH/50A, common mode choke, Schurter Inc. DKIH-3252-506J-NK

Figure 5 shows the achieved spectrum of the connected noise:



The relevant volumes are 50cm³ for the RBBA3000, and 52cm³ and 87cm³ for the diff mode choke and the common mode choke, respectively. Depending on the actual application, some of the filter elements may be omitted.

Applications

We already briefly outlined the potential applications of the RBBA3000. Let us now look in more detail at an application where a variable input voltage (20–60V) needs to be converted into a regulated output voltage of 12V:

To achieve a different output voltage, the only component that needs to be changed is the 36kΩ resistor; see also figure 2.

Key data of the RBBA3000