RBBA3000 series: 3kW and smaller than a half a chocolate bar

RECOM RBBA3000 series on blue background
The RBBA3000 from RECOM is a 3kW boost/buck converter in a half-brick package. The boost-buck technology offers an input voltage range of 9V to 60V at a current of up to 50A. It is the ideal solution for vehicle on-board networks with, for instance, a second on-board circuit in addition to a 12V one. The RBBA3000 is equally suitable for use in battery-powered devices or UPSs (uninterruptable power supplies). In the event of a power failure, it can be used to supply a robot with a 48V battery to help it complete its current task and subsequently return to a safe position.

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.

Efficiency vs. Output Current Graph
Fig. 1: Efficiency over output current

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 Ua can be set with a trim resistor Rtrim, based on the following calculation:
Minimum resistance formula with voltage and resistances
If Rtrim is set, the output voltage can be calculated as follows:
Voltage equation with resistances and drop.
Alternatively, the output voltage can be set by applying a specific voltage to the trim pin. This voltage is determined as follows:
Voltage equation
When voltage Utrim 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.

Graphs of Utrim and Rtrim functions

Fig. 2: Setting output voltage

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:
Equation for resistance involving maximum current
The maximum output current can also be controlled by voltage UItrim at the Iset pin. The following relevant calculation and the voltage is also adjustable, similar to the voltage settings explained:
Root mean square voltage calculation

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:

Linear relationship between current and voltage
Fig. 3: Current signal based on actual current

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:
Electrical circuit diagram with components
Fig. 4: EMC input and output filters
  • 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:

Signal spectrum with multiple peaks


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:

Electrical circuit diagram with labeled components

Fig. 6: 12V output voltage from variable input voltage

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

  • Input voltage: 9V to 60V (80V short time)
  • Output voltage: adjustable from 0V to 60V
  • Input and output current: 50Amax; adjustable current limitation/regulation
  • Efficiency: 96%, see Fig. 1
  • Power dissipation: 47W@Ue = 48V, Ua = 24V, Ia = 50A
  • Case: half-brick, 63.2mm x 60.6mm x 13.0mm, volume = 50cm³
  • Cooling: heat dissipation through baseplate, soldered or screwed
  • Reliability: MTBF according to Telcordia SR332, calculated for 1,3 x 106 hours
  • Comprehensive ambient tests: RECOM sources
  • Temperature range (with cooling): -40°C to +85°C
  • Galvanic insulation: input and output grounds connected
  • RECOM sources: data sheet, application notes, standards
Applications
  Series
1 DC/DC, 3000.0 W, Single Output, THT RBBA3000 Series
Focus
  • Non-isolated buck/boost converter
  • Up to 3000W in half brick case
  • Adjustable output voltage and current
  • Efficiency up to 96%