RBBA3000-50: High Current, Non-Isolated DC/DC Converter
May 25, 2023
The RBBA3000-50 is a high-current (50A) intelligent buck–boost converter based on an internal digital signal processor.
Get the whole Whitepaper now
Description
The RBBA3000-50 is a high-current (50A) intelligent buck–boost converter, utilizing an internal digital signal processor (DSP). The dedicated DSP controller enables additional features, making this product highly suitable for a variety of practical power supply applications, including purely analog systems. In addition to its fast response to transient loads, the DSP core supports a comprehensive set of output protections, including short circuit, adjustable output current limit, over-voltage fault protection, and over-temperature protection.
The input voltage range spans from 9V to 60VDC, with a 100ms surge withstand capability up to 80VDC. This wide input range makes the RBBA3000-50 ideal for battery-powered systems, including those using lead-acid or lithium-ion battery packs, where the charger supply voltage may surge if the battery load is disconnected suddenly. The converter also features an under-voltage lock-out (UVLO), which disables the converter if the input voltage drops below 6V (typ.).
A growing trend is moving away from AC uninterruptible power supplies (UPS) and toward DC-backed systems for ensuring functionality during power outages. Using an AC supply to charge a battery or supercapacitor energy storage device, and then using that stored energy to provide AC power during an emergency, is highly inefficient for maintaining continuity. The power losses in both the DC charging circuit and the AC inverter are significant, which limits most UPS systems to providing only a few minutes of backup power. This is typically enough for computers to shut down, but it is often insufficient for mechanical systems like robotics or assembly machines to complete tasks or safely return to a resting position. By contrast, using a high-current 48VDC system allows direct battery backup, providing enough power for even heavy industrial assembly plants to reset safely. The RBBA3000-50 is perfect for such applications, as it can deliver a stable 48V output from an input voltage that is equal to, higher, or lower than 48VDC.
The converter is housed in a standard half-brick case, with an aluminum baseplate that ensures efficient thermal bonding with a heatsink. With appropriate cooling, the RBBA3000-50 can operate at full load across the full industrial temperature range of -40°C to +85°C. The datasheet includes calculation examples to help determine the necessary power derating based on heatsink size or application altitude. Additionally, four threaded inserts are provided to securely mount the converter to both the PCB and the heatsink.
All power supplies must comply with strict limits for radiated and conducted EMI (electromagnetic interference). The RBBA3000-50 datasheet provides guidance on the necessary external EMC filtering to meet the EN55032 Class A standard.
The input voltage range spans from 9V to 60VDC, with a 100ms surge withstand capability up to 80VDC. This wide input range makes the RBBA3000-50 ideal for battery-powered systems, including those using lead-acid or lithium-ion battery packs, where the charger supply voltage may surge if the battery load is disconnected suddenly. The converter also features an under-voltage lock-out (UVLO), which disables the converter if the input voltage drops below 6V (typ.).
A growing trend is moving away from AC uninterruptible power supplies (UPS) and toward DC-backed systems for ensuring functionality during power outages. Using an AC supply to charge a battery or supercapacitor energy storage device, and then using that stored energy to provide AC power during an emergency, is highly inefficient for maintaining continuity. The power losses in both the DC charging circuit and the AC inverter are significant, which limits most UPS systems to providing only a few minutes of backup power. This is typically enough for computers to shut down, but it is often insufficient for mechanical systems like robotics or assembly machines to complete tasks or safely return to a resting position. By contrast, using a high-current 48VDC system allows direct battery backup, providing enough power for even heavy industrial assembly plants to reset safely. The RBBA3000-50 is perfect for such applications, as it can deliver a stable 48V output from an input voltage that is equal to, higher, or lower than 48VDC.
The converter is housed in a standard half-brick case, with an aluminum baseplate that ensures efficient thermal bonding with a heatsink. With appropriate cooling, the RBBA3000-50 can operate at full load across the full industrial temperature range of -40°C to +85°C. The datasheet includes calculation examples to help determine the necessary power derating based on heatsink size or application altitude. Additionally, four threaded inserts are provided to securely mount the converter to both the PCB and the heatsink.
All power supplies must comply with strict limits for radiated and conducted EMI (electromagnetic interference). The RBBA3000-50 datasheet provides guidance on the necessary external EMC filtering to meet the EN55032 Class A standard.
Set Output Voltage
The RBBA3000-50 defaults to an output voltage of approximately 1.3V if the output voltage trim resistor or trim voltage is not connected. This safety feature ensures that the converter's high output current capability does not damage the user's application during testing or in the event of a board fault. There are two methods for setting the output voltage: using an external resistor or applying an external trim voltage. The trim pin is continuously monitored by the internal DSP core, allowing dynamic output voltage adjustment. This capability enables the supply voltage to the application to be modified based on load or standby status, reducing overall power consumption.
Set Output Voltage Using a Fixed Resistor
The calculation is as follows:
RTrim = Trim Resistor Value [Ω]
Voutset = Trimmed Output Voltage [V]
For example, the following commonly used output voltage trim resistors could be used.
Based on the table above, a 50kΩ potentiometer could be used to manually adjust the output voltage over the range of 12V to 60V.
Fig. 1: Voutset
Voutset = Trimmed Output Voltage [V]
For example, the following commonly used output voltage trim resistors could be used.
| Trimmed Output | Trim Resistor (E96) [KΩ] |
|---|---|
| 12 | 35.7 |
| 15 | 28.0 |
| 24 | 15.0 |
| 36 | 7.15 |
| 48 | 3.01 |
| 60 | 0.392 |
Table 1: Required Output / Trim Resistor
Based on the table above, a 50kΩ potentiometer could be used to manually adjust the output voltage over the range of 12V to 60V.
Fig. 1: Voutset
Set Output Voltage Using an External Voltage
The output Voltage of the RBBA3000-50 can also be set using an external voltage. The calculation is as follows:
VsetU = External Voltage [V]
Vout,set = Required Output Voltage [V]
Fig. 2: Vout ext. Voltage control
An internal voltage reference will pull the trim pin to 2.5V if it is left floating. For stability, the output voltage responds to changes in the VsetU voltage with a slope of approximately 100mV/ms. While dynamic voltage adjustment is possible to accommodate varying operating conditions, the response time is not fast enough to support functions like dynamic signal envelope voltage tracking. However, if the application enters standby mode and the output voltage is reduced (e.g., from 24V to 12V to halve power consumption), the standby and wake-up times will be very quick.
Vout,set = Required Output Voltage [V]
Fig. 2: Vout ext. Voltage control
An internal voltage reference will pull the trim pin to 2.5V if it is left floating. For stability, the output voltage responds to changes in the VsetU voltage with a slope of approximately 100mV/ms. While dynamic voltage adjustment is possible to accommodate varying operating conditions, the response time is not fast enough to support functions like dynamic signal envelope voltage tracking. However, if the application enters standby mode and the output voltage is reduced (e.g., from 24V to 12V to halve power consumption), the standby and wake-up times will be very quick.
Output Current Limiting (Max Output Current)
The RBBA3000-50 has a default output current limit of 55A if the Iset pin (pin #4) is not connected. Therefore, if no output current limiting is required, the Iset pin can be left floating.
There are two methods for setting the output current limit (maximum output current): using an external fixed or variable resistor, or applying an externally set voltage. The Iset pin is continuously monitored by the internal DSP core, enabling dynamic output current limiting. This feature allows, for example, increasing the current limit to accommodate high start-up inrush currents, and then reducing it to protect the application from overload conditions. The current limiting function operates in hiccup mode, meaning if the output is overloaded or short-circuited, the output will be turned off temporarily, and the converter will attempt to restart.
There are two methods for setting the output current limit (maximum output current): using an external fixed or variable resistor, or applying an externally set voltage. The Iset pin is continuously monitored by the internal DSP core, enabling dynamic output current limiting. This feature allows, for example, increasing the current limit to accommodate high start-up inrush currents, and then reducing it to protect the application from overload conditions. The current limiting function operates in hiccup mode, meaning if the output is overloaded or short-circuited, the output will be turned off temporarily, and the converter will attempt to restart.
Set Output Current Limit Using a Fixed Resistor
The calculation is as follows:
RIset = Current limit set resistor (Ω)
Ioutset = Required output current limit (A)
For example, the following commonly used output current limit trim resistors could be used.
Based on the table above, a 33kΩ potentiometer in series with a 2R resistor could be used to manually adjust the output current limit over the range of 48A to 10A.
Fig. 3: RBBA3000-50 output current limit setting via RIset.
Ioutset = Required output current limit (A)
For example, the following commonly used output current limit trim resistors could be used.
| Required Limit [A] | Iset Resistor (E96) [KΩ] |
|---|---|
| 10 | 1.78 |
| 20 | 4.32 |
| 30 | 8.25 |
| 40 | 15.4 |
| 50 | 31.6 |
| 55 | floating |
Table 2: Required Current Limit / Iset Resistors
Based on the table above, a 33kΩ potentiometer in series with a 2R resistor could be used to manually adjust the output current limit over the range of 48A to 10A.
Fig. 3: RBBA3000-50 output current limit setting via RIset.
Set Output Current Limit Using an External Voltage
The output current limit of the RBBA3000-50 can also be set using an external voltage.
The calculation is as follows:
VsetI = External Voltage [V]
Iout,set = Required output current limit [A]
Fig. 4: RBBA3000-50 output current limit setting via VsetI.
This feature allows DAC control of the output current limit setting for dynamic current limiting.
Fig. 5: Ioutset DAC control
An internal voltage reference will pull up the Iset pin to 3.3V (Ioutset = 55A) if the pin is left disconnected. Therefore, if no output current limiting is required, the Iset pin should be left floating. For an example of how to use this feature to create a power-limited (constant-voltage) converter, refer to the next section.
The calculation is as follows:
Iout,set = Required output current limit [A]
Fig. 4: RBBA3000-50 output current limit setting via VsetI.
| Current Limit [A] | VsetI [V] |
|---|---|
| 5 | 0.25 |
| 10 | 0.5 |
| 20 | 1.0 |
| 30 | 1.5 |
| 40 | 2.0 |
| 50 | 2.5 |
| 55 | floating |
Table 3: Current Limit / VsetI
This feature allows DAC control of the output current limit setting for dynamic current limiting.
Fig. 5: Ioutset DAC control
An internal voltage reference will pull up the Iset pin to 3.3V (Ioutset = 55A) if the pin is left disconnected. Therefore, if no output current limiting is required, the Iset pin should be left floating. For an example of how to use this feature to create a power-limited (constant-voltage) converter, refer to the next section.
Current Share / Current Monitor
Current Monitor
The RBBA3000-50 has a dual-function current share/current monitor pin. In single converter applications, this pin can monitor the output load. The voltage generated by the converter will have a linear relationship with the output current.
Fig. 6: Imon
This function eliminates the need for an external shunt resistor to monitor the high-side current, thereby removing the drawbacks of power loss through the shunt and its temperature variation. Additionally, it eliminates the need for a high-current precision shunt resistor, amplifier, and current mirror, reducing associated costs.
Fig. 7: Current monitor cct
The Ishare output can also be connected to an ADC to interface the RBBA3000-50 with a microcontroller, enabling continuous load monitoring.
The following example shows ...
Fig. 6: Imon
This function eliminates the need for an external shunt resistor to monitor the high-side current, thereby removing the drawbacks of power loss through the shunt and its temperature variation. Additionally, it eliminates the need for a high-current precision shunt resistor, amplifier, and current mirror, reducing associated costs.
Fig. 7: Current monitor cct
The Ishare output can also be connected to an ADC to interface the RBBA3000-50 with a microcontroller, enabling continuous load monitoring.
The following example shows ...
Want to read the whole Whitepaper?
Applications
