PRELIMINARY
Single Output
RBC Models
48V
IN
, 12V/25A Output
Quarter Brick, Regulated Bus Converter
Features
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Up to 300 Watts total output power
To 93% Ultra-high efficiency @ full load
48V Input ( up to 36-75V range)
12V/25A Output for Intermediate Bus
Architectures with POL converters
Synchronous-rectifier topology
300kHz fixed switching frequency
Fully isolated, 1500V (BASIC)
Low 35mVp-p ripple/noise
2.3" x 1.45" x 0.39" quarter brick
Stable no-load condition
Thermal shutdown
Fully I/O protected
IEC/EN/UL/cUL60950 certification
pending
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Optimized for distributed power Intermediate Bus Architectures (IBA), the RBC-
12/25-D48 DC/DC bus converter series offer partially regulated outputs (±2.5%,
line and load) in an industry-standard quarter brick open frame package at excel-
lent prices. The present trend in distributed power architectures (DPA) requires both
high efficiency and some regulation of the output voltage to reduce the risk of under
voltage dropout. Earlier unregulated bus converters were simply ratiometric “DC
transformers.”
The fully isolated (1500Vdc) RBC series accept a wide range 36 to 75 Volt DC
input (48V nominal) and convert it to an output of 12Vdc at 25 Amps maximum. This
output then drives point-of-load (POL) converters such as our LSN, LEN, LSM or
LQN series which feature precise load regulation. Applications include 48V-powered
datacom and telecom installations, base stations, cellular telephone repeaters and
embedded systems. Wideband output ripple and noise is a low 35mVp-p. Low overall
height of 0.39" (9.9 mm) fits tight card cages.
The RBC’s synchronous-rectifier topology and fixed frequency operation means
excellent efficiencies up to 93%, enabling “no heatsink” operation for most applica-
tions up to +70°C (400 LFM airflow). “No fan” or zero airflow applications may use the
optional base plate for cold surface mounting or natural-convection heatsinks.
A wealth of electronic protection features include input undervoltage (UV) lockout,
output current limit, short circuit hiccup, overtemperature shutdown and output
overvoltage. Available options include positive or negative polarity remote On/Off
control and the baseplate. Assembled using ISO-certified automated surface-mount
techniques, the RBC series includes all FCC, UL, and IEC emissions, safety and
flammability certifications.
Figure 1. Simplified Schematic
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RBC Series
Page 1 of 6
RBC Series
R E G U L AT E D D C / D C B U S C O N V E R T E R S
P A R T
N U M B E R
S T R U C T U R E
M E C H A N I C A L
S P E C I F I C A T I O N S
R BC
-
12
/
25
-
D48 N B
-
C
Regulated
Bus Converter
Nominal Output Voltage:
12 Volts
Maximum Rated Output:
Current in Amps
Input Voltage Range:
D48
= 36 to 75 Volts
(48V nominal)
Optional:
On/Off Control
N
= negative polarity
P
= positive polarity
Optional Baseplate
RoHS-6
compliant*
*
Contact C&D Technologies (Datel)
for availability.
Note:
Not all model number combinations are available.
Contact C&D Technologies for ordering assistance
CAUTION
– This converter is not internally fused. To avoid danger to
persons or equipment and to retain safety certification, the user must
connect an external fast-blow input fuse as listed in the specifications.
Be sure that the PC board pad area and etch size are adequate to
provide enough current so that the fuse will blow with an overload.
Start Up Considerations
When power is first applied to the DC/DC converter, there is some risk
of start up difficulties if you do not have both low AC and DC imped-
ance and adequate regulation of the input source. Make sure that your
source supply does not allow the instantaneous input voltage to go
below the minimum voltage at all times. Even if this voltage depression
is very brief, this may interfere with the on-board controller and pos-
sibly cause a failed start.
Use a moderate size capacitor very close to the input terminals. You
may need two parallel capacitors. A larger electrolytic or tantalum cap
supplies the surge current and a smaller parallel low-ESR ceramic cap
gives low AC impedance.
Remember that the input current is carried both by the wiring and the
ground plane return. Make sure the ground plane uses adequate thick-
ness copper. Run additional bus wire if necessary.
I/O Connections
Pin
Function P65
1
–Input
2
Remote On/Off
3
+Input
4
–Output
5
+Output
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RBC Series
Page 2 of 6
R E G U L AT E D D C / D C B U S C O N V E R T E R S
RBC Models
Performance/Functional Specifications
Typical at T
A
= +25°C under nominal input voltage and full-load conditions unless noted.
Refer to required airflow and Derating curves for thermal specifications. [1]
Operating Temperature Range
(With Derating)
Storage Temperature Range
Relative Humidity
Safety Compliance
Electromagnetic Interference
(may require external filters)
Outline Dimensions
Pin Material
Weight
See Derating curves
–55 to +125°C
To 85% / +85°C
UL60950, CSA-C22.2 No.60950,
IEC/EN60950
FCC part 15, EN55022, conducted
or radiated
Input
Input Voltage Range
Recommended External Fuse
Start-up Threshold
Undervoltage shutdown
Overvoltage shutdown
Input Current, nominal
Input Current, V
IN
= V
MIN
Input Current, shut-down mode
Inrush Transient
Reflected Ripple Current
[2]
Internal Filter Type
Reverse Polarity Protection
Remote On/Off Control
[5]
Positive Logic
Negative Logic
Current
Total Output Power
[3]
Setpoint Accuracy
(50% load)
Extreme Accuracy
[14]
Output Current
[7]
Minimum Load
Ripple and Noise
(20MHz bandwidth)
Line and Load Regulation
[10]
Efficiency
Isolation Voltage
(Input/output)
(Input to baseplate)
(Baseplate to output)
Isolation Resistance
Isolation Capacitance
Isolation Safety Rating
Current Limit Inception
(98% of V
OUT
)
Short Circuit Current
[6]
See ordering guide
20 Amp fast blow
35.5V
34.0V min., 38.5 V max.
None [note 12]
See ordering guide
9.14 Amps max.
2mA max.
0.05A
2
-seconds
10mAp-p
Pi filter
None (see note 11)
On = +3.5 to +13.5 V.
Off = Gnd. Pin or 0 to +1V.
On = Gnd. Pin or 0 to +1V.
Off = Pin open or +3.5V to +13.5V.
2mA max.
Physical
See mechanical specifications
Copper alloy over nickel underplate
1 ounce (28.4 grams)
Absolute Maximum Ratings
Input Voltage:
Continuous
Transient (100msec max.)
Input Reverse-Polarity Protection
Output Current
➈
75 Volts
100 Volts
None, see notes
Current limited. Devices can
withstand an indefinite output short
circuit without damage.
–55 to +125°C
+280°C
Output
306 Watts max.
±2% of V
NOMINAL
11.4V min. to 12.6V max.
See ordering guide
No minimum load
See ordering guide [8]
See ordering guide
See ordering guide
1500Vdc min.
1500Vdc min.
1500Vdc min.
100MΩ
1000pF
Basic
30 Amps after warm up
5 Amps
(hiccup autorestart – remove short for
recovery)
Continuous, no damage
15Vdc max. via magnetic feedback
±0.02% per °C
Storage Temperature
Lead Temperature
(soldering, 10 sec.)
These are stress ratings. Exposure of devices to any of these conditions may adversely
affect long-term reliability. Proper operation under conditions other than those listed in the
Performance/Functional Specifications Table is not implied.
Short Circuit Duration
(+V
OUT
grd)
Overvoltage Protection
Temperature Coefficient
Dynamic Load Response
(to within 2% of V
OUT
)
Start Up Time
(V
IN
to V
OUT
regulated)
(Remote On to Vout regulated)
Fixed Switching Frequency
Calculated MTBF
[4]
Operating PCB Temperature
[13]
Electronic Thermal Shutdown
Max. Capacitive Loading
(resistive load) 10,000µF, low ESR 0.02 Ohms
Dynamic Characteristics
500µsec, 50-75-50% load step
60msec
20msec
300kHz
Environmental
TBD
+120°C max.
+125°C min.
Operating Temperature Range
[9]
–40 to +70°C
(No derating, full power, 400 LFM airflow, vertical mount)
(1) All models are tested and specified with 400 LFM airflow, external 1 || 10µF ceramic/tantalum
output capacitors and no external input capacitor. All capacitors are low ESR types. These
capacitors are necessary to accommodate our test equipment and may not be required to
achieve specified performance in your applications. All models are stable and regulate within
spec under no-load conditions.
General conditions for Specifications are +25°C, V
IN
= nominal, V
OUT
= nominal, full load.
(2) Input Ripple Current is tested and specified over a 5 Hz to 20 MHz bandwidth. Input filtering
is C
IN
= 33µF/100V tantalum, C
BUS
= 220µF/100V electrolytic, L
BUS
= 12µH.
(3) Note that Maximum Power Derating curves indicate an average current at nominal input
voltage. At higher temperatures and/or lower airflow, the DC/DC converter will tolerate brief
full current outputs if the total RMS current over time does not exceed the Derating curve. All
Derating curves are presented at sea level altitude. Be aware of reduced power dissipation
with increasing density altitude.
(4) Mean Time Before Failure is calculated using the Telcordia (Belcore) SR-332 Method 1, Case
3, ground fixed conditions, T
PCBOARD
= +25°C, full output load, natural air convection.
(5) The On/Off Control may be driven with external logic or by applying appropriate external
voltages which are referenced to Input Common. The On/Off Control Input should use either
an open collector/open drain transistor or logic gate which does not exceed +13.5V.
(6) Short circuit shutdown begins when the output voltage degrades approximately 2% from the
selected setting.
(7) The outputs are not intended to sink appreciable reverse current. Sinking excessive reverse
current may damage the outputs.
(8) Output noise may be further reduced by adding an external filter. See I/O Filtering and Noise
Reduction.
(9) All models are fully operational and meet published specifications, including “cold start” at
–40°C.
(10) Regulation specifications describe the deviation as the line input voltage or output load cur-
rent is varied from a nominal midpoint value to either extreme.
(11) If reverse polarity is accidentally applied to the input, a body diode will become forward
biased and will accept considerable current. To ensure reverse input protection with full
output load, always connect an external input fuse in series with the +V
IN
input. Use approxi-
mately twice the full input current rating with nominal input voltage.
(12) Input overvoltage shutdown on 48V input models is normally deleted in order to comply with
certain telecom reliability requirements. These requirements attempt continued operation
despite significant input overvoltage.
(13) Note that the converter may operate up to +120°C PCB temperature with the baseplate
installed. However, thermal self-protection occurs near +125°C and there is a temperature
gradient from high power components. Therefore, +100°C baseplate temperature is recom-
mended to avoid thermal shutdown.
(14) “Extreme accuracy” refers to all combinations of line and load regulation, output current,
inititial setpoint accuracy and temperature coefficient.
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RBC Series
Page 3 of 6
RBC Series
R E G U L AT E D D C / D C B U S C O N V E R T E R S
T E C H N I C A L
N O T E S
Input Fusing
Most applications and or safety agencies require the installation of fuses at
the inputs of power conversion components. The RBC-12/25-D48 Series may
have an optional input fuse. Therefore, if input fusing is mandatory, either
a normal-blow or a fast-blow fuse with a value no greater than twice the
maximum input current should be installed within the ungrounded input path
to the converter.
As a rule of thumb however, we recommend to use a normal-blow or slow-
blow fuse with a typical value of about twice the maximum input current,
calculated at low line with the converter's minimum efficiency.
Input Overvoltage and Reverse-Polarity Protection
The RBC-12/25-D48 does not incorporate input reverse-polarity protection.
Input voltages in excess of the specified absolute maximum ratings and input
polarity reversals of longer than "instantaneous" duration can cause perma-
nent damage to these devices.
Start-Up Time
The V
IN
to V
OUT
Start-Up Time is the interval between the time at which a
ramping input voltage crosses the lower limit of the specified input voltage
range and the fully loaded output voltage enters and remains within its
specified accuracy band. Actual measured times will vary with input source
impedance, external input capacitance, and the slew rate and final value of
the input voltage as it appears to the converter.
The On/Off to V
OUT
Start-Up Time assumes the converter is turned off via
the On/Off Control with the nominal input voltage already applied to the con-
verter. The specification defines the interval between the time at which the
converter is turned on and the fully loaded output voltage enters and remains
within its specified accuracy band.
Output Reverse Conduction
Many DC/DC's using synchronous rectification suffer from Output Reverse
Conduction. If those devices have a voltage applied across their output before
a voltage is applied to their input (this typically occurs when another power
supply starts before them in a power-sequenced application), they will either
fail to start or self destruct. In both cases, the cause is the "freewheeling" or
"catch" FET biasing itself on and effectively becoming a short circuit.
I/O Filtering and Noise Reduction
The RBC-12/25-D48 is tested and specified with external output capacitors.
These capacitors are necessary to accommodate our test equipment and
may not be required to achieve desired performance in your application. The
RBC-12/25-D48 is designed with high-quality, high-performance
internal
I/O
caps, and will operate within spec in most applications with
no additional
external components.
In particular, the RBC-12/25-D48 input capacitors are specified for low ESR
and are fully rated to handle the units' input ripple currents. Similarly, the
internal output capacitors are specified for low ESR and full-range frequency
response.
In critical applications, input/output ripple/noise may be further reduced using
filtering techniques, the simplest being the installation of external I/O caps.
External input capacitors serve primarily as energy-storage devices. They
minimize high-frequency variations in input voltage (usually caused by IR
drops in conductors leading to the DC/DC) as the switching converter draws
pulses of current. Input capacitors should be selected for bulk capacitance
(at appropriate frequencies), low ESR, and high rms-ripple-current ratings.
The switching nature of modern DC/DC's requires that the dc input voltage
source have low ac impedance at the frequencies of interest. Highly inductive
source impedances can greatly affect system stability. Your specific system
configuration may necessitate additional considerations.
Figure 2. Measuring Input Ripple Current
The RBC-12/25-D48 will withstand higher external sources several volts
above the nominal output. However, if there is a chance of consistent over-
voltage, users should provide an external voltage clamp or other protection.
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RBC Series
Page 4 of 6
R E G U L AT E D D C / D C B U S C O N V E R T E R S
RBC Models
Undervoltage Shutdown
When the input voltage falls below the undervoltage threshold, the converter
will terminate its output. However, this is not a latching shutdown mode. As
soon as the input voltage rises above the Start-Up Threshold, the converter
will restore normal operation. This small amount of hysteresis prevents most
uncommanded power cycling. Since some input sources with higher output
impedance will increase their output voltage greater than this hysteresis as
soon as the load is removed, it is possible for this undervoltage shutdown to
cycle indefinitely. To prevent this, be sure that the input supply always has
adequate voltage at full load.
Thermal Considerations and Thermal Protection
The typical output-current thermal-derating curves shown below enable
designers to determine how much current they can reliably derive from each
model of the RBC-12/25-D48 under known ambient-temperature and air-flow
conditions. Similarly, the curves indicate how much air flow is required to reli-
ably deliver a specific output current at known temperatures.
The highest temperatures in RBC-12/25-D48's occur at their output inductor,
whose heat is generated primarily by I
2
R losses. The derating curves were
developed using thermocouples to monitor the inductor temperature and
varying the load to keep that temperature below +110°C under the assorted
conditions of air flow and air temperature. Once the temperature exceeds
+125°C (approx.), the thermal protection will disable the converter using the
hiccup shutdown mode.
concept offers significantly lower cost, higher efficiency and therefore lower
temperatures, better reliability and longer service life. Bulky, expensive heat
sinks are eliminated and even a costly fan can be downsized or deleted.
To achieve these results, the isolation is concentrated in the bus converter
and the precise voltage regulation resides in the POL converters. Since
the high current power switching is located in the bus converter, designers
can arrange the best possible noise shielding, isolation layout and thermal
distribution. And, since most of the regulation is placed in the POL convert-
ers, the total system offers very high efficiency, important for battery-operated
and standby applictions. Typically, DATEL’s surface mount POL converters
are actually smaller than equivalent linear regulators, heat sinks and their
discrete components. Another benefit to the distributed power architecture is
that it eliminates digital crosstalk in tightly packed systems.
A further advantage is that multiple power voltages are implemented simply
by connecting POL’s with different output voltages. Today’s modern systems
require several low power voltages. Many large ASIC’s, gate arrays and
programmable logic are powered from 3.3 Volts or lower. CPU’s use 2.5 or
lower voltages at considerable current. And legacy logic or I/O ports may run
from 5 Volts. It makes sense to provide separate power converters for each
of these sections. But they do not all need to be isolated, saving cost, board
area and heat buildup.
Thermal Shutdown
Extended operation at excessive temperature will initiate overtemperature
shutdown triggered by a temperature sensor inside the PWM controller. This
operates similarly to overcurrent and short circuit mode. The inception point
of the overtemperature condition depends on the average power delivered,
the ambient temperature and the extent of forced cooling airflow.
Figure 4. Equivalent Voltage Source Model
Remote On/Off Control
Figure 3. Intermediate Bus Architecture
Distributed Bus Architecture
A revolution is at hand for powering dedicated mixed circuit systems. Instead
of installing a single large isolated power supply or multiple isolated convert-
ers, the new architecture uses one isolated power bus converter driving mul-
tiple Point-of-Load non-isolated DC/DC converters which are positioned right
where the power load is needed. While conceptually similar to having a single
master power supply and distrubuted linear regulators, the bus converter
The RBC-12/25-D48 may be turned off or on using the external remote
on/off control. Allow at least 15 milliseconds for either transition. This terminal
consists of a digital input to the internal PWM controller athrough a protective
resistor and diode.
The on/off input circuit should be CMOS logic referred to the –Input power
terminal however TTL or TTL-LS logic will also work or a switch to ground. If
preferred, you can even run this using a bipolar transistor in “open collector”
configuration or an “open drain” FET transistor. You may also leave this input
unconnected and the converter will run whenever input power is applied.
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RBC Series
Page 5 of 6
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