75W, DUAL OUTPUT, MIXED-VOLTAGE DC/DC CONVERTERS
5V & 3.3V Outputs/Returns
The BCP Series outputs (pins 7 & 10) and returns (pins 6 & 9) are isolated
from the +VIN and –VIN inputs (pins 4 & 1) via a transformer and opto-coupled
The +5V Return (pin 6) and +3.3V Return (pin 9) are connected internal
to the DC/DC converter. Though the returns are common within the DC/DC
converter, the regulating control loop for each output is sensed directly at its
respective output and return pins. In order to maintain optimum regulation if
ground plane is not used, it is critical that PC board layouts also return each
output to its corresponding return pin.
Filtering and Noise Reduction
All BCP DC/DC Converters achieve their rated ripple and noise speciﬁcations
using the external input and output capacitors speciﬁed in the Performance/
Functional Speciﬁcations table. In critical applications, input/output noise may
be further reduced by installing additional external I/O caps. Input capacitors
should be selected for bulk capacitance, low ESR and high rms-ripple-current
ratings. Output capacitors should be selected for low ESR and appropriate
frequency response. All caps should have appropriate voltage ratings and be
mounted as close to the converters as possible.
The most effective combination of external I/O capacitors will be a function of
your particular load and layout conditions. Our Applications Engineers will be
pleased to recommend potential solutions and can discuss the possibility of
our modifying a device’s internal ﬁltering to meet your speciﬁc requirements.
Contact our Applications Engineering Group for additional details.
Certain applications and/or safety agencies may require the installation of
fuses at the inputs of power conversion components. Fuses should also be
used if the possibility of sustained, non-current-limited, input-voltage polarity
reversals exists. For DATEL BCP DC/DC Converters, you should use slow-
blow type fuses with values no greater than the following.
Fuses should be installed in the +Input line.
Input Overvoltage/Undervoltage Shutdown and Start-Up Threshold
Under normal start-up conditions, devices will not begin to regulate until
the ramping-up input voltage exceeds the Start-Up Threshold Voltage (35V
for "D48" models). Once operating, devices will not turn off until the input
voltage drops below the Undervoltage Shutdown limit (32V for "D48" models).
Subsequent re-start will not occur until the input is brought back up to the
Start-Up Threshold. This built-in hysteresis prevents any unstable on/off
situations from occurring at a single voltage.
Input voltages exceeding the input overvoltage shutdown speciﬁcation listed
in the Performance/Functional Speciﬁcations will cause the device to shut-
down. A built-in hysteresis (2V typical for "D24" models, 4V typical for
"D48" models) will not allow the converter to restart until the input voltage
is sufﬁciently reduced.
The VIN to VOUT start-up time is the interval between the time at which
a ramping input voltage crosses the turn-on threshold point 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 VOUT start-up time assumes the converter has its nominal input
voltage applied but is turned off via the On/Off Control. 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
On/Off Control (Standard feature)
The On/Off Control (pin 3) may be used for remote on/off operation. As shown
in Figure 1A, the control pin is referenced to the –Input (pin 1) and will be
pulled to a high state internally. The standard BCP converter (no sufﬁx) is
designed so that it is enabled when the control pin is left open and disabled
when the control pin is pulled low (to less than +0.6V relative to –Input).
Dynamic control of the on/off function is best accomplished with a mechanical
relay or an open-collector/open-drain drive circuit (optically isolated if
appropriate). The drive circuit should be able to sink approximately 1mA for
The on/off control function is designed such that the converter can be dis-
abled (pin 3 pulled low for no-sufﬁx models) while input power is ramping up
and then "released" once the input has stabilized.
For BCP converters conﬁgured with the negative-polarity option on the On/Off
Control pin ("N" sufﬁx added to part number), operation is opposite to that
described above. The converter is disabled when the On/Off Control pin is left
open and enabled when pulled low.
Figure 1A. No Sufﬁx
Figure 1B. "N" Sufﬁx
Sync Function (Optional feature)
In critical applications employing multiple switching DC/DC converters, it may
be necessary to intentionally synchronize the switching of selected converters.
The BCP Series offers an optional Sync function ("S" sufﬁx) in place of the
On/Off Control on pin 3. The Sync pin will self-conﬁgure as either a slave or
master, depending on the circuit application.