Vicor Micro Family of DC-DC Converter - Manual (Page 15)

Design Guide & Applications Manual
For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies
Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com
Page 14 of 88
Apps. Eng. 800 927.9474 800 735.6200
3. Design Requirements
The fuse must be in series with the positive (+) Input lead.
Fusing the negative (–) Input lead does not provide adequate
protection since the PR and PC terminals of the converter
are referenced to the –Input. If a fuse located in the
–Input lead were to open, the PR and PC terminals could
rise to the potential of the +Input. This may damage any
converter or circuitry connected to these pins. The fuse
should not be located in an area with a high ambient
temperature as this will lower the current rating of the fuse.
THERMAL AND VOLTAGE HAZARDS
Vicor component power products are intended to be used
within protective enclosures. Vicor DC-DC converters work
effectively at baseplate temperatures, which could be
harmful if contacted directly. Voltages and high currents
(energy hazard) present at the terminals and circuitry
connected to them may pose a safety hazard if contacted
or if stray current paths develop. Systems with removable
circuit cards or covers which may expose the converter(s)
or circuitry connected to the converters, should have proper
guarding to avoid hazardous conditions.
The module pins are intended for PCB mounting either by
wave soldering to a PCB or by insertion into one of the
recommended PCB socket solutions. Use of discrete wire
soldered directly to the pins may cause intermittent or
permanent damage to the module; therefore, it is not rec-
ommended as a reliable interconnection scheme for pro-
duction as a final released product. In addition, modules
that have been soldered into printed circuit boards and
have subsequently been removed should not be reused.
PC PIN
The PC pin should be used only to; disable the module,
provide a bias to input referenced circuitry or communicate
status of the module. The PC pin is referenced to the –Input
pin. All circuits that connect to the PC pin must use the
–Input as the reference. Do not break the connection
between the –Input and the circuitry connected to the
PC pin or damage to the module will result. Additional
requirements include:
• Circuits that derive their power from the PC pin must
not exceed 1.5 mA.
• Do not drive the PC pin with external circuitry.
• Do not attempt to control the output of the converter
by PWM pulsing of the PC pin, or exceed a repetitive
on / off rate of 1 Hz.
For applications where the converter will be disabled on a
regular basis or where capacitance is added to this pin,
please contact Vicor
Applications Engineering .
HIGH-POWER ARRAYS AND PR PIN
To simplify the implementation of large arrays, a subset of
modules within the parallel array should be configured as
boosters (listeners) by connecting the SC pin to the –S pin.
Modules, which are configured as boosters, cannot assume
the role of drivers (talkers) for N+M redundant arrays.
Modules configured as boosters may be locally sensed.
Each module within the parallel array must be properly
bypassed with capacitors. Film or ceramic types should be
used across the input of the module and between each
input lead and the baseplate. Modules having input
sources, which are not connected to SELV sources, should
use X-capacitors across the input and Y-capacitors from
each input power pin to the baseplate. When in doubt
about capacitor safety approvals, always consult with the
governing safety regulatory agency or Vicor Applications
Engineering.
A maximum of 12 modules may be directly connected in
parallel. Please contact Vicor Applications Engineering for
assistance with larger arrays.
The PR pin is referenced to the –In pin; therefore, all
modules within the array must have a common low-
impedance connection between each –In pin. Special
precautions are necessary if a PCB is not used for inter-
connection of modules, because the wiring impedance
can be significant. Do not allow the connection between
the –In pin and the –In bus to become disconnected as
damage to the module will result.
Coupling transformers should be used to transmit the PR
pulse if long distances between each module are antici-
pated or if the interconnection impedance of the –In leads
is high or questionable. PR coupling transformer(s) should
be used if the PR pulse exits the PCB. For example, an
array constructed of multiple circuit cards plugged into a
backplane with a number of converters on each card
should have a PR coupling transformer at the entry point
of each card; however, no coupling transformer would be
required between each converter on the card of three or
less converters on a single PCB. Do not externally drive the
PR pin, connection to this pin is limited to Vicor module
application only.
INPUT SOURCE IMPEDANCE
The impedance of the source feeding the input of the
module directly affects both the stability and transient
response of the module. In general, the source impedance
should be lower than the input impedance of the module
by a factor of ten, from DC to 50 kHz.