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DS_E48SR1R825_05222008
8
DESIGN CONSIDERATIONS
Input Source Impedance
The impedance of the input source connecting to the
DC/DC power modules will interact with the modules and
affect the stability. A low ac-impedance input source is
recommended. If the source inductance is more than a few
μH, we advise adding a 10 to 100 μF electrolytic capacitor
(ESR < 0.7 Ω at 100 kHz) mounted close to the input of the
module to improve the stability.
Layout and EMC Considerations
Delta’s DC/DC power modules are designed to operate in
a wide variety of systems and applications. For design
assistance with EMC compliance and related PWB layout
issues, please contact Delta’s technical support team. An
external input filter module is available for easier EMC
compliance design. Application notes to assist designers
in addressing these issues are pending release.
Safety Considerations
The power module must be installed in compliance with the
spacing and separation requirements of the end-user’s
safety agency standard, i.e., UL60950, CAN/CSA-C22.2
No. 60950-00 and EN60950: 2000 and IEC60950-1999, if
the system in which the power module is to be used must
meet safety agency requirements.
Basic insulation based on 75 Vdc input is provided
between the input and output of the module for the purpose
of applying insulation requirements when the input to this
DC-to-DC converter is identified as TNV-2 or SELV. An
additional evaluation is needed if the source is other than
TNV-2 or SELV.
When the input source is SELV circuit, the power module
meets SELV (safety extra-low voltage) requirements. If the
input source is a hazardous voltage which is greater than
60 Vdc and less than or equal to 75 Vdc, for the module’s
output to meet SELV requirements, all of the following
must be met:
The input source must be insulated from the ac
mains by reinforced or double insulation.
The input terminals of the module are not
operator accessible.
If the metal baseplate is grounded, one Vi pin
and one Vo pin shall also be grounded.
A SELV reliability test is conducted on the
system where the module is used, in
combination with the module, to ensure that
under a single fault, hazardous voltage does not
appear at the module’s output.
When installed into a Class II equipment (without
grounding), spacing consideration should be given
to the end-use installation, as the spacing between
the module and mounting surface have not been
evaluated.
The power module has extra-low voltage (ELV)
outputs when all inputs are ELV.
This power module is not internally fused. To
achieve optimum safety and system protection, an
input line fuse is highly recommended. The safety
agencies require a normal-blow fuse with 2A
maximum rating to be installed in the ungrounded
lead. A lower rated fuse can be used based on the
maximum inrush transient energy and maximum
input current.
Soldering and Cleaning Considerations
Post solder cleaning is usually the final board
assembly process before the board or system
undergoes electrical testing. Inadequate cleaning
and/or drying may lower the reliability of a power
module and severely affect the finished circuit board
assembly test. Adequate cleaning and/or drying is
especially important for un-encapsulated and/or open
frame type power modules. For assistance on
appropriate soldering and cleaning procedures,
please contact Delta’s technical support team.