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 220 to 470 μF electrolytic
capacitor (ESR < 0.1 Ωat 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, 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 20A 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.
H48SN28012_01172008
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