Datasheet
UWQ-12/20-T48 Series
Wide Input, Isolated DOSA Quarter Brick DC-DC Converters
MDC_UWQ-12/20-T48 Series.A02 Page 24 of 29
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Input Fusing
Certain applications and/or safety agencies may require fuses at the inputs of
power conversion components. Fuses should also be used when there is the
possibility of sustained input voltage reversal which is not current-limited. For
greatest safety, we recommend a fast blow fuse installed in the ungrounded
input supply line.
The installer must observe all relevant safety standards and regulations. For
safety agency approvals, install the converter in compliance with the end-user
safety standard.
Parallel Load Sharing (S Option, Load Sharing)
Two or more converters may be connected in parallel at both the input and
output terminals to support higher output current (total power, see fi gure 2) or to
improve reliability due to the reduced stress that results when the modules are
operating below their rated limits. For applications requiring current share, follow
the guidelines below. The output voltage will decrease when the load current is
increased. Our goal is to have each converter contribute nearly identical current
into the output load under all input, environmental and load conditions.
Using Parallel Connections – Load Sharing (Power Boost)
All converters must be powered up and powered down simultaneously. Use
a common input power source.
It is required to use a common Remote On/Off logic control signal to turn on
modules (see fi gure 2).
When Vin has reached steady state, apply control signal to the all modules.
Figure 3 illustrates the turn on process for positive logic modules.
First power up the parallel system (all converters) with a load not exceed-
ing the rated load of each converter and allow converters to settle (typically
20-100mS) before applying full load. As a practical matter, if the loads are
downstream PoL converters, power these up shortly after the converter has
reached steady state output. Also be aware of the delay caused by charging
up external bypass capacitors.
It is critical that the PCB layout incorporates identical connections from each
module to the load; use the same trace rating and airfl ow/thermal environ-
ments. If you add input fi lter components, use identical components and layout.
When converters are connected in parallel, allow for a safety factor of at
least 10%. Up to 90% of max output current can be used from each module.
TECHNICAL NOTES
CAUTION: This converter is not internally fused. To avoid danger to persons or
equipment and to retain safety certifi cation, the user must connect an external
fast-blow input fuse as listed in the specifi cations. 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.
Using Parallel Connections – Redundancy (N+1)
The redundancy connections in fi gure 4 requires external user supplied
“OR”ing diodes or “OR”ing MOSFETs for reliability purposes. The diodes allow
for an uninterruptable power system operation in case of a catastrophic failure
(shorted output) by one of the converters.
The diodes should be identical part numbers to enhance balance between the
converters. The default factory nominal voltage should be suffi ciently matched
between converters. The OR’ing diode system is the responsibility of the user.
Be aware of the power levels applied to the diodes and possible heat sink
requirements.
Figure 2. Load Sharing Block Diagram
On/Off
On/Off
On/Off
F1
F2
F3
+
+
–
–
+
–
+Vin +Vout
–Vin –Vout
–Vin –Vout
–Vin –Vout
+Vin +Vout
+Vin +Vout
LOAD
Input
Source
On/Off Signal
Input
Filter
On/Off
Vout
Vin
CH2
CH2 = On/Off
CH3
CH3 = Vout
CH1
CH1 = Vin
Figure 3. Typical Turn On for Positive Logic Modules
Figure 4. Redundant Parallel Connections
On/Off
On/Off
On/Off
F1
F2
F3
+
+
–
–
+
–
+Vin +Vout
–Vin –Vout
–Vin –Vout
–Vin –Vout
+Vin +Vout
+Vin +Vout
LOAD
Input
Source
On/Off Signal
Input
Filter