red camera is a another alternative which avoids the TC heatsinking effect.
But the IR camera must be calibrated frequently and accurately. Remember
too that it is quite diffi cult to accurately measure airfl ow right at the converter.
Murata Power Solutions uses a calibrated wind tunnel with large amounts
of data history. Because of thermal time constants, allow plenty of time for
temperature stabilization.
Trimming Output Voltages
These converters have a trim capability (pin 5) that allows users to adjust the
output voltage ±5%. Adjustments to the output voltage can be accomplished
via a trim pot, Figure 2, or a single fi xed resistor as shown in Figures 3 and 4.
A single fi xed resistor can increase or decrease the output voltage depend-
ing on its connection. Fixed resistors should have an absolute TCR less than
100ppm/°C to minimize sensitivity to changes in temperature.
A single resistor connected from the Trim (pin 5) to the +Output (pin 4), see
Figure 3, will decrease the output voltage. A resistor connected from the Trim
(pin 5) to Output Common (pin 6) will increase the output voltage.
Trim adjustment greater than 5% can have an adverse effect on the con-
verter's performance and is not recommended.
20kΩ
5-22
Tu rn s
+VIN
+VOUT
COMMON
TRIM
–VIN
ON/OFF
CONTROL
1
2
3
4
5
LOAD
6
+VIN
+VOUT
COMMON
TRIM
–VIN
ON/OFF
CONTROL
1
2
3
4
5
LOAD
6
R
TRIM DOWN
+VIN
+VOUT
COMMON
TRIM
–VIN
ON/OFF
CONTROL
1
2
3
4
5
LOAD
6
RTRIM UP
Figure 2. Trim Connections Using A Trim Pot
Figure 4. Trim Connections To Increase Output Voltage Using Fixed Resistors
Figure 3. Trim Connections To Decrease Output Voltage Using Fixed Resistors
Floating Outputs
Since these are isolated DC/DC converters, their outputs are "fl oating."
Designers will usually use the output Common (pin 6) as the ground/return of
the load circuit. You can, however, use the +Output (pin 4) as ground/return to
effectively reverse the output polarity.
Minimum Output Loading Requirements
1.2 to 5V models employ a synchronous-rectifi er design topology. All models
regulate within spec and are stable under no-load conditions. 12/15V models
employ a traditional forward architecture and require 10% loading (125mA for
12V models, 100mA for 15V models) to achieve their listed regulation specs.
12/15V models also have a minimum-load-for-stability requirement (20mA).
For 12/15V models, operation below 20mA or 10% loading will be stable but
regulation may degrade. A 100μF output capacitor is recommended below 10%
loading. Users should verify whether this relaxed regulation will have any effect
on output circuits. If so, add a small load of 10% or greater.
Operation under no-load conditions will not damage 12/15V converters.
However they may not meet all listed specifi cations.
Filtering and Noise Reduction
All A-Series UWR DC/DC Converters achieve their rated ripple and noise
specifi cations using the external input and output capacitors specifi ed in the
Performance/Functional Specifi cations 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 2-3 inches from the converter to achieve published ratings. The
most effective combination of external I/O capacitors will be a function of your
particular load and layout conditions.
Input Fusing
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 MPS's A-Series UWR 7-15 Watt DC/DC Converters, you
should use fast-blow type fuses with values no greater than the following.
V
IN Range Fuse Value
"D12A" Models 3 Amps
"D24A" Models 2 Amps
"D48A" Models 1 Amp
Maximum Case Temperature
The +100 degree C. maximum outside case temperature specifi cation is based
on much empirical testing on encapsulated units. Those tests show that if
the case exterior can be maintained at or below +100C., the hottest internal
components’ package temperatures will not exceed +128C. because of the
internal temperature gradient to the exterior case. This latter +128C. internal
fi gure is a safety margin offering more protection for the internal components.
The +100C. case specifi cation must be achieved by the user’s combination of
lower output current and/or higher airfl ow.
If you attempt any of your own case temperature testing, please be aware of
the heatsinking effect of attaching wired thermocouples to surfaces. An infra-
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UWR Models
Single Output,
High-Density,
6 Amp/15 Watt
DC/DC Converters
MDC_UWR_7-15.I02 Page 4 of 13
