age’ & ‘Isolation Test Voltage’ are all terms that relate to the same thing, a test voltage,
applied for a specified time, across a component designed to provide electrical isolation,
to verify the integrity of that isolation.
Murata Power Solutions MTU1 series of DC/DC converters are all 100% production tested
at their stated isolation voltage. This is 1kVDC for 1 second.
A question commonly asked is, “What is the continuous voltage that can be applied
across the part in normal operation?”
The MTU1 has been recognized by Underwriters Laboratory for functional insulation, both
input and output should normally be maintained within SELV limits i.e. less than 42.4V
peak, or 60VDC. The isolation test voltage represents a measure of immunity to transient
voltages and the part should never be used as an element of a safety isolation system.
The part could be expected to function correctly with several hundred volts offset applied
continuously across the isolation barrier; but then the circuitry on both sides of the bar-
rier must be regarded as operating at an unsafe voltage and further isolation/insulation
systems must form a barrier between these circuits and any user-accessible circuitry
according to safety standard requirements.
REPEATED HIGH-VOLTAGE ISOLATION TESTING
It is well known that repeated high-voltage isolation testing of a barrier component can
actually degrade isolation capability, to a lesser or greater degree depending on materi-
als, construction and environment. The MTU1 series has toroidal isolation transformers,
with no additional insulation between primary and secondary windings of enameled
wire. While parts can be expected to withstand several times the stated test voltage,
the isolation capability does depend on the wire insulation. Any material, including this
enamel (typically polyurethane) is susceptible to eventual chemical degradation when
subject to very high applied voltages thus implying that the number of tests should be
strictly limited. We therefore strongly advise against repeated high voltage isolation test-
ing, but if it is absolutely required, that the voltage be reduced by 20% from specified
test voltage.
This consideration equally applies to agency recognized parts rated for better than func-
tional isolation where the wire enamel insulation is always supplemented by a further
insulation system of physical spacing or barriers.
SAFETY APPROVAL
The MTU1 series has been recognized by Underwriters Laboratory (UL) to UL 60950 for functional insulation to a maximum product PCB temperature of 120°C. Forced air cooling
may be used to maintain this temperature requirement. File number E151252 applies.
The MTU1 Series of converters are not internally fused so to meet the requirements of UL 60950 an anti-surge input line fuse should always be used with ratings as defined below.
MTU1X03xxxC: 0.750A
MTU1X05xxxC: 0.125A
MTU1X12xxxC: 0.315A
All fuses should be UL approved and rated to at least the maximum allowable DC input voltage.
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KDC_MTU.C02
Page 2 of 8
MTU1 Series
Isolated 1W Single & Dual Output SM DC/DC Converters
TEMPERATURE DERATING GRAPH
RoHS COMPLIANCE INFORMATION
1.5
Output Power (W)
1.0
0.5
0
-40
85°C
This series is compatible with RoHS soldering systems with a peak reflow
solder temperature of 245ºC as per J-STD-020D.1.
The pin termination finish on this product series is Matte Tin over Nickel
Preplate. The series is backward compatible with Sn/Pb soldering systems.
The series has a Moisture Sensitivity Level (MSL) 1.
Samples of the product series were tested in accordance with the condition-
ing described for MSL level 1 in IPS/J-STD-020D.1.
The product series passed electrical tests and visual inspection criteria.
For further information, please visit: www.murata-ps.com/rohs
Safe Operating Area
100
50
0
Ambient Temperature (°C)
150
TOLERANCE ENVELOPES
3.3V Input Types
9%
Single 5V output types (except 3.3V input)
6%
Output Voltage
Output Voltage
4%
1%
0%
-4%
100
1.5%
V
NOM
0%
10
25
50
75
10
25
50
75
-4%
100
Output Load Current (%)
Output Load Current (%)
Dual 5V Output types (except 3.3V input)
7%
Output Voltage
All other types
5%
Output Voltage
2%
1%
0%
-4%
100
V
NOM
1%
0%
10
25
50
75
Output Load Current (%)
10
25
50
75
-4%
100
Output Load Current (%)
The voltage tolerance envelope shows typical load regulation characteristics for this product series. The tolerance envelope is the maximum output voltage variation due to
changes in output loading and set point accuracy.
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KDC_MTU.C02
Page 3 of 8
MTU1 Series
Isolated 1W Single & Dual Output SM DC/DC Converters
APPLICATION NOTES
Minimum load
The minimum load to meet datasheet specification is 10% of the full rated load across the specified input voltage range. Lower than 10% minimum loading will result in
an increase in output voltage, which may rise to typically double the specified output voltage if the output load falls to less than 5%.
Capacitive loading and start up
Typical start up times for this series, with a typical input voltage rise time of 2.2μs and output capacitance of 10μF, are shown in the table below. The product
series will start into a capacitance of 47μF with an increased start time, however, the maximum recommended output capacitance is 10μF.
Start-up time
ms
1.7
0.9
2.7
4.3
7.5
0.9
1.9
3.3
4.7
Start-up time
ms
3.1
1.8
5.7
10.1
19.1
1.5
4
7.5
12.5
Typical Start-Up Wave Form
MTU1S0305MC
MTU1S0505MC
MTU1S0509MC
MTU1S0512MC
MTU1S0515MC
MTU1S1205MC
MTU1S1209MC
MTU1S1212MC
MTU1S1215MC
MTU1D0305MC
MTU1D0505MC
MTU1D0509MC
MTU1D0512MC
MTU1D0515MC
MTU1D1205MC
MTU1D1209MC
MTU1D1212MC
MTU1D1215MC
Ripple & Noise Characterisation Method
Ripple and noise measurements are performed with the following test configuration.
1μF X7R multilayer ceramic capacitor, voltage rating to be a minimum of 3 times the output voltage of the DC/DC converter
10μF tantalum capacitor, voltage rating to be a minimum of 1.5 times the output voltage of the DC/DC converter with an ESR of less
C2
than 100mΩ at 100 kHz
C3
100nF multilayer ceramic capacitor, general purpose
R1
450Ω resistor, carbon film, ±1% tolerance
R2
50Ω BNC termination
T1
3T of the coax cable through a ferrite toroid
RLOAD
Resistive load to the maximum power rating of the DC/DC converter. Connections should be made via twisted wires
Measured values are multiplied by 10 to obtain the specified values.
C1
Differential Mode Noise Test Schematic
DC/DC Converter
OSCILLOSCOPE
C1 C2 C3
+
SUPPLY
Input
R1
T1
R2
Y INPUT
+
Output
-
-
R LOAD
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KDC_MTU.C02
Page 4 of 8
MTU1 Series
Isolated 1W Single & Dual Output SM DC/DC Converters
APPLICATION NOTES CONTINUED
Output Ripple Reduction
By using the values of inductance and capacitance stated, the output ripple at the
rated load is lowered to 5mV p-p max.
Component selection
Capacitor: It is required that the ESR (Equivalent Series Resistance) should be
as low as possible, ceramic types are recommended. The voltage rating should
be at least twice (except for 15V output), the rated output voltage of the DC/DC
converter.
Inductor: The rated current of the inductor should not be less than that of the
output of the DC/DC converter. At the rated current, the DC resistance of the
inductor should be such that the voltage drop across the inductor is <2% of the
rated voltage of the DC/DC converter. The SRF (Self Resonant Frequency) should
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