Datasheet

UWE Series
Wide Input, Isolated
Eighth-Brick DC-DC Converters
MDC_UWE Series.E04 Page 19 of 23
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TECHNICAL NOTES
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 exist. For MPS UWE DC-DC Converters, you should use fast-blow type
fuses, installed in the ungrounded input supply line. Refer to the specifi cations
for fuse values.
All relevant national and international safety standards and regulations must
be observed by the installer. For system safety agency approvals, the convert-
ers must be installed in compliance with the requirements of the end-use
safety standard, e.g., IEC/EN/UL60950-1.
Input Undervoltage Shutdown and Start-Up Threshold
Under normal start-up conditions, devices will not begin to regulate until
the ramping-up input voltage exceeds the Start-Up Threshold Voltage. Once
operating, devices will not turn off until the input voltage drops below the
Undervoltage Shutdown limit. Subsequent re-start will not occur until the input
is brought back up to the Start-Up Threshold. This built in hysteresis prevents
any unstable on/off situations from occurring at a single input voltage.
Start-Up Time
The VIN to VOUT Start-Up Time is the interval of time between the point at which
the ramping input voltage crosses the Start-Up Threshold and the fully loaded
output voltage enters and remains within its specifi ed accuracy band. Actual
measured times will vary with input source impedance, external input/output
capacitance, and load. The UWE Series implements a soft start circuit that
limits the duty cycle of its PWM controller at power up, thereby limiting the
input inrush current.
The On/Off Control to V
OUT start-up time assumes the converter has its
nominal input voltage applied but is turned off via the On/Off Control pin. The
specifi cation defi nes the interval between the point at which the converter is
turned on and the fully loaded output voltage enters and remains within its
specifi ed accuracy band. Similar to the V
IN to VOUT start-up, the On/Off Control
to V
OUT start-up time is also governed by the internal soft start circuitry and
external load capacitance.
The difference in start up time from V
IN to VOUT and from On/Off Control to
V
OUT is therefore insignifi cant.
Input Source Impedance
UWE converters must be driven from a low ac-impedance input source.
The DC-DC’s performance and stability can be compromised by the use of
highly inductive source impedances. For optimum performance, compo-
nents should be mounted close to the DC-DC converter. If the application
has a high source impedance, low V
IN models can benefit from increased
external input capacitance.
I/O Filtering, Input Ripple Current, and Output Noise
All models in the UWE Converters are tested/specifi ed for input refl ected ripple
current and output noise using the specifi ed external input/output components/
circuits and layout as shown in the following two fi gures.
External input capacitors (C
IN in Figure 2) serve primarily as energy-storage
elements, minimizing line voltage variations caused by transient IR drops in
conductors from backplane to the DC-DC. Input caps should be selected for bulk
capacitance (at appropriate frequencies), low ESR, and high rms-ripple-current
ratings. The switching nature of DC-DC converters requires that dc voltage
sources have low ac impedance as highly inductive source impedance can affect
system stability. In Figure 2, C
BUS and LBUS simulate a typical dc voltage bus. Your
specifi c system confi guration may necessitate additional considerations.
CINVIN CBUS
LBUS
CIN = 33µF, ESR < 700mΩ @ 100kHz
C
BUS = 220µF, ESR < 100mΩ @ 100kHz
L
BUS = 12µH
+VIN
–VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
Figure 2. Measuring Input Ripple Current
Soldering Guidelines
Murata Power Solutions recommends the specifi cations below when installing these
converters. These specifi cations vary depending on the solder type. Exceeding these
specifi cations may cause damage to the product. Your production environment may dif-
fer; therefore please thoroughly review these guidelines with your process engineers.
Wave Solder Operations for through-hole mounted products (THMT)
For Sn/Ag/Cu based solders:
Maximum Preheat Temperature 115° C.
Maximum Pot Temperature 270° C.
Maximum Solder Dwell Time 7 seconds
For Sn/Pb based solders:
Maximum Preheat Temperature 105° C.
Maximum Pot Temperature 250° C.
Maximum Solder Dwell Time 6 seconds
In critical applications, output ripple/noise (also referred to as periodic and
random deviations or PARD) may be reduced below specifi ed limits using fi lter-
ing techniques, the simplest of which is the installation of additional external
output capacitors. These output caps function as true fi lter elements and
should be selected for bulk capacitance, low ESR and appropriate frequency
response. All external capacitors should have appropriate voltage ratings and
be located as close to the converter as possible. Temperature variations for all
relevant parameters should also be taken carefully into consideration.
The most effective combination of external I/O capacitors will be a function
of line voltage and source impedance, as well as particular load and layout
conditions.