UHE Datasheet, PDF (13/16 Pages) Murata Manufacturing Co., Ltd. – Isolated, High Effi ciency, 1.6" × 2" 2-10 Amp, 12-30 Watt DC/DC Converters

UHE Series
Isolated, High Efficiency, 1.6" × 2"
2-10 Amp, 12-30 Watt DC/DC Converters
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 imped-
ance can affect system stability. In Figure 2, CBUS and LBUS simulate a typical
dc voltage bus. Your specific system configuration may necessitate additional
considerations.
TO
OSCILLOSCOPE
+
VIN
–
LBUS
CBUS
CURRENT
PROBE
CIN
+INPUT
CIN = 33μF, ESR < 700m7 @ 100kHz
CBUS = 220μF, ESR < 100m7 @ 100kHz
LBUS = 12μH
–INPUT
Figure 2. Measuring Input Ripple Current
In critical applications, output ripple/noise (also referred to as periodic and
random deviations or PARD) may be reduced below specified limits using filter-
ing techniques, the simplest of which is the installation of additional external
output capacitors. These output caps function as true filter 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. Our Applications Engineers can recommend potential solutions and
discuss the possibility of our modifying a given device's internal filtering to
meet your specific requirements. Contact our Applications Engineering Group
for additional details.
+SENSE
+OUTPUT
C1
C2
SCOPE
RLOAD
–OUTPUT
–SENSE
C1 = 0.47μF
C2 = NA
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3. Measuring Output Ripple/Noise (PARD)
Floating Outputs
Since these are isolated DC/DC converters, their outputs are "floating" with
respect to their input. Designers will normally use the –Output (pin 7) as the
ground/return of the load circuit. You can, however, use the +Output (pin 6) as
ground/return to effectively reverse the output polarity.
Minimum Output Loading Requirements
UHE converters employ a synchronous-rectifier design topology and all models
regulate within spec and are stable under no-load to full load conditions.
Operation under no-load conditions however might slightly increase the output
ripple and noise.
Thermal Shutdown
These UHE converters are equipped with thermal-shutdown circuitry. If envi-
ronmental conditions cause the internal temperature of the DC/DC converter to
rise above the designed operating temperature, a precision temperature sensor
will power down the unit. When the internal temperature decreases below the
threshold of the temperature sensor, the unit will self start. See Performance/
Functional Specifications.
Output Overvoltage Protection
UHE output voltages are monitored for an overvoltage condition via magnetic
feedback. The signal is coupled to the primary side and if the output voltage
rises to a level which could be damaging to the load, the sensing circuitry will
power down the PWM controller causing the output voltages to decrease. Fol-
lowing a time-out period the PWM will restart, causing the output voltages to
ramp to their appropriate values. If the fault condition persists, and the output
voltages again climb to excessive levels, the overvoltage circuitry will initiate
another shutdown cycle. This on/off cycling is referred to as "hiccup" mode.
Contact MPS for an optional output overvoltage monitor circuit using a
comparator which is optically coupled to the primary side thus allowing tighter
and more precise control.
Current Limiting (Power limit with current mode control)
As power demand increases on the output and enters the specified “limit
inception range” (current in voltage mode and power in current mode) limiting
circuitry activates in the DC-DC converter to limit/restrict the maximum current
or total power available. In voltage mode, current limit can have a “constant or
foldback” characteristic. In current mode, once the current reaches a certain
range the output voltage will start to decrease while the output current con-
tinues to increase, thereby maintaining constant power, until a maximum peak
current is reached and the converter enters a “hiccup” (on off cycling) mode of
operation until the load is reduced below the threshold level, whereupon it will
return to a normal mode of operation. Current limit inception is defined as the
point where the output voltage has decreased by a pre-specified percentage
(usually a 2% decrease from nominal).
Short Circuit Condition (Current mode control)
The short circuit condition is an extension of the “Current Limiting” condition.
When the monitored peak current signal reaches a certain range, the PWM
controller’s outputs are shut off thereby turning the converter “off.” This is
followed by an extended time out period. This period can vary depending on
other conditions such as the input voltage level. Following this time out period,
the PWM controller will attempt to re-start the converter by initiating a “normal
start cycle” which includes softstart. If the “fault condition” persists, another
“hiccup” cycle is initiated. This “cycle” can and will continue indefinitely until
such time as the “fault condition” is removed, at which time the converter will
resume “normal operation.” Operating in the “hiccup” mode during a fault
condition is advantageous in that average input and output power levels are
held low preventing excessive internal increases in temperature.
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MDC_UHE_12-30W Series.C01 Page 13 of 16