Datasheet
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Figure 6. Measuring Output Ripple and Noise (PARD)
C1
C1 = 1µF
C2 = 10µF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
+SENSE
−SENSE
−VOUT
Input Source Impedance
These converters will operate to specifi cations without external components,
assuming that the source voltage has very low impedance and reasonable
input voltage regulation. Since real-world voltage sources have fi nite imped-
ance, performance is improved by adding external fi lter components. Some-
times only a small ceramic capacitor is suffi cient. Since it is diffi cult to totally
characterize all applications, some experimentation may be needed. Note that
external input capacitors must accept high speed switching currents.
Because of the switching nature of DC-DC converters, the input of these
converters must be driven from a source with both low AC impedance and
adequate DC input regulation. Performance will degrade with increasing input
inductance. Excessive input inductance may inhibit operation. The DC input
regulation specifi es that the input voltage, once operating, must never degrade
below the Shut-Down Threshold under all load conditions. Be sure to use
adequate trace sizes and mount components close to the converter.
I/O Filtering, Input Ripple Current and Output Noise
All models in this converter series are tested and specifi ed for input refl ected
ripple current and output noise using designated external input/output compo-
nents, circuits and layout as shown in the fi gures below. External input capaci-
tors (Cin in the fi gure) serve primarily as energy storage elements, minimizing
line voltage variations caused by transient IR drops in the input conductors.
Users should select input capacitors for bulk capacitance (at appropriate
frequencies), low ESR and high RMS ripple current ratings. In the fi gure below,
the Cbus and Lbus components simulate a typical DC voltage bus. Your specifi c
system confi guration may require additional considerations. Please note that the
values of Cin, Lbus and Cbus will vary according to the specifi c converter model.
In critical applications, output ripple and noise (also referred to as periodic
and random deviations or PARD) may be reduced by adding fi lter elements
such as multiple external capacitors. Be sure to calculate component tempera-
ture rise from refl ected AC current dissipated inside capacitor ESR.
Floating Outputs
Since these are isolated DC-DC converters, their outputs are “fl oating” with
respect to their input. The essential feature of such isolation is ideal ZERO
CURRENT FLOW between input and output. Real-world converters however do
exhibit tiny leakage currents between input and output (see Specifi cations).
These leakages consist of both an AC stray capacitance coupling component
and a DC leakage resistance. When using the isolation feature, do not allow
the isolation voltage to exceed specifi cations. Otherwise the converter may
be damaged. Designers will normally use the negative output (-Output) as
the ground return of the load circuit. You can however use the positive output
(+Output) as the ground return to effectively reverse the output polarity.
Minimum Output Loading Requirements
All models regulate within specifi cation and are stable under no load to full
load conditions. Operation under no load might however slightly increase
output ripple and noise.
Thermal Shutdown
To protect against thermal overstress, these converters include thermal
shutdown circuitry. If environmental conditions cause the temperature of the
DC-DC’s to rise above the Operating Temperature Range up to the shutdown
temperature, an on-board electronic temperature sensor will power down
the unit. When the temperature decreases below the turn-on threshold, the
converter will automatically restart. There is a small amount of hysteresis to
prevent rapid on/off cycling. The temperature sensor is typically located adja-
cent to the switching controller, approximately in the center of the unit. See the
Performance and Functional Specifi cations.
CAUTION: If you operate too close to the thermal limits, the converter may
shut down suddenly without warning. Be sure to thoroughly test your applica-
tion to avoid unplanned thermal shutdown.
Temperature Derating Curves
The graphs in this data sheet illustrate typical operation under a variety of
conditions. The Derating curves show the maximum continuous ambient air
temperature and decreasing maximum output current which is acceptable
under increasing forced airfl ow measured in Linear Feet per Minute (“LFM”).
Note that these are AVERAGE measurements. The converter will accept brief
increases in current or reduced airfl ow as long as the average is not exceeded.
Figure 5. Measuring Input Ripple Current
C
IN
V
IN
C
BUS
L
BUS
C
IN
= 33µF, ESR < 700mΩ @ 100kHz
C
BUS
= 220µF, ESR < 100mΩ @ 100kHz
L
BUS
= 12µH
+VIN
−VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
UEE 150W Series
Isolated, High-Density, Eighth-Brick
DOSA Low Profi le DC-DC Converters
MDC_UEE 150W_Series.A02 Page 31 of 35