Datasheet

UWQ-12/17-Q48T-C Series
Wide Input, Isolated DOSA Quarter Brick
DC-DC Converters with Trim and Sense
MDC_UWQ-12-17-Q48T-C.A01 Page 13 of 17
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Input Fusing
Certain applications and/or safety agencies may require fuses at the inputs of
power conversion components. Fuses should also be used when there is the
possibility of sustained input voltage reversal which is not current-limited. For
greatest safety, we recommend a fast blow fuse installed in the +Vin supply
line.
The installer must observe all relevant safety standards and regulations. For
safety agency approvals, install the converter in compliance with the end-user
safety standard.
Input Under-Voltage Shutdown and Start-Up Threshold
Under normal start-up conditions, converters will not begin to regulate
properly until the rising input voltage exceeds and remains above the Start-Up
Threshold Voltage (see Specifi cations). Once operating, converters will not
turn off until the input voltage drops below the Under-Voltage Shutdown Limit.
Subsequent restart will not occur until the input voltage rises again above the
Start-Up Threshold. This built-in hysteresis prevents any unstable on/off opera-
tion at a single input voltage.
Users should be aware however of input sources near the Under-Voltage Shut-
down whose voltage decays as input current is consumed (such as capacitor
inputs), the converter shuts off and then restarts as the external capacitor re-
charges. Such situations could oscillate. To prevent this, make sure the operating
input voltage is well above the UV Shutdown voltage AT ALL TIMES.
Start-Up Delay
Assuming that the output current is set at the rated maximum, the Vin to Vout Start-
Up Delay (see Specifi cations) is the time interval between the point when the rising
input voltage crosses the Start-Up Threshold and the fully loaded regulated output
voltage enters and remains within its specifi ed regulation band. Actual measured
times will vary with input source impedance, external input capacitance, input volt-
age slew rate and fi nal value of the input voltage as it appears at the converter.
These converters include a soft start circuit to moderate the duty cycle of the
PWM controller at power up, thereby limiting the input and output inrush current.
The On/Off Remote Control interval from inception to V
OUT regulated assumes
that the converter already has its input voltage stabilized above the Start-Up
Threshold before the On command. The interval is measured from the On com-
mand until the output enters and remains within its specifi ed regulation band.
The specifi cation assumes that the output is fully loaded at maximum rated
current.
Input Source Impedance
These converters will operate to specifi cations without external components,
assuming that the source voltage has very low impedance. Since real-world
voltage sources have fi nite minimum impedance, performance is improved
by adding external fi lter components. Sometimes only a small ceramic input
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.
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
TECHNICAL NOTES
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 (C
IN 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 fre-
quencies), low ESR and high RMS ripple current ratings. In the fi gure below, the
C
BUS and LBUS components simulate a typical DC voltage bus. Specifi c system
confi gurations may require additional considerations. Please note that the val-
ues of C
IN, LBUS and CBUS may 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 temperature rise
from refl ected AC current dissipated inside capacitor ESR. In order to minimize
circuit errors and standardize tests between units, scope measurements should
be made using BNC connectors or the probe ground should not exceed one half
inch and soldered directly to the fi xture.
C IN
V IN
C BUS
L BUS
C IN = 33µF, ESR < 200mΩ @ 100kHz
C
BUS = 220µF, 100V
L
BUS = 12µH
+VIN
−VIN
CURRENT
PROBE
TO
OSCILLOSCOPE
+
–
+
–
Figure 2. Measuring Input Ripple Current
Figure 3. Measuring Output Ripple and Noise (PARD)
C1
C1 = 1µF
C2 = 10µF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
−VOUT