UWS Datasheet, PDF (23/25 Pages) Murata Power Solutions Inc. – Sixteenth-brick DOSA-Compatible, Wide Input Isolated DC/DC

UWS Series
+SENSE
+OUTPUT
C1
C2
SCOPE
RLOAD
–OUTPUT
–SENSE
C1 = 1μF
C2 = 10μF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3. Measuring Output Ripple/Noise (PARD)
Thermal Shutdown
The UWS converters are equipped with thermal-shutdown circuitry. If environ-
mental conditions cause the 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 Over-Voltage Protection
The UWS output voltage is monitored for an over-voltage condition using a com-
parator. The signal is optically coupled to the primary side and if the output volt-
age rises to a level which could be damaging to the load, the sensing circuitry
will power down the PWM controller causing the output voltage to decrease.
Following a time-out period the PWM will restart, causing the output voltage
to ramp to its appropriate value. If the fault condition persists, and the output
voltage again climbs to excessive levels, the over-voltage circuitry will initiate
another shutdown cycle. This on/off cycling is referred to as “hiccup” mode.
Current Limiting
As soon as the output current increases to approximately 130% of its rated
value, the DC/DC converter will go into a current-limiting mode. In this condi-
tion, the output voltage will decrease proportionately with increases in output
current, thereby maintaining somewhat constant power dissipation. This is
commonly referred to as power limiting. Current limit inception is defined
as the point at which the full-power output voltage falls below the specified
tolerance. See Performance/Functional Specifications. If the load current, being
drawn from the converter, is significant enough, the unit will go into a short
circuit condition as described below.
Short Circuit Condition
When a converter is in current-limit mode, the output voltage will drop as the
output current demand increases. If the output voltage drops too low, the mag-
netically coupled voltage used to develop primary side voltages will also drop,
thereby shutting down the PWM controller. Following a time-out period, the
PWM will restart causing the output voltage to begin ramping to their appropri-
ate value. If the short-circuit condition persists, another shutdown cycle will be
initiated. This on/off cycling is referred to as “hiccup” mode. The hiccup cycling
reduces the average output current, thereby preventing internal temperatures
from rising to excessive levels. The UWS Series is capable of enduring an
indefinite short circuit output condition.
Sixteenth-brick DOSA-Compatible,
Wide Input Isolated DC/DC Converters
Remote Sense (models UWS-3.3/15-Q48 and UWS-5/10-Q48 only)
Note: The Sense and VOUT lines are internally connected through low-value
resistors. Nevertheless, if the sense function is not used for remote regulation
the user should connect the +Sense to +VOUT and –Sense to –VOUT at the DC/
DC converter pins. ULS series converters employ a sense feature to provide
point of use regulation, thereby overcoming moderate IR drops in PCB conduc-
tors or cabling. The remote sense lines carry very little current and therefore
require minimal cross-sectional-area conductors. The sense lines, which are
capacitively coupled to their respective output lines, are used by the feedback
control-loop to regulate the output. As such, they are not low impedance points
and must be treated with care in layouts and cabling. Sense lines on a PCB
should be run adjacent to dc signals, preferably ground.
[VOUT(+)-VOUT(–)] – [Sense(+)-Sense(–)] d 10%VOUT
In cables and discrete wiring applications, twisted pair or other techniques
should be used. Output over-voltage protection is monitored at the output volt-
age pin, not the Sense pin. Therefore, excessive voltage differences between
VOUT and Sense in conjunction with trim adjustment of the output voltage can
cause the over-voltage protection circuitry to activate (see Performance Speci-
fications for over-voltage limits). Power derating is based on maximum output
current and voltage at the converter’s output pins. Use of trim and sense func-
tions can cause output voltages to increase, thereby increasing output power
beyond the converter’s specified rating, or cause output voltages to climb into
the output over-voltage region. Therefore, the designer must ensure:
(VOUT at pins) x (IOUT) d rated output power
Contact and PCB resistance
losses due to IR drops
–INPUT
ON/OFF
CONTROL
+INPUT
+OUTPUT
+SENSE
TRIM
–SENSE
–OUTPUT
IOUT
Sense Current
Sense Return
LOAD
IOUT Return
Contact and PCB resistance
losses due to IR drops
Figure 4. Remote Sense Circuit Configuration
Sense is included only on models UWS-3.3/15-Q48 and UWS-5/10-Q48.
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MDC_UWS Series.B02 Page 23 of 25