Datasheet

UWE Series
Wide Input, Isolated
Eighth-Brick DC-DC Converters
MDC_UWE Series.E04 Page 20 of 23
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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
magnetically 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 voltages to begin ramping to their
appropriate values. 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 UWE is capable of enduring
an indefi nite short circuit output condition.
Features and Options
On/Off Control
The input-side, remote On/Off Control function can be ordered to operate with
either logic type:
Positive-logic models (“P" part-number suffi x) are enabled when the On/Off
Control is left open or is pulled high, as per Figure 4. Positive-logic devices are
disabled when the On/Off Control is pulled low.
Negative-logic devices (“N” suffi x) are off when the On/Off Control is open (or
pulled high), and on when the On/Off Control is pulled low with respect to –V
IN
as shown in Figure 5.
Floating Outputs
Since these are isolated DC-DC converters, their outputs are "fl oating" with
respect to their input. Designers will normally use the –Output as the ground/
return of the load circuit. You can, however, use the +Output as ground/return
to effectively reverse the output polarity.
Minimum Output Loading Requirements
UWE converters employ a synchronous-rectifi er 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 UWE 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 Specifi cations.
Output Overvoltage Protection
UWE 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.
Current Limiting
As soon as the output current increases to substantially above its rated value,
the DC-DC converter will go into a current-limiting mode. In this condition, 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 defi ned as the point at
which the full-power output voltage falls below the specifi ed tolerance. See
Performance/Functional Specifi cations. If the load current, being drawn from
the converter, is signifi cant enough, the unit will go into a short circuit condition
as specifi ed under "Performance."
C1
C1 = 0.47μF CERAMIC
C2 = NA
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
–VOUT
+SENSE
–SENSE
Figure 3. Measuring Output Ripple/Noise (PARD)
ON/OFF CONTROL
CONTROL
+ Vcc
-VIN
Figure 4. Driving the Positive Logic On/Off Control Pin
–VIN
O N /O F F
C O N TR O L
+ Vcc
Figure 5. Driving the Negative Logic On/Off Control Pin