OKI-T3-W40 Datasheet, PDF (7/12 Pages) Murata Power Solutions Inc. – Adjustable Output 3-Amp DOSA-SMT DC/DC Converters

OKI-T/3-W40 Series
Adjustable Output 3-Amp DOSA-SMT DC/DC Converters
+OUTPUT
-OUTPUT
COPPER STRIP
C1
C2
SCOPE
COPPER STRIP
CAUTION: If you routinely or accidentally exceed these Derating guidelines,
the converter may have an unplanned Over Temperature shut down. Also, these
graphs are all collected at slightly above Sea Level altitude. Be sure to reduce
the derating for higher density altitude.
Output Fusing
RLOAD _{The converter is extensively protected against current, voltage and temperature}
extremes. However your output application circuit may need additional protec-
tion. In the extremely unlikely event of output circuit failure, excessive voltage
could be applied to your circuit. Consider using an appropriate fuse in series
with the output.
C1 = 0.1μF CERAMIC
C2 = 10μF TANTALUM
LOAD 2-3 INCHES (51-76mm) FROM MODULE
Figure 3: Measuring Output Ripple and Noise (PARD)
Minimum Output Loading Requirements
All models regulate within specification 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 prevent many over temperature problems and damage, 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.
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 the next section 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 airflow measured in Linear Feet per Minute (“LFM”).
Note that these are AVERAGE measurements. The converter will accept brief
increases in current or reduced airflow as long as the average is not exceeded.
Note that the temperatures are of the ambient airflow, not the converter
itself which is obviously running at higher temperature than the outside air.
Also note that “natural convection” is defined as very flow rates which are not
using fan-forced airflow. Depending on the application, “natural convection” is
usually about 30-65 LFM but is not equal to still air (0 LFM).
Murata Power Solutions makes Characterization measurements in a closed
cycle wind tunnel with calibrated airflow. We use both thermocouples and an
infrared camera system to observe thermal performance. As a practical matter,
it is quite difficult to insert an anemometer to precisely measure airflow in
most applications. Sometimes it is possible to estimate the effective airflow if
you thoroughly understand the enclosure geometry, entry/exit orifice areas and
the fan flowrate specifications.
Output Current Limiting
Current limiting inception is defined as the point at which full power falls below
the rated tolerance. See the Performance/Functional Specifications. Note par-
ticularly that the output current may briefly rise above its rated value in normal
operation as long as the average output power is not exceeded. This enhances
reliability and continued operation of your application. If the output current is
too high, the converter will enter the short circuit condition.
Output 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 (approxi-
mately 98% of nominal output voltage for most models), 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 voltage to begin ramping up to its appropriate value.
If the short-circuit condition persists, another shutdown cycle will initiate. This
rapid on/off cycling is called “hiccup mode”. The hiccup cycling reduces the
average output current, thereby preventing excessive internal temperatures
and/or component damage. A short circuit can be tolerated indefinitely.
The “hiccup” system differs from older latching short circuit systems
because you do not have to power down the converter to make it restart. The
system will automatically restore operation as soon as the short circuit condi-
tion is removed.
Remote On/Off Control
On the input side, a remote On/Off Control can be ordered with either polarity.
Please refer to the Connection Diagram on page 1 for On/Off connections.
Positive-polarity models are enabled when the On/Off pin is left open or is
pulled high to +Vin with respect to –Vin. Positive-polarity devices are disabled
when the On/Off is grounded or brought to within a low voltage (see Specifica-
tions) with respect to –Vin.
Negative-polarity devices are on (enabled) when the On/Off is left open or
brought to within a low voltage (see Specifications) with respect to –Vin. The
device is off (disabled) when the On/Off is pulled high (see Specifications) with
respect to –Vin.
Dynamic control of the On/Off function should be able to sink appropriate
signal current when brought low and withstand appropriate voltage when
brought high. Be aware too that there is a finite time in milliseconds (see
Specifications) between the time of On/Off Control activation and stable,
regulated output. This time will vary slightly with output load type and current
and input conditions.
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05 Nov 2009 MDC_OKI-T/3-W40 Series.A01_D8 Page 7 of 12