Datasheet

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 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.
Note that the temperatures are of the ambient airfl ow, not the converter
itself which is obviously running at higher temperature than the outside air.
Also note that “natural convection” is defi ned as very fl ow rates which are not
using fan-forced airfl ow. 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 airfl ow. We use both thermocouples and an
infrared camera system to observe thermal performance. As a practical matter,
it is quite diffi cult to insert an anemometer to precisely measure airfl ow in
most applications. Sometimes it is possible to estimate the effective airfl ow if
you thoroughly understand the enclosure geometry, entry/exit orifi ce areas and
the fan fl owrate specifi cations.
CAUTION: If you exceed these Derating guidelines, the converter may have
an unplanned Over Temperature shut down. Also, these graphs are all collected
near Sea Level altitude. Be sure to reduce the derating for higher altitude.
Output Fusing
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.
Output Current Limiting
Current limiting inception is defi ned as the point at which full power falls below
the rated tolerance. See the Performance/Functional Specifi cations. Note par-
ticularly that the output current may briefl y 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 PWM bias voltage
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 inter-
nal temperatures and/or component damage. A short circuit can be tolerated
indefi nitely.
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 Specifi ca-
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 Specifi cations) with respect to –Vin. The
device is off (disabled) when the On/Off is pulled high (see Specifi cations) with
respect to –Vin.
Dynamic control of the On/Off function should be able to sink the speci-
fi ed signal current when brought low and withstand the specifi ed voltage
when brought high. Be aware too that there is a fi nite time in milliseconds
(see Specifi cations) 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.
Output Capacitive Load
These converters do not require external capacitance added to achieve
rated specifi cations. Users should only consider adding capacitance to reduce
switching noise and/or to handle spike current load steps. Install only enough
capacitance to achieve noise objectives. Excess external capacitance may
cause regulation problems, degraded transient response and possible oscilla-
tion or instability.
C1
C1 = 1µF
C2 = 10µF
LOAD 2-3 INCHES (51-76mm) FROM MODULE
C2
R
LOAD
SCOPE
+VOUT
-VOUT
Figure 3. Measuring Output Ripple and Noise (PARD)
MDC_OKI-T/36W-W40.B01 Page 7 of 11
OKI-T/36W-W40 Series
Selectable Output 36-Watt DOSA-SMT DC-DC Converters
www.murata-ps.com/support