Datasheet

EMH-54/3-Q48N-C Series
Isolated, 54Vout, 3A, Ethernet Power
Half-Brick DC/DC Converters
MDC_EMH-54/3-Q48N-C.A05 Page 13 of 15
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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. The temperature sensor is typically
located adjacent to the switching controller, approximately in the center of the
unit. See the Performance and Functional Specifi cations.
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 temperature and/or current or reduced airfl ow as long as the aver-
age 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 very low fl ow rates are similar to “natural convection,” that is, not
using fan-forced airfl ow.
Murata Power Solutions makes characterization measurements in a closed
loop wind tunnel with measured airfl ow. We use both thermocouples and an
infrared camera system to observe thermal performance. If in doubt, contact
Murata Power Solutions to discuss placement and measurement techniques of
suggested temperature sensors.
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 Overvoltage Protection
This converter monitors its output voltage for an over-voltage condition using
an on-board electronic comparator. If the output exceeds OVP limits, the
sensing circuit will power down the unit, and the output voltage will decrease.
After a time-out period, the PWM will automatically attempt to restart, causing
the output voltage to ramp up to its rated value. It is not necessary to power
down and reset the converter for this automatic OVP-recovery restart.
If the fault condition persists and the output voltage climbs to excessive
levels, the OVP circuitry will initiate another shutdown cycle. This on/off cycling
is referred to as “hiccup” mode.
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
As soon as the output current increases to its maximum rated value, the DC/DC
converter will enter a power-limiting mode. The output voltage will decrease
proportionally with increases in output current, thereby maintaining a some-
what constant power output. This is commonly referred to as power 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
particularly that the output current may briefl y rise above its rated value. 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 power-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 up to its appro-
priate value. If the short-circuit condition persists, another shutdown cycle will
initiate. This on/off cycling is called “hiccup mode”. The hiccup cycling reduces
the average output current, thereby preventing excessive internal tempera-
tures. A short circuit can be tolerated indefi nitely.
Remote On/Off Control
Negative: Optional negative-logic devices are on (enabled) when the On/Off is
grounded 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 to +Vin 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 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.
There are two CAUTIONs for the On/Off Control:
CAUTION: While it is possible to control the On/Off with external logic if you
carefully observe the voltage levels, the preferred circuit is either an open
drain/open collector transistor or a relay (which can thereupon be controlled by
logic).
CAUTION: Do not apply voltages to the On/Off pin when there is no input
voltage. Otherwise the converter may be permanently damaged.
Figure 2. Measuring Output Ripple and Noise (PARD)
C1
C1 = 1µF CERAMIC
LOAD 2-3 INCHES (51-76mm) FROM MODULE
R
LOAD
5
SCOPE
+OUTPUT
9
-OUTPUT