MYSGK02506BRSR
DC-DC converter
TECHNICAL NOTES
Input Fusing
Recommended Output Filtering
Certain applications and/or safety agencies may require fuses at the inputs
of power conversion components.
Fuses should also be used when there is the possibility of sustained input
voltage reversal which is not current limited.
For greatest safety, we recommend a fast blow fuse installed in the
ungrounded input supply line. The installer must observe all relevant safety
standards and regulations. For safety agency approvals, install the converter
in compliance with the end-user safety standard.
The converter will achieve its rated output ripple and noise with additional
external capacitor. The user may install more external output
capacitance reduce the ripple even further or for improved dynamic response.
Initial suggested capacitor values are 4.7uF ceramic type and 68uF
Conductive Polymer Hybrid Aluminum Electrolytic Capacitor.
Measure the output ripple under your load conditions.
Use only as much capacitance as required to achieve your ripple and noise
objectives. Excessive capacitance can make step load recovery sluggish or
possibly introduce instability. Do not exceed the maximum rated output
capacitance listed in the specifications.
Input Under-Voltage Shutdown and Startup Threshold
RUVLO1 and RUVLO2 can be used to set the Shutdown and Startup
Threshold.
Output Noise
Under normal Startup conditions, converter will not begin to regulate properly
until the ramping-up input voltage exceeds and remains at the Startup
Threshold Voltage.
All models in this converter series are tested and specified for output noise
using designated external input/output components, circuits and layout as
shown in the figures below.
Once operating, converter will not turn off until the input voltage drops below
the Under-Voltage Shutdown Limit. Subsequent restart will not occur until
the input voltage rises again above the Startup Threshold. This built-in
hysteresis prevents any unstable on/off operation at a single input voltage.
Users should be aware however of input sources near the Under-Voltage
Shutdown whose voltage decays as input current is consumed (such as
capacitor inputs), the converter shutdown and then restarts as the external
capacitor recharges. Such situations could oscillate. To prevent this, make
sure the operating input voltage is well above the Under-Voltage Shutdown
voltage at all times.
In the figure below, the two copper strips simulate real-world printed circuit
impedances between the power supply and its load. In order to minimize
circuit errors and standardize tests between units, scope measurements
should be made using BNC connectors or the probe ground should not
exceed one half inch and soldered directly to the test circuit.
Start-Up Time
Assuming that the output current is set at the rated maximum, the Vin to Vo
Startup Time (see Specifications) is the time interval between the point when
the ramping input voltage crosses the Startup Threshold and the fully loaded
regulated output voltage enters and remains within its specified accuracy
band. Actual measured times will vary with input source impedance, external
input capacitance, input voltage slew rate and final value of the input voltage
as it appears at the converter.
The converter include a soft start circuit to moderate the duty cycle of
its PWM controller at power up, thereby limiting the input inrush current.
The On/Off Remote Control interval from On command to Vo regulated
assumes that the converter already has its input voltage stabilized above the
Startup Threshold before the On command. The interval is measured from
the On command until the output enters and remains within its specified
accuracy band. The specification assumes that the output is fully loaded at
maximum rated current. Similar conditions apply to the On to Vo regulated
specification such as external load capacitance and soft start circuitry.
C1=4.7uF (Ceramic Capacitor))
C2=68uF (Conductive Polymer Hybrid Aluminum Electrolytic Capacitor)
Figure: Measuring Output Ripple and Noise
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. Note that these are AVERAGE measurements. 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
very low flow rates (below about 25 LFM) are similar to “natural convection,”
that is, not using fan-forced airflow. Murata 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.
Recommended Input Filtering
The user must assure that the input source has low AC impedance to
provide dynamic stability and that the input supply has little or no inductive
content, including long distributed wiring to a remote power supply. The
converter will operate with no additional external capacitance if these
conditions are met. For best performance, we recommend installing a low-
ESR capacitor immediately adjacent to the converter’s input terminals.
The capacitor should be a ceramic type such as the Murata GRM32 series or
GRM31 series and a electrolytic type such as Panasonic OS-CON series.
Initial suggested capacitor values are 4.7uF*4 ceramic type and 1000uF*1
electrolytic type , rated at twice the expected maximum input voltage. Make
sure that the input terminals do not go below the under voltage shutdown
voltage at all times. More input bulk capacitance may be added in parallel
(either electrolytic or tantalum) if needed.
CAUTION: These graphs are all collected at slightly above Sea Level
altitude. Be sure to reduce the derating for higher density altitude.
Output Short Circuit Protection
In the case of a heavy overload setting such as a short circuit, the converter
temporarily stop output.
Following a time-out period, the converter 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 condition is
removed.
http://www.murata.com/products/power
MYSGK02506BRSR A04 Page 17 of 18
