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RBC-12-D48PB-C Datasheet(PDF) 9 Page - Murata Power Solutions Inc. |
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RBC-12-D48PB-C Datasheet(HTML) 9 Page - Murata Power Solutions Inc. |
9 / 10 page Technical Notes I/O Filtering and Noise Reduction The RBC is tested and specified with external output capacitors. These capacitors are necessary to accommodate our test equipment and may not be required to achieve desired performance in your application. The RBC is designed with high-quality, high-performance internal I/O caps, and will oper- ate within spec in most applications with no additional external components. In particular, the RBC input capacitors are specified for low ESR and are fully rated to handle the units' input ripple currents. Similarly, the internal output capacitors are specified for low ESR and full-range frequency response. In critical applications, input/output ripple/noise may be further reduced using filtering techniques, the simplest being the installation of external I/O caps. External input capacitors serve primarily as energy-storage devices. They minimize high-frequency variations in input voltage (usually caused by IR drops in conductors leading to the DC/DC) as the switching converter draws pulses of current. Input capacitors should be selected for bulk capacitance (at appropriate frequencies), low ESR, and high rms-ripple-current ratings. The switching nature of modern DC/DC's requires that the dc input voltage source have low ac impedance at the frequencies of interest. Highly inductive source impedances can greatly affect system stability. Your specific system configuration may necessitate additional considerations. Input Fusing Most applications and or safety agencies require the installation of fuses at the inputs of power conversion components. The RBC Series may have an optional input fuse. Therefore, if input fusing is mandatory, either a normal- blow or a fast-blow fuse with a value no greater than twice the maximum input current should be installed within the ungrounded input path to the converter. Input Overvoltage and Reverse-Polarity Protection The RBC does not incorporate input reverse-polarity protection. Input voltages in excess of the specified absolute maximum ratings and input polarity rever- sals of longer than "instantaneous" duration can cause permanent damage to these devices. Start-Up Time The VIN to VOUT Start-Up Time is the interval between the time at which a rising input voltage crosses the lower limit of the specified input voltage range CIN VIN CBUS LBUS CIN = 33μF, ESR < 700m @ 100kHz CBUS = 220μF, ESR < 100m @ 100kHz LBUS = 12μH +INPUT COMMON CURRENT PROBE TO OSCILLOSCOPE + – Figure 2. Measuring Input Ripple Current and the fully loaded output voltage enters and remains within its specified regulation band. Actual measured times will vary with input source imped- ance, external input capacitance, and the slew rate and final value of the input voltage as it appears to the converter. The On/Off to VOUT Start-Up Time assumes the converter is turned off via the On/Off Control with the nominal input voltage already applied to the converter. The specification defines the interval between the time at which the converter is turned on and the fully loaded output voltage enters and remains within its specified regulation band. Thermal Considerations and Thermal Protection The typical output-current thermal-derating curves shown below enable designers to determine how much current they can reliably derive from each model of the RBC under known ambient-temperature and air-flow conditions. Similarly, the curves indicate how much air flow is required to reliably deliver a specific output current at known temperatures. The highest temperatures in RBC's occur at their output inductor, whose heat is generated primarily by I2R losses. The derating curves were developed using thermocouples to monitor the inductor temperature and varying the load to keep that temperature below +110°C under the assorted conditions of air flow and air temperature. Once the temperature exceeds +125°C (approx.), the thermal protection will disable the converter using the hiccup shutdown mode. Undervoltage Shutdown When the input voltage falls below the undervoltage threshold, the converter will terminate its output. However, this is not a latching shutdown mode. As soon as the input voltage rises above the Start-Up Threshold, the converter will restore normal operation. This small amount of hysteresis prevents most uncommanded power cycling. Since some input sources with higher output impedance will increase their output voltage greater than this hysteresis as soon as the load is removed, it is possible for this undervoltage shutdown to cycle indefinitely. To prevent this, be sure that the input supply always has adequate voltage at full load. Thermal Shutdown Extended operation at excessive temperature will initiate overtemperature shutdown triggered by a temperature sensor inside the PWM controller. This operates similarly to overcurrent and short circuit mode. The inception point of the overtemperature condition depends on the average power delivered, the ambient temperature and the extent of forced cooling airflow. Remote On/Off Control The RBC may be turned off or on using the external remote on/off control. This terminal consists of a digital input to the internal PWM controller through a protective resistor and diode. The on/off input circuit should be CMOS logic referred to the –Input power terminal however TTL or TTL-LS logic will also work or a switch to ground. If preferred, you can even run this using a bipolar transistor in “open collector” configuration or an “open drain” FET transistor. You may also leave this input unconnected and the converter will run whenever input power is applied. RBC-12/17-D48 Series Quarter Brick, Regulated Bus Converters MDC_RBC-12/17-D48.B02 Page 9 of 10 www.murata-ps.com/support |
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