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5962-9763401HXC Datasheet(PDF) 7 Page - Analog Devices |
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5962-9763401HXC Datasheet(HTML) 7 Page - Analog Devices |
7 / 20 page ADDC02808PB REV. A –7– BASIC OPERATION The ADDC02808PB converter uses a flyback topology with dual interleaved power trains operating 180 ° out of phase. Each power train switches at a fixed frequency of 500 kHz, resulting in a 1 MHz fixed switching frequency as seen at the input and output of the converter. In a flyback topology, energy is stored in the inductor during one half portion of the switching cycle and is then transferred to the output filter during the next half portion. With two interleaved power trains, energy is transferred to the output filter during both halves of the switching cycle, resulting in smaller filters to meet the required ripple. A five pole differential input EMI filter, along with a common- mode EMI capacitor and careful attention to layout parasitics, is designed to meet all applicable requirements in MIL-STD-461D when installed in a typical system setup. Due to the higher output level in this product compared to the 100 W continuous output products, input stability is more of a concern. As a result, the two inductors in the internal input EMI filter have smaller values of inductance to mitigate input stability concerns. The effectiveness of the internal input EMI filter is, therefore, slightly diminished compared to these other products. A more detailed discussion of CE102 and other EMI issues is included in the section entitled “EMI Considerations.” The maximum available peak power out is 200 W and is based on a combination of maximum junction temperatures, maximum pulsewidth, and maximum duty cycle. Refer to section entitled, “Pulsed Output Power vs. Pulse Length,” for peak power derat- ing curves for varying conditions. The unit is compensated for ultrafast transient response with minimum output voltage deviation. The compensation has been optimized and output stability insured for an external load capacitance in the range of 500 µF, 20 mΩ ESR to 4,000 µF, 2.5 m Ω ESR. Peak performance and output stability are depen- dent on minimizing parasitic inductance and resistance in the con- nection from the converter to the load. The converter uses current mode control and employs a high performance opto-isolator in its feedback path to maintain isola- tion between input and output. The control circuit is designed to give a nearly constant output current as the output voltage drops from VO nom to VSC during a short circuit condition. It does not let the current fold back below the maximum rated output current. The output overvoltage protection circuitry, which is independent from the normal feedback loop, protects the load against a break in the remote sense leads. Remote sense connections, which can be made at the load, can adjust for voltage drops of as much as 0.25 V dc between the converter and the load, thereby maintaining an accurate voltage level at the load. An input overvoltage protection feature shuts down the con- verter when the input voltage exceeds (nominally) 52.5 V dc. An internal temperature sensor shuts down the unit and pre- vents it from becoming too hot if the heat removal system fails. The temperature sensed is the case temperature and is factory set to trip at a nominal case temperature of 110 °C to 115°C. The shut down temperature setting can be raised externally or disabled by the user. Each unit has an INHIBIT pin that can be used to turn off the converter. This feature can be used to sequence the turn-on of multiple converters and to reduce input power draw during extended time in a no load condition. A SYNC pin, referenced to the input return line (Pin 10), is available to synchronize multiple units to one switching fre- quency. This feature is particularly useful in eliminating beat frequencies which may cause increased output ripple on paral- leled units. A current share pin (ISHARE) is available which permits paralleled units to share current typically within 5% at full load. A low level dc auxiliary voltage supply referenced to the input return line is provided for miscellaneous system use. PULSED OUTPUT POWER VS. PULSE LENGTH The maximum specified pulsed output power in the standard configuration of the ADDC02808PB is 200 W. This limit is based on issues of working down to the minimum input volt- age, of providing a reasonable short circuit current limit, and so on. However, this power level assumes that the junction tem- peratures of the converter’s power semiconductor devices have not exceeded 110 °C. For short pulse lengths and low duty cycles, this condition will be met. Otherwise, the pulsed output power will have to be reduced to keep the junction tempera- tures below 110 °C if NAVMAT guidelines are to be followed. Figures 16 and 17 show the tradeoff that must be made be- tween the highest allowable pulsed output power and the pulse length. Notice that for each curve, as the pulse length is made longer, the pulsed power that causes a 110 °C junction tem- perature to be reached is lower. The curves are provided for two baseplate temperatures (25 °C and 90°C) and three average output powers. The duty cycle that corresponds to any point on a curve can be calculated by dividing the average power by the pulsed power for that point. The curves represent typical upper limits; operation anywhere below the curves is accept- able and will result in cooler junctions. The ADDC02808PB is designed to deliver a continuous 100 watts to its output while keeping its hottest junction tempera- ture below 110 °C with a baseplate temperature of 90°C. PULSEWIDTH – ms 250 200 0 0 700 100 200 300 400 500 600 150 100 50 MAXIMUM PEAK POWER LIMIT MAXIMUM CONTINUOUS POWER LIMIT 100W ave 50W ave 10W ave Figure 16. Largest On-State Power vs. Pulsewidth that Maintains TJMAX ≤ 110 °C at 25 °C Baseplate |
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