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MQFL-28VE-06S-Y-ES Datasheet(PDF) 10 Page - SynQor Worldwide Headquarters |
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MQFL-28VE-06S-Y-ES Datasheet(HTML) 10 Page - SynQor Worldwide Headquarters |
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10 / 19 page  Product # MQFL-28VE-06S Phone 1-888-567-9596 www.synqor.com Doc.# 005-0005209 Rev. 1 04/22/09 Page 10 Output: Current: 6V 17A MQFL-28VE-06S Technical Specification BASIC OPERATION AND FEATURES The MQFL DC/DC converter uses a two-stage power conversion topology. The first, or regulation, stage is a buck-converter that keeps the output voltage constant over variations in line, load, and temperature. The second, or isolation, stage uses transform- ers to provide the functions of input/output isolation and voltage transformation to achieve the output voltage required. In the MQFL-28VE series of converters the regulation stage is preceeded by a boost-converter that permits these converters to operate through various Military and Aircraft under-voltage transients. Further discussion of this feature can be found later in these notes. Both the regulation and the isolation stages switch at a fixed frequency for predictable EMI performance. The isolation stage switches at one half the frequency of the regulation stage, but due to the push-pull nature of this stage it creates a ripple at double its switching frequency. As a result, both the input and the output of the converter have a fundamental ripple frequency of about 550 kHz in the free-running mode. Rectification of the isolation stage’s output is accomplished with synchronous rectifiers. These devices, which are MOSFETs with a very low resistance, dissipate far less energy than would Schottky diodes. This is the primary reason why the MQFL converters have such high efficiency, particularly at low output voltages. Besides improving efficiency, the synchronous rectifiers permit operation down to zero load current. There is no longer a need for a minimum load, as is typical for converters that use diodes for rectification. The synchronous rectifiers actually permit a negative load current to flow back into the converter’s output terminals if the load is a source of short or long term energy. The MQFL convert- ers employ a “back-drive current limit” to keep this negative output terminal current small. There is a control circuit on both the input and output sides of the MQFL converter that determines the conduction state of the power switches. These circuits communicate with each other across the isolation barrier through a magnetically coupled device. No opto- isolators are used. A separate bias supply provides power to both the input and out- put control circuits. Among other things, this bias supply permits the converter to operate indefinitely into a short circuit and to avoid a hiccup mode, even under a tough start-up condition. An input under-voltage lockout feature with hysteresis is provided, as well as an input over-voltage shutdown. There is also an output current limit that is nearly constant as the load impedance decreases to a short circuit (i.e., there is not fold- back or fold-forward characteristic to the output current under this condition). When a load fault is removed, the output voltage rises exponentially to its nominal value without an overshoot. The MQFL converter’s control circuit does not implement an output over-voltage limit or an over-temperature shutdown. The following sections describe the use and operation of addi- tional control features provided by the MQFL converter. UNDER-VOLTAGE TRANSIENTS The MQFL-28VE series of DC/DC converters incorporate a special “boost-converter” stage that permits the converters to deliver full power through transients where its input voltage falls to as low as 5.5V. Normally, the boost-converter is non-operational, and the converter’s input voltage is passed directly to its pre-regulation stage (see the Block Diagram). When an under-voltage transient occurs, the boost-converter becomes operational, and it steps-up the input voltage to a value greater than 16V so that the nominal output voltage can be sustained. It is important to note that the boost-converter stage must first become “armed” before it can become operational. This “arming” occurs when the converter’s input voltage exceeds approximately 18V. The boost-converter then becomes operational whenever the input voltage drops below the arming voltage, and it will remain operational as long as the input voltage remains within the region shown in the Under-Voltage Transient Profile Page. If the input voltage drops below this transient profile, the boost- converter stage is not guaranteed to continue operating (it may, but it will protect itself from excessive stresses). Once the boost- converter stops operating, the converter’s input voltage will be reconnected directly to the input of the pre-regulator stage. The output voltage will therefore collapse unless the input voltage is 16V, or greater. Note: the boost-converter will not become re-armed for the next transient unless the input voltage once again exceeds approximately 18V. The transient profile shown on the Under-Voltage Transient Profile page is designed to comply (with appropriate margins) with all initial-engagement surges, starting or cranking voltage transients, and under-voltage surges specified in: • MIL-STD-704-8 (A through F) • RTCA/DO-160E • MIL-STD-1275B • DEF-STAN 61-5 (Part 6)/5 (operational portions) Any input voltage transient that fits within the Under-Voltage Transient Profile can be repeated after a delay that is at least four times longer than the duration of the previous transient. During the time when the boost-converter stage is operational, the converter’s efficiency is reduced and the input ripple current is increased. The lower the input voltage, the more these parameters are affected. |
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