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BBF2805SH Datasheet(PDF) 7 Page - M.S. Kennedy Corporation |
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BBF2805SH Datasheet(HTML) 7 Page - M.S. Kennedy Corporation |
7 / 11 page APPLICATION NOTES POWER SUPPLIES The output voltage of the BBF2800S may be adjusted from 90% to 110% of nominal value by the use of a 50K Ω potenti- ometer as shown. Adjustment beyond this range is possible however certain characteristics of the converter such as but not limited to input voltage range, efficiency, ripple and tem- perature performance will change. Characterization by the user is recommended in such applications. Adjust/comp (pin 4) may be driven by external circuitry refer- enced to pin 8 (-output sense) if desired. Grounding pin 4 causes output voltage to increase (25% typically) while driving pin 4 above 1.3V causes output voltage to decrease. Pin 4 may be driven through 10K Ω or more if connection of the comp function is also required. The comp function of pin 4 allows transient response and phase margin to be tailored to suit a specific application. This feature may be utilized by connecting a small (1-500nF) capaci- tor between pins 4 and 6 or 7. This is generally recommended when very large low ESR load capacitances are used. Rev. F 12/06 7 SHUTDOWN PLUS Pin 2 is used for remote shutdown, output fault detection, and/or setting the input voltage point at which the converter will turn on as shown in the typical application diagram. No connection to pin 2 is necessary for normal operation of the converter. Pin 2 is referenced to pin 12 (-input). Shutdown may be implemented by simply connecting pin 2 to an open collector logic output or switch rated at 2.5mA, 25Vdc or higher. Input voltage turn on point is programmed with a single resis- tor from pin 2 to 12. An input turn on/off hysteresis (typically 3.5% of Vin) will be observed. This should be considered when making or verifying set point adjustment. The value of the setpoint resistor may be determined by the following: R= (±10% accuracy at 25°C) Set point temperature coefficient is typically +400ppm/°C. Output fault monitoring is accomplished by observing pin 2 with a high impedance monitoring circuit. Pin 2 voltage drops from over 10V to below 1V when a load fault causes the converters fault protection circuitry to activate. It will remain low for at least 100mS and return high. If the load fault is still present pin 2 will return low and the cycle will repeat. If there is no input setpoint programming resistor already in place a resistor >400K Ω from pin 2 to 12 will provide pin 2 pull down. 210·10³ ETO-9.5 MULTIPLE CONVERTER SYNCHRONIZATION Synchronized operation of up to three BBF2800S series con- verters may be accomplished without external components. One unit selected to be the master is connected normally with pin 10 grounded. The clock output pin 3 will provide the sync sig- nal for up to two slave units. The slave units have pin 10 not connected and receive the clock signal into pin 11. The clock signal lines may be shielded to prevent radiation. A separate 50 ohm coax to each slave unit is recommended in order to pre- serve signal integrity. Shield ends should be connected to pin 12 of the nearest converter. BBF2800S converters may also be synchronized to an exter- nal 500 KHz (+/- 5%) frequency source driving pin 11 of the converters. Pin 10 is not connected. The converters synchronize to the positive edge of the frequency source allowing a variety of wave forms (pulse, square, spike) to be used. Pin 11 is internally capacitively coupled allowing unipolar or bipolar fre- quency sources to be used. The source should have a waveform rise time of 20 ns or less and be capable of driving at least 4 volts peak into each 50 ohm pin 11 input (50 volts peak max). An externally synchronized unit may be used to synchronize other (slave) units. The slave units may be used in turn to synchronize other slave units from their pin 3 outputs. Each “generation” of slave units has a delay (100-200ns typical) from the unit that it is synchronizing to. |
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