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ADDC02828SATV 데이터시트(PDF) 9 Page - Analog Devices |
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ADDC02828SATV 데이터시트(HTML) 9 Page - Analog Devices |
9 / 16 page ADDC02828SA REV. 0 –9– VIL – V 1.2 1.1 0.7 0.5 2.0 1.0 1.5 1.0 0.9 0.8 Figure 21. Input Characteristics of Pin 6 When Pulled Low Pin 7 (SYNC) Pin 7 can be used for connecting multiple converters to a mas- ter clock. This master clock can be either an externally user- supplied clock or it can be a converter that has been modified and designated as a master unit. Consult factory for availability of these devices. Capacitive coupling of the clock signal will ensure that if the master clock stops working the individual units will continue to operate at their own internal clock fre- quency, thereby eliminating a potential single point failure. Capacitive coupling will also permit a wider duty cycle to be used. The SYNC pin has an internal pull-down so it is not necessary to sink any current when driving the pin low. Reference Figure 28 for a fault tolerant, secondary side powered SYNC drive circuit. For user-supplied master clocks with no external circuitry, the following specifications must be met: a. Frequency: 1.00 MHz min b. Duty cycle: 7% min, 14% max c. High state voltage high level: 4 V min to 7 V max d. Low state voltage low level: 0 V min to 3.0 V max Users should note that the SYNC pin is referenced to the input return of the converter. If the user-supplied master clock is generated on the output side of the converter, the signal should be isolated. Users should be careful about the frequency selected for the external master clock. Higher switching frequencies will reduce efficiency and may reduce the amount of output power available at minimum input line. Consult factory for modified standard switch- ing frequency to accommodate system clock characteristics. Pin 8 (ISHARE) Pin 8 allows paralleled converters to share the total load cur- rent, typically within ±5% at full load. To use the current share feature, connect all current share pins to each other and con- nect the SENSE pins on each of the converters. The current sharing function is sensitive to the differential voltage between the input return pins of paralleled converters. The current sharing function is also sensitive to noise, and care should be taken in the routing of connections. Refer to Figure 27 for typical appli- cation circuits using paralleled converters. Pin 9 (TEMP) Pin 9 can be used to indicate case temperature or to raise or disable the temperature at which thermal shutdown occurs. Typically, 3.90 V corresponds to +25 °C, with a +13.1 mV/°C change for every 1 °C rise. The sensor IC (connected from Pin 9 to the input return [Pin 10]) has a 13.1 k Ω impedance. The thermal shutdown feature has been set to shut down the converter when the case temperature is nominally 110 °C to 115 °C. To raise the temperature at which shutdown occurs, connect a resistor with the value shown in Figure 22 from Pin 9 to the input return (Pin 10). To completely disable the tem- perature shutdown feature, connect a 50 k Ω resistor from Pin 9 to the input return (Pin 10). SHUTDOWN CASE TEMPERATURE – °C 1400 0 120 150 125 130 135 140 145 1200 1000 800 400 200 600 Figure 22. External Resistor Value for Raising Temperature Shutdown Point INPUT VOLTAGE RANGE The steady state operating input voltage range for the converter is defined as 18 V to 40 V. The abnormal operating input volt- age range is defined as 16 V to 50 V. In accordance with MIL- STD-704D, the converter can operate up to 50 V dc input for transient conditions as long as 50 milliseconds, and it can oper- ate down to 16 V dc input for continuous operation during emergency conditions. Figure 3 (typical low line dropout vs. load) shows that the converter can work continuously down to and below 16 V dc under reduced load conditions. The ADDC02828SA can be modified to survive, but not work through, the upper limit input voltages defined in MIL-STD-704A (aircraft) and MIL-STD-1275A (military vehicles). MIL-STD-704A defines an 80 V surge that lasts for 1 second before it falls below 50 V, while MIL-STD-1275A defines a 100 V surge that lasts for 200 milliseconds before it falls below 50 V. In both cases, the ADDC02828SA can be modified to operate to specification up to the 50 V input voltage limit and to shut down and protect itself during the time the input voltage exceeds 50 V. When the input voltage falls below 50 V as the surge ends, the converter will automatically initiate a soft start. In order to survive these higher input voltage surges; the modified converter, however, will no longer have input transient protection as described below. Contact the factory for information on units surviving high input voltage surges. Input Voltage Transient Protection: The converter has a transient voltage suppressor connected across its input leads to protect the unit against high voltage pulses (both positive and negative) of short duration. With the power supply connected in the typical system setup shown in Figure 15, a transient voltage pulse is created across the converter in the following manner. A 20 µF capacitor is first charged to 400 V. It is then connected directly across the converter’s end of the two meter power lead cable through a 2 Ω on-state resistance MOSFET. |
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