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AFL2815D Datasheet(PDF) 8 Page - International Rectifier |
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AFL2815D Datasheet(HTML) 8 Page - International Rectifier |
8 / 12 page 8 www.irf.com AFL28XXD Series General Application Information The AFL28XXD series of converters are capable of providing large transient currents to user loads on demand. Because the nominal input voltage range in this series is relatively low, the resulting input current demands will be correspondingly large. It is important therefore, that the line impedance be kept very low to prevent steady state and transient input currents from degrading the supply voltage between the voltage source and the converter input. In applications requiring high static currents and large transients, it is recommended that the input leads be made of adequate size to minimize resistive losses, and that a good quality capacitor of approximately 100 µfd be connected directly across the input terminals to assure an adequately low impedance at the input terminals. Table I relates nominal resistance values and selected wire sizes. Figure V. Connection for V OUT Adjustment Input Filter Undervoltage Lockout The AFL28XXD series converters incorporate a two stage LC input filter whose elements dominate the input load impedance characteristic during the turn-on sequence. The input circuit is as shown in Figure IV. Figure IV. Input Filter Circuit A minimum voltage is required at the input of the converter to initiate operation. This voltage is set to 14V ± 0.5V. To preclude the possibility of noise or other variations at the input falsely initiating and halting converter operation, a hysteresis of approximately 1.0V is incorporated in this circuit. Thus if the input voltage droops to 13V ± 0.5V, the converter will shut down and remain inoperative until the input voltage returns to ≈14V. Output Voltage Adjust Connect R adj to + to increase, - to decrease Pin 1 Pin 2 900nH 130nH 6 µfd 11.2 µfd By use of the trim pin (10), the magnitude of output voltages can be adjusted over a limited range in either a positive or negative direction. Connecting a resistor between the trim pin and either the output return or the positive output will raise or lower the magnitude of output voltages. The span of output voltage adjustment is restricted to the limits shown in Table I. Enable 2 Share Trim - Vout Return + Vout To Loads R ADJ AFL28xxD 7 12 + - Table 1. Output Voltage Trim Values and Limits AFL2805D AFL2812D AFL2815D V out R adj V out R adj V out R adj 5.5 0 12.5 0 15.5 0 5.4 12.5K 12.4 47.5K 15.4 62.5K 5.3 33.3K 12.3 127K 15.3 167K 5.2 75K 12.2 285K 15.2 375K 5.1 200K 12.1 760K 15.1 1.0M 5.0 ∞ 12.0 ∞ 15.0 ∞ 4.9 190K 11.7 975K 14.6 1.2M 4.8 65K 11.3 288K 14.0 325K 4.7 23K 10.8 72.9K 13.5 117K 4.6 2.5K 10.6 29.9K 13.0 12.5K 4.583 0 10.417 0 12.917 0 Note that the nominal magnitude of output voltage resides in the middle of the table and the corresponding resistor value is set to ∞. To set the magnitude greater than nominal, the adjust resistor is connected to output return. To set the magnitude less than nominal, the adjust resistor is connected to the positive output. (Refer to Figure V.) For output voltage settings that are within the limits, but between those listed in Table I, it is suggested that the resistor values be determined empirically by selection or by use of a variable resistor. The value thus determined can then be replaced with a good quality fixed resistor for permanent installation. When use of this adjust feature is elected, the user should be aware that the temperature performance of the converter output voltage will be affected by the temperature performance of the resistor selected as the adjustment element and therefore, is advised to employ resistors with a tight temperature coefficient of resistance. |
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