Electronic Components Datasheet Search |
|
AHP2812S Datasheet(PDF) 9 Page - International Rectifier |
|
AHP2812S Datasheet(HTML) 9 Page - International Rectifier |
9 / 12 page www.irf.com 9 AHP28XXS Series Attempts to adjust the output voltage to a value greater than 120% of nominal should be avoided because of the potential of exceeding internal component stress ratings and subsequent operation to failure. Under no circumstance should the external setting resistor be made less than 500 Ω. By remaining within this specified range of values, completely safe operation fully within normal component derating is assured. Examination of the equation relating output voltage and resistor value reveals a special benefit of the circuit topology utilized for remote sensing of output voltage in the AHP28XXS series of converters. It is apparent that as the resistance increases, the output voltage approaches the nominal set value of the device. In fact the calculated limiting value of output voltage as the adjusting resistor becomes very large is ≅ 250mV above nominal device voltage. The consequence is that if the +sense connection is unintentionally broken, an AHP28XXS has a fail-safe output voltage of Vout + 250mV, where the 250mV is independent of the nominal output voltage. It can be further demonstrated that in the event of both the + and - sense connections being broken, the output will be limited to Vout + 500mV. This 500mV is also essentially constant independent of the nominal output voltage. While operation in this condition is not damaging to the device, not all performance parameters will be met. General Application Information The AHP28XXS 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 approximately100 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. Table 1. Nominal Resistance of Cu Wire Wire Size, AWG Resistance per ft 24 Ga 25.7 m Ω 22 Ga 16.2 m Ω 20 Ga 10.1 m Ω 18 Ga 6.4 m Ω 16 Ga 4.0 m Ω 14 Ga 2.5 m Ω 12 Ga 1.6 m Ω As an example of the effects of parasitic resistance, consider an AHP2815S operating at full power of 120 W. From the specification sheet, this device has a minimum efficiency of 83% which represents an input power of more than 145 W. If we consider the case where line voltage is at its minimum of 16 volts, the steady state input current necessary for this example will be slightly greater than 9 amperes. If this device were connected to a voltage source with 10 feet of 20 gauge wire, the round trip (input and return) would result in 0.2 Ω of resistance and 1.8 volts of drop from the source to the converter. To assure 16 volts at the input, a source closer to 18 volts would be required. In applications using the paralleling option, this drop will be multiplied by the number of paralleled devices. By choosing 14 or 16 gauge wire in this example, the parasitic resistance and resulting voltage drop will be reduced to 25% or 31% of that with 20 gauge wire. Another potential problem resulting from parasitically induced voltage drop on the input lines is with regard to the operation of the enable 1 port. The minimum and maximum operating levels required to operate this port are specified with respect to the input common return line at the converter. If a logic signal is generated with respect to a ‘common’ that is distant from the converter, the effects of the voltage drop over the return line must be considered when establishing the worst case TTL switching levels. These drops will effectively impart a shift to the logic levels. In Figure VII, it can be seen that referred to system ground, the voltage on the input return pin is given by e Rtn = IRtn • RP |
Similar Part No. - AHP2812S |
|
Similar Description - AHP2812S |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.NET |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |