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ADDC02808PB Folha de dados(PDF) 11 Page - Analog Devices |
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ADDC02808PB Folha de dados(HTML) 11 Page - Analog Devices |
11 / 20 page ADDC02808PB REV. 0 –11– not have the response depicted in the last section. This is because the feedback integrator will not have had time to return to its normal state, and so the converter’s ability to respond to a positive step change in load current will be reduced. The maximum negative going deviation in the output voltage under this circumstance will then be greater than is shown in the figures of that section. Should this situation arise, one approach would be to step the load current down to an intermediate value (e.g., 4 A) at the end of the power pulse, and then let this current decay to a smaller value (e.g., 0.1 A) with a time constant in the 100 µs to 200 µs range. This should permit a rapid return to a steady state condition at the end of the power pulse without requiring a large average load current during the low power portion of the cycle. PIN CONNECTIONS Pins 1 and 2 ( SENSE) Pins 1 and 2 must always be connected for proper operation, although failure to make these connections will not be cata- strophic to the converter under normal operating conditions. Pin 1 must always be connected to the output return and Pin 2 must always be connected to +VOUT. These connections can be made at any one of the output pins of the converter, or remotely at the load. A remote connection at the load can adjust for voltage drops of as much as 0.25 V dc between the converter and the load. Long remote sense leads can affect converter stability, although this condition is rare. The impedance of the long power leads between the converter and the remote sense point could affect the converter’s unity gain crossover frequency and phase margin. Consult factory if long remote sense leads are to be used. Pin 3 (ADJUST) An adjustment pin is provided so that the user can change the nominal output voltage during the prototype stage. Since very low temperature coefficient resistors are used to set the output voltage and maintain tight regulation over temperature, using standard external resistors to adjust the output voltage will loosen output regulation over temperature. Furthermore, since the status trip point is not changed when the output voltage is adjusted using external resistors, the status line will no longer trip at the standard levels of the newly adjusted output voltage. If necessary, modified standard units can be ordered with the necessary changes made inside the package at the factory. The ADJUST function is sensitive to noise, and care should be taken in the routing of connections. To make the output voltage higher, place a resistor from ADJUST (Pin 3) to –SENSE (Pin 1). To make the output voltage lower, place a resistor from ADJUST (Pin 3) to +SENSE (Pin 2). Figures 30 and 31 show resistor values for a ±5% change in output voltage. With regard to the range that the output voltage can be adjusted by the user, there are two concerns. As the output voltage is raised it may become difficult to maintain regulation at full power and low input voltage. As the output voltage is lowered, it may become difficult to maintain regulation at minimum power and high input line. OUTPUT VOLTAGE – % 8 7 1 99 95 98 97 96 5 4 3 2 6 Figure 30. External Resistor Value for Reducing Output Voltage OUTPUT VOLTAGE – % 5 4 0 101 105 102 103 104 3 2 1 Figure 31. External Resistor for Increasing Output Voltage Pin 4 (STATUS) Pin 4 is active high referenced to –SENSE (Pin 1), indicating that the output voltage is typically within ±5%. The pin is both pulled up and down by internal circuitry. Figures 32 and 33 show the typical source and sink capabilities of the status output. Refer to the paragraphs describing Pin 3 (ADJUST) for effect on status trip point. IOH – mA 5 4 0 0.2 1.6 0.4 0.6 0.8 1.0 1.2 1.4 3 2 1 Figure 32. Source Capability of Status Output OBSOLETE |
Nº de peça semelhante - ADDC02808PB_15 |
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Descrição semelhante - ADDC02808PB_15 |
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