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Moteur de recherche de fiches techniques de composants électroniques |
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FAN1655M Fiches technique(PDF) 5 Page - Fairchild Semiconductor |
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FAN1655M Fiches technique(HTML) 5 Page - Fairchild Semiconductor |
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5 / 9 page  FAN1655 PRODUCT SPECIFICATION REV. 1.1.4 3/24/04 5 Applications Information Output Capacitor selection The JEDEC specification for DDR termination requires that VTT stay within ±40mV of VREF, which must track VDDQ/2 within 1%. During the initial load transient, the output capacitor keeps the output within spec. To stay within the 40mV window, the “load step” due to the load transient current dropping across the output capacitor’s ESR should be kept to around 25mV: where ESR < is given in m Ω, and ∆I is the maximum load current. For example, to handle a 3A maximum load transient, the ESR should be no greater than 8m Ω. Furthermore, the output capacitor must be able to hold the load in spec while the regulator recovers (about 15µS). A minimum value of 470µF is recommended. These requirements can be achieved by a combination of capacitors. FAN1655 requires a minimum of 5m Ω of ESR in the output and is not stable with all-ceramic output capacitors. Power Dissipation and Derating The maximum output current (sink or source) for a 1.25V output is: where PD(MAX) is the maximum power dissipation which is: where TJ(MAX) is the maximum die temperature of the IC and TA is the operating ambient temperature. FAN1655 has an internal thermal limit at 150°C, which defines TJ(MAX). For the SOIC-14 package, θJA is given at 88°C/W. Using equation 2, the maximum dissipation at TA = 25°C is 1.4W, which is its rated maximum dissipation. The e-TSSOP or MLP package, however, use the PCB copper to cool the IC through the thermal pad on the package bottom. For maximum dissipation, this pad should be soldered to the PCB copper, with as much copper area as possible surrounding it to cool the package. Thermal vias should be placed as close to the thermal pad as possible to transfer heat to other layers of copper on the PCB. With large areas of PCB copper for heat sinking, a θJA of under 40°C/W can easily be achieved. 25 ∆I ------ I OUT MAX () P D MAX () 1.25 ---------------------- = (1) P D MAX () T J MAX () TA – θ JA ---------------------------------- = (2) |
Numéro de pièce similaire - FAN1655M |
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Description similaire - FAN1655M |
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