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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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ISL6568CR Fiches technique(PDF) 14 Page - Intersil Corporation |
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ISL6568CR Fiches technique(HTML) 14 Page - Intersil Corporation |
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14 / 28 page  14 FN9187.3 July 25, 2005 Load-Line (Droop) Regulation Some microprocessor manufacturers require a precisely- controlled output impedance. This dependence of output voltage on load current is often termed “droop” or “load line” regulation. As shown in Figure 6, a voltage, VDROOP, proportional to the total current in all active channels, IOUT, feeds into the differential remote-sense amplifier. The resulting voltage at the output of the remote-sense amplifier is the sum of the output voltage and the droop voltage. As Equation 4 shows, feeding this voltage into the compensation network causes the regulator to adjust the output voltage so that it’s equal to the reference voltage minus the droop voltage. The droop voltage, VDROOP, is created by sensing the current through the output inductors. This is accomplished by using a continuous DCR current sensing method. Inductor windings have a characteristic distributed resistance or DCR (Direct Current Resistance). For simplicity, the inductor DCR is considered as a separate lumped quantity, as shown in Figure 7. The channel current, IL, flowing through the inductor, passes through the DCR. Equation 5 shows the s-domain equivalent voltage, VL, across the inductor. The inductor DCR is important because the voltage dropped across it is proportional to the channel current. By using a simple R-C network and a current sense amplifier, as shown in Figure 7, the voltage drop across all of the inductors’ DCRs can be extracted. The output of the current sense amplifier, VDROOP, can be shown to be proportional to the channel currents IL1 and IL2, shown in Equation 6. If the R-C network components are selected such that the R-C time constant matches the inductor L/DCR time constant, then VDROOP is equal to the sum of the voltage drops across the individual DCRs, multiplied by a gain. As Equation 7 shows, VDROOP is therefore proportional to the total output current, IOUT. By simply adjusting the value of RS, the load line can be set to any level, giving the converter the right amount of droop at all load currents. It may also be necessary to compensate for any changes in DCR due to temperature. These changes cause the load line to be skewed, and cause the R-C time constant to not match the L/DCR time constant. If this becomes a problem a simple negative temperature coefficient resistor network can be used in the place of RCOMP to compensate for the rise in DCR due to temperature. Note: An optional 10nF ceramic capacitor from the ISUM pin to the IREF pin is recommended to help reduce any noise affects on the current sense amplifier due to layout. Output-Voltage Offset Programming The ISL6568 allows the designer to accurately adjust the offset voltage by connecting a resistor, ROFS, from the OFS pin to VCC or GND. When ROFS is connected between OFS and VCC, the voltage across it is regulated to 1.5V. This causes a proportional current (IOFS) to flow into the OFS pin and out of the FB pin. If ROFS is connected to ground, the voltage across it is regulated to 0.5V, and IOFS flows into the FB pin and out of the OFS pin. The offset current flowing through the resistor between VDIFF and FB will generate the desired offset voltage which is equal to the product (IOFS x RFB). These functions are shown in Figures 8 and 9. VL s () IL sL DCR + ⋅ () ⋅ = (EQ. 5) VDROOP s () sL ⋅ DCR ------------- 1 + sRCOMP CCOMP ⋅⋅ 1 + () -------------------------------------------------------------------------- RCOMP RS ----------------------- IL1 IL2 + () DCR ⋅⋅ ⋅ = (EQ. 6) VDROOP RCOMP RS --------------------- IOUT DCR ⋅⋅ = (EQ. 7) FIGURE 7. DCR SENSING CONFIGURATION ICOMP DCR L INDUCTOR VOUT COUT IL1 VL(s) DCR L INDUCTOR PHASE1 PHASE2 IL2 RS RS RCOMP CCOMP ISUM IREF ISL6568 - + VDROOP IOUT (optional) ISL6568 |
Numéro de pièce similaire - ISL6568CR |
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Description similaire - ISL6568CR |
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