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ISL6564CR Datasheet(PDF) 11 Page - Renesas Technology Corp |
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ISL6564CR Datasheet(HTML) 11 Page - Renesas Technology Corp |
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11 / 28 page  ISL6564 FN9156 Rev 2.00 Page 11 of 28 Dec 27, 2004 PGOOD PGOOD is used as an indication of the end of soft-start per the microprocessor specification. It is an open-drain logic output that is low impedance until the soft-start is completed. It will be pulled low again once the undervoltage point is reached. OFS The OFS pin provides a means to program a dc offset current for generating a dc offset voltage at the REF input. The offset current is generated via an external resistor and precision internal voltage references. The polarity of the offset is selected by connecting the resistor to GND or VCC. For no offset, the OFS pin should be left unterminated. OVP Overvoltage protection pin. This pin pulls to VCC and is latched when an overvoltage condition is detected. Connect this pin to the gate of an SCR or MOSFET tied from VIN or VOUT to ground to prevent damage to the load. This pin may be pulled above VCC as high as 15V to ground with an external resistor. However, it is only capable of pulling low when VCC is above 2V. DRVEN Driver enable pin. This pin can be used to enable the drivers which have enable pins such as ISL6605 or ISL6608. If ISL6564 is used with Intersil ISL6612 drivers, it’s not necessary to use this pin. IDROOP and IOUT IDROOP and IOUT are the output pins of sensed average channel current which is proportional to load current. They are designed for flexible application purposes. In the application which does not require loadline, leave IDROOP pin open. In the application which requires load line, connect IDROOP pin to FB so that the sensed average current will flow through the resistor between FB and VDIFF to create a voltage drop which is proportional to load current. IOUT is typically used for load current indication. Operation Multi-Phase Power Conversion Microprocessor load current profiles have changed to the point that the advantages of multi-phase power conversion are impossible to ignore. The technical challenges associated with producing a single-phase converter which is both cost-effective and thermally viable have forced a change to the cost-saving approach of multi-phase. The ISL6564 controller helps reduce the complexity of implementation by integrating vital functions and requiring minimal output components. The block diagrams on pages 3, 4, 5 and 6 provide top level views of multi-phase power conversion using the ISL6564 controller. Interleaving The switching of each channel in a multi-phase converter is timed to be symmetrically out of phase with each of the other channels. In a 3-phase converter, each channel switches 1/3 cycle after the previous channel and 1/3 cycle before the following channel. As a result, the three-phase converter has a combined ripple frequency three times greater than the ripple frequency of any one phase. In addition, the peak-to- peak amplitude of the combined inductor currents is reduced in proportion to the number of phases (Equations 1 and 2). Increased ripple frequency and lower ripple amplitude mean that the designer can use less per-channel inductance and lower total output capacitance for any performance specification. Figure 1 illustrates the multiplicative effect on output ripple frequency. The three channel currents (IL1, IL2, and IL3) combine to form the AC ripple current and the DC load current. The ripple component has three times the ripple frequency of each individual channel current. Each PWM pulse is terminated 1/3 of a cycle after the PWM pulse of the previous phase. The peak-to-peak current for each phase is about 7A, and the dc components of the inductor currents combine to feed the load. To understand the reduction of ripple current amplitude in the multi-phase circuit, examine the equation representing an individual channel’s peak-to-peak inductor current. In Equation 1, VIN and VOUT are the input and output voltages respectively, L is the single-channel inductor value, and fS is the switching frequency. FIGURE 1. PWM AND INDUCTOR-CURRENT WAVEFORMS FOR 3-PHASE CONVERTER 1µs/DIV PWM2, 5V/DIV PWM1, 5V/DIV IL2, 7A/DIV IL1, 7A/DIV IL1 + IL2 + IL3, 7A/DIV IL3, 7A/DIV PWM3, 5V/DIV IPP VIN VOUT – V OUT LfS VIN ------------------------------------------------------ = (EQ. 1) |
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