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ISL6323BCRZ Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL6323BCRZ Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 35 page  11 FN6879.0 March 23, 2009 ISEN_NB-, ISEN_NB+ These pins are used for differentially sensing the North Bridge output current. The sensed current is used for protection and load line regulation if droop is enabled. Connect ISEN_NB- to the node between the RC sense element surrounding the inductor. Tie the ISEN_NB+ pin to the VNB side of the sense capacitor. UGATE_NB Connect this pin to the corresponding upper MOSFET gate. This pin provides the PWM-controlled gate drive for the upper MOSFET and is monitored for shoot-through prevention purposes. BOOT_NB This pin provides the bias voltage for the corresponding upper MOSFET drive. Connect this pin to appropriately- chosen external bootstrap capacitor. The internal bootstrap diode connected to the PVCC_NB pin provides the necessary bootstrap charge. PHASE_NB Connect this pin to the source of the corresponding upper MOSFET. This pin is the return path for the upper MOSFET drive. This pin is used to monitor the voltage drop across the upper MOSFET for overcurrent protection. LGATE_NB Connect this pin to the corresponding MOSFET’s gate. This pin provides the PWM-controlled gate drive for the lower MOSFET. This pin is also monitored by the adaptive shoot-through protection circuitry to determine when the lower MOSFET has turned off. Operation The ISL6323B utilizes a multi-phase architecture to provide a low cost, space saving power conversion solution for the processor core voltage. The controller also implements a simple single phase architecture to provide the Northbridge voltage on the same chip. 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 that is both cost-effective and thermally viable have forced a change to the cost-saving approach of multi-phase. The ISL6323B controller helps simplify implementation by integrating vital functions and requiring minimal external components. The “Controller Block Diagram” on page 3 provides a top level view of the multi-phase power conversion using the ISL6323B 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 2 and 3). 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 Equation 2, which represents an individual channel peak-to-peak inductor current. In Equation 2, VIN and VOUT are the input and output voltages respectively, L is the single-channel inductor value, and fS is the switching frequency. The output capacitors conduct the ripple component of the inductor current. In the case of multi-phase converters, the capacitor current is the sum of the ripple currents from each of the individual channels. Compare Equation 2 to the expression for the peak-to-peak current after the summation of N symmetrically phase-shifted inductor currents in Equation 3. Peak-to-peak ripple current decreases by an amount proportional to the number of channels. Output-voltage ripple is a function of capacitance, capacitor FIGURE 1. PWM AND INDUCTOR-CURRENT WAVEFORMS FOR 3-PHASE CONVERTER 1 μs/DIV PWM2, 5V/DIV PWM1, 5V/DIV IL2, 7A/DIV IL1, 7A/DIV IL1 + IL2 + IL3, 7A/DIV IL3, 7A/DIV PWM3, 5V/DIV I P-P V IN V OUT – () V OUT Lf S VIN ------------------------------------------------------ = (EQ. 2) ISL6323B ISL6323B |
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