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ISL8121IRZ Datasheet(PDF) 9 Page - Intersil Corporation |
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ISL8121IRZ Datasheet(HTML) 9 Page - Intersil Corporation |
9 / 26 page 9 FN6352.1 October 18, 2006 Operation Figure 2 shows a simplified diagram of the voltage regulation and current loops. The voltage loop is used to precisely regulate the output voltage, while the current feedback is used to balance the output currents, IL1 and IL2, of the two power channels. VOLTAGE LOOP Feedback from the output voltage is fed via the on-board differential amplifier and applied via resistor R1 to the inverting input of the Error Amplifier. The signal generated by the error amplifier is summed up with the current correction error signal and applied to the positive inputs of the PWM circuit comparators. Out-of-phase sawtooth signals are applied to the two PWM comparators inverting inputs. Increasing error amplifier voltage results in increased duty cycle. This increased duty cycle signal is passed to the output drivers with no phase reversal to drive the external MOSFETs. Increased duty cycle, translating to increased ON-time for the upper MOSFET transistor, results in increased output voltage, compensating for the low output voltage which lead to the increase in the error signal in the first place. CURRENT LOOP The current control loop is only used to finely adjust the individual channel duty cycle, in order to balance the current carried by each phase. The information used for this control is the voltage that is developed across rDS(ON) of each lower MOSFET, while they are conducting. A resistor converts and scales the voltage across each MOSFET to a current that is applied to the current sensing circuits within the ISL8121. Output from these sensing circuits is averaged and used to compute a current error signal. Each PWM channel receives a current signal proportional to the difference between the average sensed current and the individual channel current. When a PWM channel’s current is greater than the average current, the signal applied via the summing correction circuit to the PWM comparator reduces the output pulse width (duty cycle) of the comparator to compensate for the detected above average current in the respective channel. MULTI-PHASE POWER CONVERSION Multi-phase power conversion provides a cost-effective power solution when load currents are no longer easily supported by single-phase converters. Although its greater complexity presents additional technical challenges, the multi-phase approach offers advantages with improved response time, superior ripple cancellation, and thermal distribution. FIGURE 2. SIMPLIFIED BLOCK DIAGRAM OF THE ISL8121 VOLTAGE AND CURRENT CONTROL LOOPS AVERAGE Σ Σ Σ REFERENCE PWM CIRCUIT PWM CIRCUIT HALF-BRIDGE DRIVE HALF-BRIDGE DRIVE Σ OSCILLATOR COMP FB L1 L2 COUT VOUT VIN VIN RISEN2 UG1 UG2 LG1 LG2 ISEN1 ISEN2 CURRENT SENSE R1 R2 C1 PHASE1 CURRENT SENSE PHASE2 RISEN1 ISL8121 VDIFF VSEN+ VSEN- ISL8121 ISL8121 |
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