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ISL6314CRZ Datasheet(PDF) 11 Page - Intersil Corporation |
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ISL6314CRZ Datasheet(HTML) 11 Page - Intersil Corporation |
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11 / 32 page  11 FN6455.2 October 8, 2009 As Figure 2 shows, the APA circuitry works by monitoring the voltage on the APA pin and comparing it to a filtered copy of the voltage on the COMP pin. The voltage on the APA pin is a copy of the COMP pin voltage that has been negatively offset. If the APA pin exceeds the filtered COMP pin voltage an APA event occurs and the channel is forced on. The APA trip level is the amount of DC offset between the COMP pin and the APA pin. This is the voltage excursion that the APA and COMP pin must have during a transient event to activate the Adaptive Phase Alignment circuitry. This APA trip level is set through a resistor, RAPA, that connects from the APA pin to the COMP pin. A 100µA current flows across RAPA into the APA pin to set the APA trip level as described in Equation 3. An APA trip level of 500mV is recommended for most applications. A 1000pF capacitor, CAPA, should also be placed across the RAPA resistor to help with noise immunity. Active Pulse Positioning (APP) Modulated PWM Operation The ISL6314 uses a proprietary Active Pulse Positioning (APP) modulation scheme to control the internal PWM signals that command each channel’s driver to turn their upper and lower MOSFETs on and off. The time interval in which a PWM signal can occur is generated by an internal clock, whose cycle time is the inverse of the switching frequency set by the resistor connected to the FS pin. The advantage of Intersil’s proprietary Active Pulse Positioning (APP) modulator is that the PWM signal has the ability to turn on at any point during this PWM time interval, and turn off immediately after the PWM signal has transitioned high. This is important because is allows the controller to quickly respond to output voltage drops associated with current load spikes, while avoiding the ring back affects associated with other modulation schemes. The PWM output state is driven by the position of the error amplifier output signal, VCOMP, as illustrated in Figure 3. At the beginning of each PWM time interval, this VCOMP signal is compared to the internal modulator waveform. As long as the VCOMP voltage is lower then the modulator waveform voltage, the PWM signal is commanded low. The internal MOSFET driver detects the low state of the PWM signal and turns off the upper MOSFET and turns on the lower synchronous MOSFET. When the VCOMP voltage crosses the modulator ramp, the PWM output transitions high, turning off the synchronous MOSFET and turning on the upper MOSFET. The PWM signal will remain high until the VCOMP voltage crosses the modulator ramp again. When this occurs, the PWM signal will transition low again. During each PWM time interval, the PWM signal can only transition high once. Once PWM transitions high, it can not transition high again until the beginning of the next PWM time interval. This prevents the occurrence of double PWM pulses occurring during a single period. Output Voltage Setting The ISL6314 uses a digital to analog converter (DAC) to generate a reference voltage based on the logic signals at the VID pins. The DAC decodes the logic signals into one of the discrete voltages shown in Tables 2, 3 or 4. In the Intel VR11 mode of operation, each VID pin is pulled up to an internal 1.2V voltage by a weak current source (40µA), which decreases to 0A as the voltage at the VID pin varies from 0 to the internal 1.2V pull-up voltage. In AMD modes of operation, the VID pins are pulled low by a weak 20µA current source. External pull-up resistors or active-high output stages can augment the pull-up current sources, up to a voltage of 5V. . The ISL6314 accommodates three different DAC ranges: Intel VR11, AMD K8/K9 5-bit, and AMD 6-bit. The state of the SS and VID7 pins decide which DAC version is active. Refer to Table 1 for a description of how to select the desired DAC version. FIGURE 2. ADAPTIVE PHASE ALIGNMENT DETECTION EXTERNAL CIRCUIT ISL6314 INTERNAL CIRCUIT COMP VAPA,TRIP ERROR APA AMPLIFIER CAPA RAPA LOW FILTER - + APA PASS 100µA TO APA CIRCUITRY V APA TRIP , R APA 100 10 6 – × ⋅ = (EQ. 3) FIGURE 3. CHANNEL PWM FUNCTION - + PWM VCOMP TO GATE CONTROL LOGIC MODULATOR RAMP WAVEFORM ISL6314 ISL6314 |
Similar Part No. - ISL6314CRZ |
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