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ISL6327 数据表(PDF) 20 Page - Intersil Corporation |
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ISL6327 数据表(HTML) 20 Page - Intersil Corporation |
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20 / 30 page  20 FN9276.2 December 20, 2006 Undervoltage Detection The undervoltage threshold is set at 50% of the VID voltage. When the output voltage at VSEN is below the undervoltage threshold, VR_RDY gets pulled low. When the output voltage comes back to 60% of the VID voltage, VR_RDY will return back to high. Overvoltage Protection Regardless of the VR being enabled or not, the ISL6327 overvoltage protection (OVP) circuit will be active after its POR. The OVP thresholds are different under different operation conditions. When VR is not enabled and before the 2nd soft-start, the OVP threshold is 1.275V. Once the controller detects a valid VID input, the OVP trip point will be changed to the VID voltage plus 175mV. Two actions are taken by the ISL6327 to protect the microprocessor load when an overvoltage condition occurs. At the inception of an overvoltage event, all PWM outputs are commanded low instantly (less than 20ns). This causes the Intersil drivers to turn on the lower MOSFETs and pull the output voltage below a level to avoid damaging the load. When the VDIFF voltage falls below the DAC plus 75mV, PWM signals enter a high-impedance state. The Intersil drivers respond to the high-impedance input by turning off both upper and lower MOSFETs. If the overvoltage condition reoccurs, the ISL6327 will again command the lower MOSFETs to turn on. The ISL6327 will continue to protect the load in this fashion as long as the overvoltage condition occurs. Once an overvoltage condition is detected, normal PWM operation ceases until the ISL6327 is reset. Cycling the voltage on EN_PWR, EN_VTT or VCC below the POR- falling threshold will reset the controller. Cycling the VID codes will not reset the controller. Overcurrent Protection ISL6327 has two levels of overcurrent protection. Each phase is protected from a sustained overcurrent condition by limiting its peak current, while the combined phase currents are protected on an instantaneous basis. In instantaneous protection mode, the ISL6327 utilizes the sensed average current IAVG to detect an overcurrent condition. See the Channel-Current Balance section for more detail on how the average current is measured. The average current is continually compared with a constant 85µA reference current as shown in Figure 9. Once the average current exceeds the reference current, a comparator triggers the converter to shutdown. At the beginning of overcurrent shutdown, the controller places all PWM signals in a high-impedance state within 20ns commanding the Intersil MOSFET driver ICs to turn off both upper and lower MOSFETs. The system remains in this state a period of 4096 switching cycles. If the controller is still enabled at the end of this wait period, it will attempt a soft- start. If the fault remains, the trip-retry cycles will continue indefinitely (as shown in Figure 10) until either controller is disabled or the fault is cleared. Note that the energy delivered during trip-retry cycling is much less than during full-load operation, so there is no thermal hazard during this kind of operation. For the individual channel overcurrent protection, the ISL6327 continuously compares the sensed current signal of each channel with the 120µA reference current. If one channel current exceeds the reference current, ISL6327 will pull PWM signal of this channel to low for the rest of the switching cycle. This PWM signal can be turned on next cycle if the sensed channel current is less than the 120µA reference current. The peak current limit of individual channel will not trigger the converter to shutdown. The overcurrent protection level for the above two OCP modes can be adjusted by changing the value of current sensing resistors. In addition, ISL6327 can also adjust the average OCP threshold level by adjusting the value of the resistor from IOUT to GND. This provides additional safety for the voltage regulator. The following equation can be used to calculate the value of the resistor RIOUT based on the desired OCP level IAVG, OCP2. Current Sense Output The ISL6327 has 2 current sense output pins IDROOP and IOUT; They are identical. In typical application, IDROOP pin is connected to FB pin for the application where load line is required. IOUT pin was designed for load current measurement. As shown in typical application schematics on pages 4 and 5, load current information can be obtained by measuring the voltage at IOUT pin with a resistor connecting IOUT pin to the ground. When the programmable temperature compensation function of ISL6327 is properly 0A 0V 2ms/DIV OUTPUT CURRENT FIGURE 10. OVERCURRENT BEHAVIOR IN HICCUP MODE. FSW = 500kHz OUTPUT VOLTAGE R IOUT 2 I AVG OCP2 , ------------------------------- = (EQ. 17) ISL6327 |
类似零件编号 - ISL6327 |
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类似说明 - ISL6327 |
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