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PI2001 Datasheet(PDF) 6 Page - Vicor Corporation |
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PI2001 Datasheet(HTML) 6 Page - Vicor Corporation |
6 / 23 page Functional Description: The PI2001 Cool-ORing controller IC is designed to drive single or paralleled N-channel MOSFETs in Active ORing applications. The PI2001 used with an external MOSFET can function as an ideal ORing diode in the high or low side of a redundant power system, significantly reducing power dissipation and eliminating the need for heatsinking. An N-channel MOSFET in the conduction path offers extremely low on-resistance resulting in a dramatic reduction of power dissipation versus the performance of a diode used in conventional ORing applications due to its high forward voltage drop. This can allow for the elimination of complex heat sinking and other thermal management requirements. Due to the inherent characteristics of the MOSFET, while the gate remains enhanced above the gate threshold voltage it will allow current to flow in the forward and reverse direction. Ideal ORing applications do not allow for reverse current flow, so the controller has to be capable of very fast and accurate detection of reverse current caused by input power source failures, and turn off the gate of the MOSFET as quickly as possible. Once the gate voltage falls below the gate threshold, the MOSFET is off and the body diode will be reverse biased preventing reverse current flow and subsequent excessive voltage droop on the redundant bus. During forward over-current conditions caused by load faults, the controller maintains gate drive to the MOSFET to keep power dissipation as low as possible, otherwise the inherent body diode of the MOSFET would conduct, which has higher effective forward drop. Conventional ORing solutions using diodes offer no protection against forward over- current conditions. During the forward over-current condition, the PI2001 will provide an active-low fault flag to the system via the FT pin. The fault flag is also issued during the reverse current condition, light load conditions, VC Under-Voltage, Input Under-Voltage and Over-Voltage and Over- Temperature conditions. Differential Amplifier: The PI2001 integrates a high-speed low offset voltage differential amplifier to sense the difference between the Sense Positive (SP) pin voltage and Sense Negative (SN) pin voltage with high accuracy. The amplifier output is connected to three comparators: Reverse comparator, Forward comparator, and Forward over-current comparator. Reverse Comparator: RVS The reverse comparator is the most critical comparator. It looks for negative voltage caused by reverse current. When the SN pin is 6mV higher than the SP pin, the reverse comparator will enable the BK current source to charge an internal 2pF capacitor. The blanking timer provides noise filtering for typical switching power conversion that might cause premature reverse current detection. Once the voltage across the capacitor reaches the timer threshold voltage (1.25V) the gate will be discharged by a 4Apk current. The shortest blanking time is 50ns when BK is connected to ground. The Blanking time programmed by the BK pin will be added to the controller delay time. The Electrical Specifications in the DIFFERENTIAL AMPLIFIER AND COMPARATOR section for Reverse Fault to Slave Low Delay Time “tRVS-MS or tRVS-SL” is the controller delay time plus the blanking time. Reverse Blanking Timer: BK Connecting an external resistor ( ) between the BK pin and ground will increase the blanking time as shown in Figure 2. BK R Where: Ω ≤ K R BK 200 If BK is connected to VC for slave mode operation, then the blanking time will be about 320ns typically, and total delay time will be 430ns. The reverse comparator has 3mV of hysteresis referenced to SP-SN. If the conditions are met for a reverse current fault, then the active-low fault flag output will also indicate a fault to the system after the 40µs fault delay time. Figure 2: Blanking time vs. BK resistor value Picor Corporation • picorpower.com PI2001 Rev 1.0 Page 6 of 23 |
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