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ISL6144IR Datasheet(PDF) 13 Page - Intersil Corporation |
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ISL6144IR Datasheet(HTML) 13 Page - Intersil Corporation |
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13 / 29 page  13 FN9131.3 February 15, 2007 Using the ISL6144EVAL1 High Voltage ORing MOSFET Controller Evaluation Board In a multiple supply, fault tolerant, redundant power distribution system, paralleled power supplies contribute equally to the load current through various power sharing schemes. Regardless of the scheme, a common design practice is to include discrete ORing power diodes to protect against reverse current flow should one of the power supplies develop a catastrophic output short to ground. In addition, reverse current can occur if the current sharing scheme fails and an individual power supply voltage falls significantly below the others. Although the discrete ORing diode solution has been used for some time and is inexpensive to implement, it has some drawbacks. The primary downside is the increased power dissipation loss in the ORing diodes as power requirements for systems increase. In some systems this lack of efficiency results in a cost that surpasses the cost of the ISL6144 and power FET implementation. The power loss across a typical ORing diode with 20A is about 10W. Many diodes will be paralleled to help distribute the heat. In comparison, a FET with 5m Ω on-resistance dissipates 2W, which constitutes an 80% reduction. When multiplied by the number of paralleled supplies, the power savings are significant. Another disadvantage when using an ORing diode would be failure to detect a shorted or open ORing diode, jeopardizing power system reliability. An open diode reduces the system to a single point of failure while a diode short might pose a hazard to technical personnel servicing the system while unaware of this failure. The ISL6144 ORing MOSFET Controller and a suitably sized N-Channel power MOSFET(s) increase power distribution efficiency and availability when replacing a power ORing diode in high current applications. It can be used in +10V to +75V systems and has an internal charge pump to provide a floating gate drive for the N-Channel ORing MOSFET. The input/output differential trip point “VOUT - VIN” can be programmed by two external resistors (R1, R2 or R6, R7). This trip point can be adjusted to avoid false gate trip off due to power supply noise. The high speed comparator action protects the common bus from being affected due to individual power supply shorts by turning off the ORing MOSFET of the shorted feed in less than 300ns (when using an ORing MOSFET with equivalent gate to source capacitance equal to 39nF). The Hysteretic Regulating (HR) Amplifier provides a slow turn-off of the ORing MOSFET. This turn-off is achieved in less than 100 μs when one of the sourcing power supplies is shutdown slowly for system diagnostics, ensuring zero reverse current. This slow turn-off mechanism also reacts to output voltage droop, degradation, or power-down. A circuit fault condition is indicated on an open drain FAULT pin. The fault detection circuitry covers different types of failures; including dead short in the sourcing supply, a dead- short of any two ORing MOSFET terminals, or a blown fuse in the power distribution path. Typical Application Related Literature • TB389 (PCB Land Pattern Design and Surface Mount Guidelines for QFN (MLFP) Packages) • Manufacturer’s MOSFET data sheets DC/DC VIN HVREF FAULT GND VOUT COMP VSET VPU ISL6144 C1 R3 C2 R1 R2 GATE 1 Q1 VOUT VIN1 10V TO 75V CS C6* C5* LED1 RED DC/DC VIN HVREF FAULT GND VOUT COMP VSET VPU ISL6144 C3 C4 R6 R7 GATE 2 Q1 VIN2 10V TO 75V C8* C7* LED2 RED PS_1 PS_2 U2 U1 C3 = C4 = 10nF (10V) C5* TO C8* = 100nF *(100V) Optional Decoupling Caps R1 = R6 = 499Ω (5%) R3 = R4 = 1.21kΩ (5%) R2 = R7 = 47.5kΩ (5%) C1 = C2 = 150nF (10V) R4 - VPU is an external pull up voltage source. Also, VOUT can be used as the pull up source. In this case if it is higher than 16V, use a zener diode from the FAULT pin to GND with a clamping - LED1, LED2 are red LEDs to indicate a fault, different interfaces are possible to the FAULT pin. voltage less than the rating of the FAULT pin which is 16V. ISL6144 |
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