ORing IC Cuts Power Loss By 85%

April 14, 2005
A universal high-speed controller/N-channel power MOSFET driver for high-performance active ORing circuits has been developed by International Rectifier...

A universal high-speed controller/N-channel power MOSFET driver for high-performance active ORing circuits has been developed by International Rectifier.

The active ORing IC is used with an external MOSFET, replacing traditional diode ORing to increase efficiency and reduce power dissipation, says the company. Active ORing is needed for high-end systems requiring maximum up-time, such as carrier-class communication equipment and telecom and datacom system servers.

The IR5001S also provides diagnostic features that increase system up-time. Active ORing combines two or more power sources to create a redundant power source, preserving the input power supply in case one of the input sources fails. In the event of an input power failure, the active ORing circuit disconnects the non-functioning power source as quickly as possible to prevent the system bus voltage from falling, and to prevent large peak reverse currents.

The active ORing controller IC is suitable for a range of active ORing circuits, including -48V/-24V input active ORing for carrier-class communication equipment, 24V/48V output active ORing for redundant AC-DC rectifiers, 12V output active ORing for multiple-output DC-DC and AC-DC power and for low voltage output redundant VRM DC-DC processor power.

In 12V output systems, ORing circuits capable of handling currents of 100A can be made using four IRF6609 DirectFET MOSFETs in parallel. The IR5001S can also be used in reverse polarity applications for 48V/24V systems, replacing large D2Pak style diodes and an expensive relay.

When using the IR5001S with the 100V IRF6655 DirectFET MOSFET, 30W to 60W board power levels can be addressed. The IRF6655 in the small can package offers a space reduction of about 50% versus solutions in an SO-8 package, and is more appropriate for lower power applications. The 100V IRF6644 DirectFET MOSFET in the medium can package can also be used for higher power applications, up to about 250W to 300W board power levels, eliminating the need to use multiple SO-8 devices in parallel or larger single package devices.

With the addition of a charge pump circuit, the IR5001S can also be implemented in ground ORing in -48V systems, as required by the Advanced Telecom Computing Architecture (ATCA) specification.

The input terminals (INN and INP) are used to determine the output voltage by measuring the differential voltage and polarity across the drain and source terminals of the external MOSFET. The output voltage (Voutof the IC drives the gate of the external MOSFET. If the current reverses polarity, the IC will quickly switch the active ORing MOSFET off by pulling the Vout pin low.

The turn-off delay for IR5001S is typically 130nS, with a typical 20ns FET turn-off time that cuts voltage sags on the redundant bus voltage. Usually the reverse polarity protection circuitry is mounted on the rack or panel in the system and not on-board. Since this solution is so small, the circuit can be mounted on-board, which can significantly simplify system design.

The IR5001S IC includes diagnostic pins (FET Check “FETch” and FET Status “FETst”) to determine the status of the active ORing circuit. This is important for systems that require the highest level of up-time. When a logic signal is sent to the FET Check pin, the output of the IR5001S (Vout), or the gate drive to the MOSFET, will pull low, turning the MOSFET off.

This momentary off period should cause the voltage across the drain-to-source terminals of the MOSFET to increase, as the current is diverted from the MOSFET channel to the body drain diode. If the voltage rises from approximately

Asymmetrical offset voltage prevents output oscillations under light load, increasing reliability. The driver IC can be powered from either a 36V to 75V universal telecom bus voltage (100V max.) or from an external bias supply and a bias resistor for design flexibility. The IR5001S can also withstand continuous gate short conditions, and up to 100V continuous on the input pins, enabling reliable operation.

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