Ideal-diode-ORing & hot swap controller monitors current

January 08, 2016 // By Graham Prophet
LTC4236 is a dual ideal-diode-OR and single Hot Swap controller with a load current monitoring output, designed for use on the power circuit boards of high availability systems (servers, network routers, and solid-state drives), with multiple power supply feeds.

It combines (diode-ORs) feeds from two power supplies while providing inrush current control, overcurrent protection, and current monitoring, in a compact footprint. For supply ORing, low-loss N-channel MOSFETs replace power Schottky diodes and associated heat sinks, reducing voltage drop, power loss and solution area. The downstream hot swap MOSFET facilitates safe board insertion and removal from a live backplane, and protects from short-circuit faults with a fast acting current-limited circuit breaker. A low-offset ground-referenced output signal enables load current measurement with an external analogue-to-digital converter.

The LTC4236 regulates a low 15 mV forward voltage drop across the ideal diode MOSFETs to prevent DC reverse current while ensuring smooth current transfer during supply switchover. Ideal-diode fast turn-on and turn-off minimises output voltage droop and transient reverse current. A diode-off input and back-to-back MOSFET capability enable supply prioritisation, important when ORing a main supply with a higher voltage auxiliary supply or battery. In an output short-circuit, the LTC4236 further reduces its 25 mV current limit and runs an adjustable timer to limit MOSFET power dissipation. For application flexibility, the connector debounce filter delay is fixed internally or adjustable with an external capacitor.

The LTC4236 is available in two options: the LTC4236-1 remains off after an overcurrent fault, whereas the LTC4236-2 automatically turns on with a 0.15% duty cycle. Specified over the 0°C to 70°C commercial and -40°C to 85°C industrial temperature ranges, the LTC4236 comes in a 28-pin 4 x 5 mm QFN package for $4.25 (1000).

Linear Technology; www.linear.com/product/LTC4236

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