MOSFET ideal diode controller
26 August 2008
For low voltage applications, this ideal diode controller enables low loss ORing of power sources.
The LTC4352 from Linear Technology claims to regulate the forward voltage drop across an external N-channel MOSFET to ensure smooth current transfer between supplies in diode-OR applications.
In low voltage systems, a slow hand-off between controllers usually results in a voltage droop during supply switchover. However, the 500ns turn-on time ensures smooth switchover from one path to the other without oscillation. In the event of the input supply failing or shorting, a fast turn-off minimises reverse current. In addition to redundant power supply ORing, the LTC4352, claims the manufacturer, makes a suitable diode replacement in supply hold-up applications where momentary collapse of supply voltage is isolated from the load.
Fast turn-on is achieved via charge stored on an external capacitor for immediate sourcing of gate pull-up current. The new model provides under/overvoltage monitoring and a FAULT# pin to indicate when the input supply is outside of proper levels or an open MOSFET fault has occurred, while a Status pin indicates the MOSFET on state. The ideal diode behaviour may be overridden to allow reverse current if desired. Furthermore, the LTC4352 can be used for inrush current control in applications where the input supply is hot-plugged.
In contrast to a standard diode, this ideal diode controller prevents out of range input voltages from affecting the load voltage by using back-to-back MOSFETs and resistive dividers on the UV and OV pins to set the allowable input voltage operating range. The controller operates with supplies from 2.9V to 18V, and offers additional flexibility to control voltages down to 0V by applying an external supply. It is available in 12pin MSOP and 3mm x 3mm DFN packages.
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