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LTC3720 - Single Phase VRM8.5 Current Mode Step-Down Controller

The LTC3720 is a synchronous step-down switching regulator controller for CPU power. An output voltage between 1.05V and 1.825V is selected by a 5-bit code (Intel VRM8.5 VID specification). The controller uses a valley current control architecture to deliver very low duty cycles without requiring a sense resistor. Operating frequency is selected by an external resistor and is compensated for variations in VIN and VOUT.

Discontinuous mode operation provides high efficiency operation at light loads. A forced continuous control pin reduces noise and RF interference and can assist secondary winding regulation by disabling discontinuous mode operation when the main output is lightly loaded.

Fault protection is provided by internal foldback current limiting, an output overvoltage comparator and optional short-circuit shutdown timer. Soft-start capability for supply sequencing is accomplished using an external timing capacitor. The regulator current limit level is also user programmable. Wide supply range allows operation from 4V to 36V at the input.

Features 5-Bit Programmable Output Voltage: 1.05V to 1.825V (VRM8.5) No Sense Resistor Required 2% to 87% Duty Cycle at 200kHz tON(MIN) <= 100ns Supports Active Voltage Positioning True Current Mode Control Stable with Ceramic COUT Dual N-Channel MOSFET Synchronous Drive Power Good Output Voltage Monitor Wide VIN Range: 4V to 36V ±1% 0.8V Reference Adjustable Current Limit Adjustable Switching Frequency Forced Continuous Control Pin Programmable Soft-Start Output Overvoltage Protection Optional Short-Circuit Shutdown Timer Micropower Shutdown: IQ < 30µA Available in 28-Lead Narrow SSOP Package Typical Application

Applications Power Supplies for Pentium® Processors Notebook Computers and Servers Packaging

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