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Switching regulator offers ㊣3A VDDQ supply

Posted: 11 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:buck regulator? dual monolithic? standard memory?

Linear Technology Corp. has rolled out the LTC3618, a high-efficiency dual monolithic synchronous step-down switching regulator. The LTC3618 is capable of generating the supply voltage and the bus termination voltage for DDR/DDR2/DDR3 and future standard memory applications requiring both sourcing and sinking of current.

The output of the first step-down regulator offers a high accuracy VDDQ supply capable of ㊣3A output. An internal resistor divider sets the VTT DDR termination supply and VTTR reference voltages equal to half the voltage applied to the VDDQIN input, with output current capability of ㊣3A (sinking/sourcing) at VTT and ㊣10mA at VTTR. The VTT output is capable of operation down to 0.5V to support all DDR standards.


The LTC3618 can be synchronized to an external clock up to 4MHz.

The LTC3618 operates from an input voltage range of 2.25每5.5V and allows switching frequencies as high as 4MHz, enabling the use of very small external components. This creates a small, compact solution footprint that is preferred for DDR applications requiring ㊣3A or less current. The internal synchronous top and bottom power switches have an RDS(on) of only 75m? and 55m?, respectively. According to Linear Technology, this enables the LTC3618 to attain efficiencies as high as 94 percent, eliminating the need for an external catch diode and minimizing external component count and board space, as well as generating less heat than linear regulator solutions.

The LTC3618 utilizes a constant frequency, current-mode architecture. The switching frequency can be set between 400kHz每4MHz by a single external resistor. This high frequency capability allows use of smaller capacitor values, while maintaining low output voltage ripple. 0∼, 90∼ or 180∼ of phase shift between the two channels can be selected to minimize input capacitance and current ripple. For noise-sensitive switching applications, the LTC3618 can be synchronized to an external clock up to 4MHz. Forced continuous mode operation helps reduce noise and RF interference. Optional external compenzation allows optimization of transient response over a wide range of loads and output capacitors. The device includes an input overvoltage lockout circuit to protect the input supply from back-boosting.

For optimal thermal performance, the LTC3618 is offered in 24-pin thermally enhanced 4 x 4mm QFN and TSSOP packages. The device is guaranteed for operation from -40∼C每125∼C. 1,000-piece pricing starts at $4.10 each.

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