Linear Tech Dual Synchronous Buck Regulator for DDR Power & Termination Complies with DDR/DDR2/DDR3 Standards
Linear Technology Corp. introduced the LTC3618, a dual monolithic synchronous step-down switching regulator, 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 operates from an input voltage range of 2.25 to 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 75 and 55mΩ, respectively. This enables the LTC3618 to attain efficiencies as high as 94%, eliminating the need for an external catch diode and minimizing external component count and board space, as well as generating far less heat than linear regulator solutions.
The LTC3618 utilizes a constant frequency, current-mode architecture. The switching frequency can be set between 400kHz and 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 compensation 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 to 125°C. 1,000-piece pricing starts at $4.10 each.
