High efficiency dual ±3-A synchronous buck regulator complies with DDR/DDR2/DDR3 standards
The output of the first step-down regulator offers a high accuracy V DDQ supply capable of ±3 A output. An internal resistor divider sets the V TT DDR termination supply and V TTR reference voltages equal to half the voltage applied to the V DDQIN input, with output current capability of ±3 A (sinking/sourcing) at V TT and ±10 mA at V TTR . The V TT output is capable of operation down to 0.5 V to support all DDR standards.
The LTC3618 operates from an input voltage range of 2.25 V to 5.5 V and allows switching frequencies as high as 4 MHz, enabling the use of small external components. This creates a small, compact solution footprint that is preferred for DDR applications requiring ±3 A or less current. The internal synchronous top and bottom power switches have an R DS(ON) of only 75 mOhm and 55 mOhm, 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 400 kHz and 4 MHz 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 4 MHz. 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 mm x 4 mm QFN and TSSOP packages. The device is guaranteed for operation from -40 to 125°C. 1,000-piece pricing starts at $4.10 each.
More information about the LTC3618 dual monolithic synchronous step-down switching regulator at www.linear.com/product/LTC3618.
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