Linear Technology Launches High-Efficiency Dual ±3A Synchronous Buck Regulator
DDR/DDR2/DDR3 standard compliant DDR power termination compliant

August 9, 2011 – Linear Technology Korea (CEO Hong Sa-kwak, www.linear.com ) announced the release of a high-efficiency dual-monolithic synchronous step-down switching regulator (product name: LTC3618) with bus termination voltage generation capabilities for upcoming standard memory applications and DDR/DDR2/DDR3 requiring current sources and sinks. The output of the first step-down regulator provides a high-accuracy VDDQ supply with ±3A output capabilities. An internal resistor divider sets the VTT DDR termination input and the VTTR reference voltage to half the voltage applied to the VDDQIN input, along with output current capabilities of ±3A (sink/source) at VTT and ±10mA at VTTR. The VTT output is capable of operating at a low output of 0.5V to support all DDR standards.

The LTC3618 operates within an input voltage range of 2.25V to 5.5V and provides a high switching frequency of 4MHz, enabling the use of ultra-small external components. Consequently, it offers a small, compact solution footprint for DDR applications requiring ±3A or less current. The internal synchronous top and bottom power switches have RDS(ON) values of 75mΩ and 55mΩ, respectively. This allows the LTC3618 to achieve a high efficiency of 94%, generating less heat than linear regulator solutions, eliminating the need for external catch diodes, and minimizing the number of external components and board area.

The LTC3618 uses a constant frequency, current mode architecture. The switching frequency can be set between 400 kHz and 4 MHz via a single external resistor. This high-frequency performance allows for the use of smaller capacitor values while maintaining low output voltage ripple. Input capacitance and current ripple can be minimized by selecting 0°, 90°, or 180° phase shifts between the two channels. The LTC3618 can be synchronized with an external clock up to 4 MHz for noise-sensitive switching applications. Forced continuous mode operation reduces noise and RF interference. External compensation options enable transient response optimization across a wide range of loads and output capacitors. The device includes an input overvoltage lockout circuit to protect the input supply from back-boosting.

The LTC3618 is available in thermally enhanced 24-pin 4mm x 4mm QFN and TSSOP packages for optimal thermal performance. The device is guaranteed to operate over a range of -40°C to 125°C, and pricing starts at $4.10 per unit for 1,000 units. For more information, please refer to www.linear.com/product/LTC3618 .

Photo Caption: Dual ±3A DDR Switching Regulator for DDR/DDR2/DDR3 and Upcoming Standard Memory

Product Features: LTC3618

• High-efficiency synchronous operation: Up to 94%
• Dual output with ±3A output current function
• Input voltage range 2.25V ~ 5.5V
• ±1% output voltage accuracy
• Low VTT output voltage range of 0.5V
• VTTR = VDDQIN • 0.5, VFB = VTTR
• Shutdown current: <1μA
• Adjustable switching frequency: Up to 4 MHz
• Internal or external compensation
• Selectable 0°/90°/180° phase shift between channels
• Soft start
• Power Good status output
• Low-profile 24-pin 4mm × 4mm QFN & TSSOP package