High Efficiency ±6A Switching Regulator for DDR Termination

Sep 7, 2011 1:02 AM

Linear Technology Corporation introduces the LTC3617, a high efficiency, monolithic synchronous step-down switching regulator, capable of generating a bus termination voltage for DDR/DDR2/DDR3 and future standard memory applications requiring sourcing and sinking of current. An internal resistor divider sets the VTT DDR termination supply and VTTR reference voltages equal to half the voltage applied to the input, with output current capability of ±6A (sinking/sourcing) at VTT and ±10mA at VTTR. The outputs are capable of operation down to 0.5V. The device operates from an input voltage range of 2.25V to 5.5V and allows switching frequencies as high as 4MHz, allowing for very small externals. This creates a small, compact solution footprint that is preferred for laptop computers and graphics card applications, which need ±6A or less for DDR termination. The internal synchronous top and bottom power switches have an RDS(ON) of only 35mOhm and 25mOhm respectively, enabling the LTC3617 to attain efficiencies as high as 93%, eliminating the need for an external catch diode while minimizing external component count and board space.

The LTC3617 utilizes a constant frequency, current-mode architecture. The switching frequency can be set between 300kHz and 4MHz by a single external resistor. This high frequency capability enables use of smaller capacitor values, while maintaining low output voltage ripple. For noise-sensitive switching applications, the LTC3617 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 uses an input overvoltage lockout circuit to protect the input supply from back-boosting.

For optimal thermal performance, the LTC3617 is offered in a thermally enhanced 24-pin 3mm x 5mm QFN package. The device is guaranteed for operation from -40°C to 125°C. 1,000-piece pricing starts at $3.80 for the E grade and $4.20 for the I grade.

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