Synchronous buck regulator complies with ddr/ddr2/ddr3 standards
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Linear Technology has announced a new dual monolithic synchronous step down switching regulator, which it says 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 is designed to offer 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 is operable from an input voltage range of 2.25 to 5.5V and allows switching frequencies up to 4MHz. The internal synchronous top and bottom power switches have an RDS (on) of 75 and 55mOhm, respectively. This is said to enable the regulator to attain efficiencies up to 94% and eliminate the need for an external catch diode.
The LTC3618 utilises a constant frequency, current mode architecture. Linear says the switching frequency can be set between 400kHz and 4MHz by a single external resistor. For noise sensitive switching applications, the device can be synchronised to an external clock up to 4MHz. Forced continuous mode operation has been implemented to reduce noise and rf interference. 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 a 24pin, thermally enhanced 4 x 4mm QFN and TSSOP package. The device is guaranteed for operation from between -40 and 125°C.
