High Power Dual Output Multiphase Step-Down DC/DC Controller with Differential Output Voltage Sensing, Tracking and PLL

Nov 10 2009 -MILPITAS, CA
  • Linear Technology Corporation introduces the LTC3855, a dual output high efficiency (up to 95%) synchronous step-down DC/DC controller with multiphase operation, differential output voltage sensing and integrated phase-lock loop (PLL) synchronization. Up to 12 phases can be paralleled and clocked out of phase to minimize input and output filtering requirements for high current applications (up to 200A). The differential amplifier provides true remote output voltage sensing of both the positive and negative terminals, enabling high accuracy regulation where IR losses occur through vias, trace runs and interconnects. Applications include high current ASIC and FPGA supplies, power distribution buses, high power audio amplifiers and network servers.


    The LTC3855 operates with all N-channel MOSFETs from input voltages ranging from 4.5V to 38V, and it can produce ±0.75% accurate output voltages from 0.6V to 12.5V. The output current is sensed by monitoring the voltage drop across the output inductor (DCR) or by using a sense resistor. Programmable DCR temperature compensation maintains an accurate and constant over current limit over a broad temperature range. The on-board 1.1Ω gate driver minimizes MOSFET switching losses and allows the use of multiple MOSFETs connected in parallel. A fixed operating frequency can be programmed from 250kHz to 770kHz or can be synchronized to an external clock with its internal PLL. The device’s minimum on-time of just 90ns makes the LTC3855 ideal for high step-down ratio applications.


    Tracking and sequencing functions allow the optimization of power-up and power-down of multiple power supplies. Additional features include current mode control, an on-board LDO for IC power, programmable soft start, two power good signals and external VCC control.


    The LTC3855 is available in 38-lead SSOP or 40-lead 6mm × 6mm QFN packages. The LTC3855E operates from –40ºC to 85ºC, with the 1000-piece price starting at $3.18. The LTC3855I Industrial grade version operates from –40ºC to 125ºC, with a 1,000-piece price starting at $3.59 each. Both versions are available from stock. For more information, visit www.linear.com.


    Summary of Features: LTC3855


    • Multiphase Operation – Up to 12 Phases
    • High Efficiency – Up to 95%
    • High Power – Up to 200A
    • Wide Input Voltage Range from 4.5V to 38V
    • Output Voltages Ranging from 0.6V to 12.5V ±0.75% Accuracy
    • RSENSE or DCR Current Sensing
    • Programmable DCR Temperature Compensation
    • Powerful 1.1Ω Dual N-Channel MOSFET Gate Driver
    • True Differential Amplifiers for Remote Output Voltage Sensing
    • Output Voltage Tracking or Programmable Soft Start
    • Phase-Lockable Fixed Frequency from 250kHz to 770kHz
    • Current Mode Control for Accurate & Easy Current Sharing

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