Synchronous step-down DC/DC controller uses nonlinear control for tight output voltage regulation

August 11, 2011 // By Paul Buckley
Linear Technology Corporation has introduced a fixed frequency synchronous step-down DC/DC controller with nonlinear control, differential output voltage sensing and clock synchronization. Nonlinear control minimizes the output voltage excursion during load transient events by increasing the operating frequency, allowing the LTC3867 to recover from a large load step in only a few cycles.

The feature reduces the maximum deviation from nominal by up to 50% compared to traditional controllers. The LTC3867's 4 V to 38 V input range encompasses a wide variety of applications including most intermediate bus voltages. Strong onboard N-channel MOSFET gate drivers allow the use of high power external MOSFETs for high load current, up to 25 A. The output voltage range is 0.6 V to 14 V, making the LTC3867 ideal for telecom, datacom, automotive and industrial applications.     

The LTC3867's differential amplifier provides true remote output voltage sensing of both the positive and negative terminals, enabling high accuracy regulation independent of IR losses (up to ±300 mV) in trace runs, vias and interconnects. A low 65 ns minimum on-time allows for a high step-down ratio power supply at high frequency operation.      

The operating frequency is selectable from 200 kHz to 1.2 MHz or can be synchronized to an external clock. The output current is monitored by sensing the voltage drop across the output inductor (DCR) for highest efficiency or by using a sense resistor. Additional features include DCR temperature compensation, an onboard bias voltage LDO, soft-start or tracking, adjustable current limit, soft recovery from an output overcurrent condition, overvoltage protection, external VCC control and ±1% reference voltage accuracy over a -40 to 125°C operating junction temperature range.

The LTC3867 is available in a thermally enhanced 4 mm x 4m m QFN-24 package. The 1,000-piece price starts at $2.76 each.      

More information about the LTC3867 synchronous step-down DC/DC controller at