Power Electronics / Power Management


Step-down DC/DC controller

8 February 2012 Power Electronics / Power Management

Linear Technology’s new LTC3839 is a high-frequency, controlled on-time, single-output, dual phase synchronous step-down DC/DC controller that can achieve up to 95% efficiency with a 25 A output when operating at 2 MHz. The operating frequency is selectable from 200 kHz to 2 MHz or can be synchronised to an external clock.

A low 30 ns minimum on-time allows for a high step-down ratio at very high operating frequencies. The controlled on-time, valley current-mode architecture and ‘detect transient release’ feature provide a very fast transient response by increasing operating frequency during a transient event, enabling the output voltage to recover in only a few clock cycles. Up to 12 phases can be paralleled and clocked out of phase for high-current applications (up to 250 A).

The LTC3839 operates over a 4,5 V to 38 V input voltage range, encompassing 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 output currents up to 50 A, at output voltages ranging from 0,6 V to 5,5 V, making the device well suited for point-of-load requirements.

The IC’s differential amplifier provides true remote output voltage sensing of both the positive and negative terminals, enabling high-accuracy regulation independent of PCB IR losses (up to ±500 mV). The output current is monitored by sensing the voltage drop across the output inductor (DCR) for highest efficiency or by using a sense resistor for extra precision. Additional features include an onboard bias voltage LDO, soft-start or tracking, adjustable current limit, over-voltage protection, current limit foldback and external VCC control.

The LTC3839 offers high total regulation accuracy and is specified to account for all error sources including line, load and differential sensing. Total output voltage accuracy is ±0,25% at 25°C, ±0,67% from 0°C to 85°C, and ±1% maximum DC error over the full -40°C to 125°C operating junction temperature range.



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