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Dual Synchronous Step-Down DC/DC Controller with Digital Power System Management

May 6, 2015
Linear Technology Corporation announces the LTC3887, a dual output synchronous step-down DC/DC controller with I²C-based PMBus interface for digital power system management.

Linear Technology Corporation announces the LTC3887, a dual output synchronous step-down DC/DC controller with I²C-based PMBus interface for digital power system management. The LTC3887 differs from the previously released LTC3880 with an enhanced feature set that includes a faster 70ms power-up time, higher output voltage capability and a fast ADC mode that provides an 8ms update rate for one parameter. In addition, the LTC3887 and LTC3880 have a common board footprint. The LTC3887 combines best in class analog switching regulator performance with precision mixed signal data conversion for unsurpassed ease of power system design and management, supported by the LTpowerPlay™ software development system with easy-to-use graphical user interface (GUI).

The LTC3887 enables digital programming and read back for real-time control and monitoring of critical point-of-load converter functions. Programmable control parameters include output voltage, margining and current limits, input and output supervisory limits, power-up sequencing and tracking, switching frequency, and identification and traceability data. On-chip precision data converters and EEPROM allow for the capture and nonvolatile storage of regulator configuration settings and telemetry variables, including input and output voltages and currents, duty cycle, temperature and fault logging.

The LTC3887 can regulate two independent outputs or can be configured for a two phase single output. Up to 6 phases can be interleaved and paralleled for accurate sharing among multiple ICs, minimizing input and output filtering requirements for high current and/or multiple output applications. An integrated amplifier provides true differential remote output voltage sensing, enabling high accuracy regulation, independent of board IR voltage drops. Applications include high current ASIC, FPGA and processor supplies in telecom, datacom, computing and storage markets.

Configurations for the LTC3887 are easily saved to internal EEPROM over the device’s I²C serial interface using Linear Technology’s LTpowerPlay GUI-based development software. With configurations stored on-chip, the controller can power up autonomously without burdening the host processor. Default settings can be optionally configured by external resistor dividers for output voltage, switching frequency, phase and device address. Multiple designs can be easily calibrated and configured in firmware to optimize a single hardware design for a range of applications. The converter loop gain does not change as the power supply parameters are modified, so compensation remains optimized for multiple configurations.

The LTC3887 features high current integrated gate drivers to drive all N-channel power MOSFETs from input voltages ranging from 4.5V to 24V, and it can produce ± 0.50% accurate output voltages from 0.5V to 5.5V with output currents up to 30A per phase over the full operating temperature range. Highest efficiency is achieved by sensing the voltage drop across the output inductor (DCR) to sense current, or an external sense resistor can optionally be used. Programmable DCR temperature compensation cancels the temperature coefficient of the copper inductor to maintain an accurate and constant current limit over a broad temperature range.

The device’s minimum on-time of just 90nsec makes the LTC3887 ideal for compact high frequency/high step-down ratio applications. Accurate timing across multiple chips and event-based sequencing allow the optimization of power-up and power-down of complex, multiple rail systems. Additional features include constant frequency current mode control with cycle-by-cycle current limit, adjustable soft start, a synchronizable switching frequency, and programmable GPIO pins to indicate part status and to provide autonomous recovery from faults.

The LTC3887 is available in a 40-pin 6mm x 6mm QFN packages with an operating junction temperature range from -40°C to 125°C. The 1,000-piece price starts at $5.47 each.


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