38V dual PMBus DC/DC controller with current mode control

October 30, 2015 // By Graham Prophet
LTC3884 is a dual output current mode synchronous step-down DC/DC controller with programmable loop compensation and I²C-based PMBus interface. This device enables the use of very low DC resistance (DCR) power inductors (0.3 milliOhms) by enhancing the signal-to-noise ratio of the current sense signal to maximise converter efficiency and increase power density.

The LTC3884 operates over an input voltage range of 4.5V to 38V and produces output voltages up to 5.5V. Up to 6 phases can be paralleled and clocked out-of-phase to minimise input and output filtering. When both outputs are paralleled, the LTC3884 provides less than ±5% current mismatch between phases. Alternatively, the LTC3884 can be used with the LTC3874 phase extender, suiting it for high current requirements up to 240A. Onboard differential amplifiers provide true remote output voltage sensing of both outputs. Applications include power distribution, redundant (n+1) supplies, FPGA, ASIC and processor power.

The device has a selectable fixed operating frequency from 200 kHz to 1 MHz or it can be synchronised to an external clock. 1.1Ω onboard all N-channel gate drivers minimise MOSFET switching losses. The LTC3884’s adjustable and precise current limit threshold can be configured for very low sense voltages from 10 mV to 30 mV, further reducing power loss. Features include input current sensing, two power-good output signals, programmable soft-start and programmable fault recovery method.

The LTC3884 is supported by the LTpowerPlay software development tool with graphical user interface (GUI). Its serial I²C-based interface enables system designers and remote operators to command and supervise a system’s power condition and consumption. The capability to digitally change power supply parameters reduces time-to-market and down time, eliminating what would typically require physical hardware, circuit or system bill-of-material modifications. The LTC3884 simplifies system characterisation, optimisation and data mining during prototyping, deployment and field operation.

In addition to delivering power to a point-of-load, the LTC3884 features configurability and telemetry monitoring of power and power management parameters over PMBus. The LTC3884’s 2-wire serial interface enables outputs to be margined, tuned and ramped up and down at programmable slew rates with sequenced delay times. Input and output voltages, along with input and output currents and temperature are readable. The device is comprised of fast analogue control loops, precision mixed-signal circuitry and EEPROM, and