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Dual Output PolyPhase Step-Down Controller with Sub-Milliohm DCR Sensing and Digital Power System Management

The LTC3884 is a dual output PolyPhase DC/DC synchronous step-down switching regulator controller with an I2C-based PMBus compliant serial interface. The controller employs a constant-frequency current mode architecture, together with a unique scheme to provide excellent performance for sub-milliohm DCR applications. Programmable loop compensation allows the controller to be compensated digitally. This device is supported by the LTpowerPlay® software development tool with graphical user interface (GUI).

In conjunction with Arrow Electronics Ltd.

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

Switching frequency, channel phasing output voltage, and device address can be programmed both by the digital interface as well as external configuration resistors. Additionally, parameters can be set via the digital interface or stored in EEPROM. Both outputs have independent power good indicators and FAULT function. The LTC3884 can be configured for discontinuous (pulseskipping) mode or continuous inductor current mode.

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 characterization, optimization 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 - an open standard I²C-based digital serial interface protocol. 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 analog control loops, precision mixed-signal circuitry and EEPROM, and is housed in a 7mm x 7mm QFN-48 package.

To evaluate the performance of the LTC3884, the LTpowerPlay GUI is free for download. USB-to-PMBus converter and demo kits are also available. With ±0.5% maximum DC output error over temperature, ±1.5% current read back accuracy, integrated 16-bit Delta-Sigma ADC and EEPROM, the LTC3884 combines best-in-class analog switching regulator performance with precision mixed-signal data acquisition and nonvolatile fault logging. Channels can accurately share current in both steady state and transient conditions. At start-up, output voltages, switching frequency and channel phase angle assignments can be set by pin-strapping resistors or loaded from internal EEPROM. 1,000-piece price is $6.35 each.

For more information, visit www.linear.com/product/LTC3884.

Author
Linear Technology (UK) Limited

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