Dual step-down DC/DC controller update adds PWM signals

August 18, 2015 // By Graham Prophet
LTC3887-1 is a dual output synchronous step-down DC/DC controller with I²C-based PMBus interface for digital power system management. The LTC3887-1 differs from the previously released LTC3887 (introduced March 2015) by providing a three-state PWM signal, enabling the use of DrMOS, power blocks or similar power stages.

The LTC3887-1’s feature set includes a 70msec power-up time and a fast ADC mode that provides an 8 msec update rate for one parameter. The part regulates two independent outputs or can be configured for a 2-phase single output from 0.5V to 5.5V. Up to 6 phases can be interleaved and paralleled for accurate sharing among multiple ICs, minimising input and output filtering requirements for high current or multiple output applications. An integrated amplifier provides true differential remote output voltage sensing, enabling high accuracy regulation, independent of board IR voltage drops.

The controller operates over an input voltage ranging from 4.5V to 24V, and it produces ±0.50% accurate output voltages from 0.5V to 5.5V with output currents up to 40A 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 be optionally 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.

Accurate timing across multiple chips and event-based sequencing enable the optimisation 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 synchronisable switching frequency, and programmable GPIO pins to indicate part status and to provide autonomous recovery from faults.

The LTC3887-1 combines analogue switching regulator performance with precision mixed signal data conversion, supported by the GUI-based LTpowerPlay power development system. It provides 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,