L6756D

Device description and operation

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Device description and operation

L6756D is a programmable two-to-four phase PWM controller providing complete control

logic and protections for a high performance step-down DC-DC voltage regulator optimized

for advanced microprocessor power supply. The device is a dual-edge asynchronous PWM

simultaneously all the phases allowing to minimize output voltage deviation so minimizing

the system cost by providing the fastest response to a load transition.

Multi-phase buck is the simplest and most cost-effective topology employable to satisfy the

increasing current demand of newer microprocessors and modern high current VRM

modules. It allows distributing equally load and power between the phases using smaller,

cheaper and most common external power MOSFETs and inductors. Moreover, thanks to

the equal phase shift between each phase, the input and output capacitor count results in

being reduced. Phase interleaving causes in fact input rms current and output ripple voltage

reduction and show an effective output switching frequency increase: the 200 kHz

free-Running frequency per phase, externally adjustable through a resistor, results

multiplied on the output by the number of phases.

L6756D permits easy system design by allowing current reading across inductor in fully

differential mode. Also a sense resistor in series to the inductor can be considered to

improve reading precision. The current information read corrects the PWM output in order to

equalize the average current carried by each phase.

The controller includes multiple DACs, selectable through an apposite pin, allowing

compatibility with Intel VR10, VR11 and VR11.1 processors specifications, also performing

D-VID transitions accordingly.

The device is VR11.1 compatible implementing the Imon signal and managing the PSI#

signal to enhance the system performances at low current in low power-states.

Low-side-less start-up allows soft-start over pre-biased output avoiding dangerous current

return through the main inductors as well as negative spike at the load side.

L6756D provides overvoltage protection to protect the load from dangerous over stress

latching immediately by turning ON the lower driver and driving high the FAULT pin.

The device is available in a compact VFQFPN40 with 6x6 mm body package.