L6759D datasheet(34/51 Pages) STMICROELECTRONICS

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Efficiency optimization

L6759D

34/51

Doc ID 023240 Rev 1

Efficiency optimization

As per VR12 specifications, the SVI master may define different power states for the VR

controller. This is performed by SetPS commands. The L6759D re-configures itself to

improve overall system efficiency according to Table 10.

9.1

Dynamic phase management (DPM)

Dynamic phase management allows the number of working phases to be adjusted

according to the delivered current still maintaining the benefits of the multi-phase regulation.

The phase number is reduced by monitoring the voltage level across the IMON pin: the

L6759D reduces the number of working phases according to the strategy defined by the pin-

strapping configured and/or PMBus(TM) commands received (see Table 6 ). DPM12 refers

to the current at which the controller changes from 1 to 2 phases while DPM23 defines the

current at which the controller changes from 2 to 3 phases.

When DPM is enabled, the L6759D starts monitoring the IMON voltage for phase number

modification after VR_RDY has transition high: the soft-start is then implemented in

interleaving mode with all the available phases enabled.

DPM is reset in case of a SetVID command that affects the multi-phase section and when

LTB Technology™ detects a load transient. After being reset, if the voltage across IMON is

compatible, DPM is re-enabled after a proper delay.

Delay in the intervention of DPM can be adjusted by properly sizing the filer across the

IMON pin. Increasing the capacitance results in increased delay in the DPM intervention.

Note:

During load transients with light slope, the filtering of IMON may result too slow for the IC to

set the correct number of phases required for the current effectively loading the system (LTB

does not trigger in case of light slopes). The L6759D features a safety mechanism which re-

enables phases that were switched off by comparing ILIM and IMON pin voltage. In fact, the

ILIM pin is lightly filtered in order to perform a fast reaction of OC protection while IMON is

heavily filtered to perform the correct averaging of the information. While working

continuously in DPM, the device compares the information of IMON and ILIM: ILIM voltage is

divided into N steps with a width of VOCP/(2*N) (where VOCP = 2.5 V and N the number of

stuffed phases). If the DPM phase number resulting from IMON is not coherent with the step

in which ILIM stays, the phase number is increased accordingly.The mechanism is active

only to increase the phase number which is reduced again by DPM.

Table 10.

Efficiency optimization

Feature

PS00h

PS01h

DPM

According to pin-strapping and

PMBus(TM).

Active. 1Phase/2Phase according to

Iout.

VFDE

Active when in single-phase and

DPM enabled.

Active when in single-phase

GDC

According to pin-strapping and

PMBus(TM).

GDC set to 5 V.

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