L6751B datasheet(41/58 Pages) STMICROELECTRONICS

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L6751B

Efficiency optimization

Doc ID 024028 Rev 1

41/58

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 L6751B re-configures itself to

improve overall system efficiency, according to Table 15.

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.

Phase number is reduced by monitoring the voltage level across the IMON pin: the L6751B

reduces the number of working phases according to the strategy defined by the DPM

pinstrapping and/or PMBus (TM) commands received (see Table 11). DPM12 refers to the

current at which the controller changes from 1 to 2 phases. In the same way, DPM23 defines

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

When DPM is enabled, the L6751B 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 an SetVID command that affects the CORE section and when LTB

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

compatible, DPM is re-enabled after proper delay.

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

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

See Section 7.2.1 for guidelines in designing the IMON load indicator.

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 L6751B features a safety mechanism which re-

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

Table 15.

Efficiency optimization

Feature

PS00h

PS01h

DPM

According to pinstrapping

Active. 1Phase/2Phase according to

Iout

VFDE

Active when in single-phase and

DPM enabled

Active when in single-phase

GDC

12 V driving

GDC set to 5 V

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