L6759D datasheet(25/51 Pages) STMICROELECTRONICS

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L6759D

Output voltage positioning

Doc ID 023240 Rev 1

25/51

6.5

Single-phase section - disable

The single-phase section can be disabled by pulling high the SPWM pin. The related

command is rejected.

6.6

Single-phase section - current reading

The single-phase section performs the same differential current reading across DCR as the

multi-phase section. According to Section 6.2, the current that flows from the SCSN pin is

then given by the following equation (see Figure 9):

Equation 7

6.7

Single-phase section - defining load-line

This method introduces a dependence of the output voltage on the load current recovering

part of the drop due to the output capacitor ESR in the load transient. Introducing a depen-

dence of the output voltage on the load current, a static error, proportional to the output cur-

rent, causes the output voltage to vary according to the sensed current.

Figure 9 shows the current sense circuit used to implement the load-line. The current flow-

ing across the inductor DCR is read through RSG. RSG programs a trans-conductance gain

and generates a current ISDROOP proportional to the current delivered by the single-phase

section that is then sourced from the SFB pin with proper gain eventually adjusted by the

PMBus commands. RSFB gives the final gain to program the desired load-line slope

(Figure 8).

The output characteristic vs. load current is then given by:

Equation 8

where RSLL is the resulting load-line resistance implemented by the single-phase section.

The RSFB resistor can be then designed according to RSLL as follows:

Equation 9

6.8

Dynamic VID transition support

The L6759D manages dynamic VID transitions that allow the output voltage of both sections

to modify during normal device operation for power management purposes. OV, UV, and

per-phase OC signals are masked during every DVID transition and they are re-activated

with proper delay to prevent false triggering. Total OC is active even during DVID.

SCSN

DCR

-------------

SOUT

⋅

SDROOP

SOUT

VID

SFB

SDROOP=

VID

SFB

DCR

-------------

SOUT

VID

SLL

SOUT

⋅

–

⋅⋅

–

⋅

–

SFB

SLL

DCR

-------------

⋅

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