L6751C datasheet(28/57 Pages) STMICROELECTRONICS

28 / 57 page

Output voltage positioning

L6751C

28/57

DocID025037 Rev 1

Output voltage positioning

Output voltage positioning is performed by selecting the controller operative-mode, as per

Table 6 on page 20, for the two sections and by programming the droop function effect (see

Figure 6). The controller reads the current delivered by each section by monitoring the

voltage drop across the DCR inductors. The current (IDROOP / ISDROOP) sourced from the

FB / SFB pins, directly proportional to the read current, causes the related section output

voltage to vary according to the external RFB / RSFB resistor, therefore implementing the

desired load-line effect.

The L6751C embeds a dual remote-sense buffer to sense remotely the regulated voltage of

each section without any additional external components. In this way, the output voltage

programmed is regulated compensating for board and socket losses. Keeping the sense

traces parallel and guarded by a power plane results in common mode coupling for any

picked-up noise.

Figure 6. Voltage positioning

6.1

Multi-phase section - phase # programming

The multi-phase section implements a flexible 3 to 6 interleaved-phase converter. To proram

the desired number of phases, simply short to VCC5 the PWMx signal that is not required,

according to Table 7 on page 20.

Caution:

For the disabled phase(s), the current reading pins need to be properly connected to avoid

errors in current-sharing and voltage-positioning: CSxP needs to be connected to the

regulated output voltage while CSxN needs to be connected to CSxP through the same RG

resistor used for the active phases.

6.2

Multi-phase section - current reading and current sharing

loop

The L6751C embeds a flexible, fully-differential current sense circuitry that is able to read

across inductor parasitic resistance or across a sense resistor placed in series to the

inductor element. The fully-differential current reading rejects noise and allows the sensing

element to be placed in different locations without affecting measurement accuracy. The

Ref. from DAC

COMP

VSEN

FBR

RFB

To VddCORE

(Remote Sense)

RGND

AM14814v1

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