L6751 datasheet(30/59 Pages) STMICROELECTRONICS

30 / 59 page

Output voltage positioning

L6751

30/59

Doc ID 023992 Rev 1

Output voltage positioning

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

Table 6, 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 L6751 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 pro-

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

required, according to Table 7.

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 L6751 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 induc-

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

ment to be placed in different locations without affecting measurement accuracy. The trans-

Ref. from DAC

COMP

VSEN

FBR

RFB

To VddCORE

(Remote Sense)

RGND

AM14814v1

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