L6759D datasheet(22/51 Pages) STMICROELECTRONICS

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Output voltage positioning

L6759D

22/51

Doc ID 023240 Rev 1

Output voltage positioning

Output voltage positioning is performed by selecting the controller operative-mode for the

two sections and by programming the droop function effect (see Figure 8). 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, so implementing the desired load-line effect.

The L6759D 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 8.

Voltage positioning

6.1

Multi-phase section - phase # programming

The multi-phase section implements a flexible 2 to 3 interleaved-phase converter. To pro-

gram the desired number of phases, pull up with a 1 k

Ω resistor to VCC5 the PWMx signal

that is not required to be used.

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. See Figure 2 for details on 2-phase connections.

6.2

Multi-phase section - current reading and current sharing

loop

The L6759D 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 placing of the

sensing element in different locations without affecting the measurement's accuracy. The

Ref. from DAC

COMP

VSEN

FBR

RFB

To VddCORE

(Remote Sense)

RGND

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