L6740L datasheet(23/44 Pages) STMICROELECTRONICS

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L6740L

Output voltage positioning

23/44

Output voltage positioning

Output voltage positioning is performed by selecting the controller operative-mode (SVI, PVI

and V_FIX) and by programming the Droop Function and Offset to the reference of both the

sections (See Figure 9). The controller reads the current delivered by each Section by

monitoring the voltage drop across the Low-Side MOSFET for NB Section or DCR Inductors

for CORE Section. The current (IDROOP / IDROOP_NB) sourced from the DROOP /

NB_DROOP pin, directly proportional to the read current, causes the related section output

voltage to vary according to the external RFB / RFB_NB resistor so implementing the desired

load-line effect. The current (IOS / IOS_NB) programmed through the OS / NB_OS pins is

sunk from the FB / NB_FB pins causing the output voltage to be offset according to the

resistance RFB / RFB_NB connected.

L6740L 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.

Both DROOP and OFFSET function can be disabled: see Section 6.3 and Section 6.4 for

details about CORE Section and Section 6.6 and Section 6.7 for details about NB Section.

In case DROOP effect is not desired, the current information sourced from the DROOP pin

may be used to implement a Load Indicator as reported in Section 6.3 and Section 6.6.

Figure 9.

Voltage positioning

1.2V

ROS

CORE_REFERENCE

COMP

VSEN

FBG

RFB

To VDD_CORE

(Remote Sense)

DROOP

CORE Protection

Monitor

from DAC...

1.2V

ROS_NB

NB_OS

NB_REFERENCE

NB_FB

NB_COMP

NB_VSEN

NB_FBG

RF_NB

CF_NB

RFB_NB

To VDD_NB

(Remote Sense)

NB_DROOP

NB Protection

Monitor

from DAC...

RFB_COMP

RFB_COMP_NB

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