L6712 datasheet(15/27 Pages) STMICROELECTRONICS

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L6712A L6712

in the regulated output voltage, the "native" offset of the amplifier must be multiplied by the term

KOS = [1+(1/RA_Gain)] because a voltage generator insisting on the non-inverting input represents

the offset.

If remote sense is not required, it is enough connecting RFB directly to the regulated voltage: VSEN be-

comes not connected and still senses the output voltage through the remote amplifier. In this case the use

of the external resistors R1 and R2 becomes optional and the Remote Sense Amplifier can simply be con-

nected as a "buffer" to keep VSEN at the regulated voltage (See figure 7). Avoiding use of Remote Am-

plifier saves its offset in the accuracy calculation but doesn't allow remote sensing.

INTEGRATED DROOP FUNCTION (Optional)

Droop function realizes dependence between the regulated voltage and the delivered current (Load Reg-

ulation). In this way, a part of the drop due to the output capacitor ESR in the load transient is recovered.

As shown in Figure 8, the ESR drop is present in any case, but using the droop function the total deviation

of the output voltage is minimized.

Connecting DROOP pin and FB pin together, forces a current IDROOP, proportional to the output current,

into the feedback resistor RFB implementing the load regulation dependence. If RA_Gain is the Remote

Amplifier gain, the Output Characteristic is then given by the following relationship (when droop enabled):

with a remote amplifier gain of 1/2, the regulated output voltage results in being doubled.

The Droop current is equal to 50

µA at nominal full load and 70µA at the OC intervention threshold, so the

maximum output voltage deviation is equal to:

Droop function is provided only for positive load; if negative load is applied, and then IINFOx<0, no current

is sunk from the FB pin. The device regulates at the voltage programmed by the VID.

If this effect is not desired, shorting DROOP pin to SGND, the device regulates as a Voltage Mode Buck

converter.

Figure 8. Load Transient response (Left) and DROOP pin connection (Right).

MONITOR AND PROTECTIONS

The device monitors through pin VSEN the regulated voltage in order to build the PGOOD signal and man-

age the OVP / UVP conditions.

■ PGOOD. Power good output is forced low if the voltage sensed by VSEN is not within ±12% (Typ.) of

the programmed value (RA_Gain=1). It is an open drain output and it is enabled only after the soft start

OUT

RA_Gain

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

VID

FB IDROOP

⋅

–

()

⋅

RA_Gain

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

VID

SENSE

---------------------- I

OUT

⋅⋅

–





⋅

∆V

FU L L

PO S ITIVE

–

LO AD

–

RA_Gain

------------------------- R

⋅

µA

∆V

O C

IN TE R VEN TIO N

–

RA_Gain

------------------------- R

⋅

µA

⋅

–

⋅

–

MAX

MIN

NOM

ESR DROP

DROOP PIN = GND

DROOP PIN = FB PIN

Reference

DROOP

REMOTE

AMPLIFIER

ERROR

AMPLIFIER

DROOP

COMP

VSEN

FBG

FBR

Remote

Ground

Remote

OUT

Short to GND if DROOP function is not

implemented (Classic Voltage Mode).

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