L6722 datasheet(17/34 Pages) STMICROELECTRONICS

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L6722

7 Output voltage positioning

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Output voltage positioning

Output voltage positioning is performed by programming the external resistor divider and by

correctly designing Droop Function and Offset to the reference (Optional). The output voltage is

then driven by the following relationship (See Figure 7):

Both DROOP and OFFSET function can be disabled: see Section 7.1 and Section 7.2 for

details.

L6722 embeds a Remote Sense Buffer to sense remotely the regulated voltage without any

additional external components. In this way, the output voltage programmed is regulated

between the remote buffer inputs compensating for board and connector losses. The device

senses the output voltage remotely through the pins FBR and FBG (FBR is for the regulated

voltage sense while FBG is for the ground sense) and reports this voltage internally at VSEN

pin with unity gain eliminating the errors. Keeping the FBR and FBG traces parallel and

guarded by a power plane results in common mode coupling for any picked-up noise.

When regulating output voltages higher than the reference, it is possible to insert a resistor

divider between FBR, FBG and the regulated voltage as reported in Figure 7. In this case it is

important for the external divider to have a value negligible with respect to the remote buffer

impedance that has 64k resistors.

Figure 7.

Voltage positioning

7.1

Offset and margining-mode (optional)

Positive / negative offset can be added to the programmed reference by connecting proper

network resistor between the REF_OUT and REF_IN pins. In this way is possible to manage

margining-mode by adding small offsets (positive or negative) to the regulated voltage, in order

to test the loading-circuitry in different operative conditions to check for the reliability of the

system designed.

Referring to Figure 8, a constant current (IOS=12µA) is sourced from the REF_IN pin as soon

as the device is enabled. By correctly designing ROS1 and ROS2, positive and negative offset

may be added to the reference voltage according to the status of the control signals M1 and

M2. Different operating conditions can be then considered:

OUT

Ref

()

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

⋅

To Vout

(Remote Sense)

Ref

COMP

VSEN

64k

FBR

FBG

64k

RFB

REF_IN

REF_OUT

ROS

COS

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