L6756D datasheet(33/36 Pages) STMICROELECTRONICS

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L6756D

System control loop compensation

33/36

Sensitivity of the load transient detector and the gain of the LTB ramp can be programmed in

order to control precisely both the undershoot and the ring-back.

●

Detector design. RLTB - CLTB is design according to the output voltage deviation dVOUT

which is desired the controller to be sensitive as follow:

●

Gain design. Through the LTBGAIN pin it is possible to modify the slope of the LTB

Ramp in order to modulate the entity of the LTB response once the LT has been

detected. In fact, the response depends on the board design and its parasites requiring

different actions from the controller.

Leaving the LTBGAIN pin floating, the maximum pulse-width is programmed. The slope

of the LTB ramp will be equal to 1/2 of the OSC ramp slope.

Connecting RLTBGAIN to GND, the LTB Ramp slope can be modified as follow:

Where ILTBGAIN is the current sunk from LTBGAIN pin and IOSC is the OSC current

(20

μA plus the current coming from the OSC pin).

LTB Technology® design tips.

–

Descries RLTB to increase the system sensitivity making the system sensitive to

smaller dVOUT.

–

Increase CLTB to increase the system sensitivity making the system sensitive to

higher dV/dt.

–

Increase RLTBGAIN to increase the width of the LTB pulse.

LTB

OUT

μA

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

LTB

πNR

LTB

⋅⋅

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

LTBRamp

Slope

OSC

Slope

LTBGAIN

OSC

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

⎝⎠

⎛⎞

⋅

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