L6985F datasheet(36/65 Pages) STMICROELECTRONICS

36 / 65 page

Closing the loop

L6985F

36/65

DocID027836 Rev 2

Closing the loop

Figure 27. Block diagram of the loop

5.1

GCO(s) control to output transfer function

The accurate control to output transfer function for a buck peak current mode converter can

be written as:

Equation 18

where RLOAD represents the load resistance, gCS the equivalent sensing conductance of the

current sense circuitry,

p the single pole introduced by the power stage and z the zero

given by the ESR of the output capacitor.

FH(s) accounts the sampling effect performed by the PWM comparator on the output of the

error amplifier that introduces a double pole at one half of the switching frequency.

GCO s



RLOAD gcs



RLOAD TSW



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

mC 1D

–





0.5

–





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



------







------





---------------------- FH







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