L6985F datasheet(39/65 Pages) STMICROELECTRONICS

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DocID027836 Rev 2

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L6985F

Closing the loop

Equation 26

whereas the zero is defined as:

Equation 27

5.3

Voltage divider

The simple voltage divider contribution is:

Equation 28

A small signal capacitor in parallel to the upper resistor (see Figure 29) of the voltage divider

implements a leading network (fzero < fpole), sometimes necessary to improve the system

phase margin.

Figure 29. Leading network example

Laplace transformer of the leading network:

Equation 29

fPHF

 R

C0 Cp





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

 R



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

GDIV s



R1 R2

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

GDIV s



R1 R2

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

1s R1 CR1





R1 R2



R1 R2

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



CR1







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



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