L6985F datasheet(38/65 Pages) STMICROELECTRONICS

38 / 65 page

Closing the loop

L6985F

38/65

DocID027836 Rev 2

5.2

Error amplifier compensation network

The typical compensation network required to stabilize the system is shown in Figure 28.

Figure 28. Transconductance embedded error amplifier

RC and CC introduce a pole and a zero in the open loop gain. CP does not significantly affect

system stability but it is useful to reduce the noise at the output of the error amplifier.

The transfer function of the error amplifier and its compensation network is:

Equation 24

where Avo = Gm · Ro

The poles of this transfer function are (if Cc >> C0 + CP):

Equation 25

A0 s



AV0 1s Rc Cc







R0 C0 Cp





Rc Cc sR0 Cc R0 C0 Cp





Rc Cc



 1



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

fPLF

 R



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

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