ST1S40 datasheet(11/29 Pages) STMICROELECTRONICS

11 / 29 page

DocID17928 Rev 5

11/29

ST1S40

Functional description

Figure 5. Small signal model for the error amplifier

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

system stability and can be neglected.

So GEA(s) results:

Equation 8

where GEA= Gm · Ro

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

Equation 9

Equation 10

whereas the zero is defined as:

Equation 11

The embedded compensation network is RC = 70 k, CC = 195 pF while CP and CO can be

considered as negligible. The error amplifier output resistance is 240 M

so the relevant

singularities are:

Equation 12

GEA s



GEA0 1s

Rc Cc







2 R

C0 Cp

 R

c Cc

sR0 Cc



R0 C0 Cp

 R

c Cc



 1







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

fP LF

 R

0 Cc





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

fP HF

 R

C0 Cp







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

 R

c Cc





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

11 6 kHz



fP LF

34 Hz



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