A6985F datasheet(42/77 Pages) STMICROELECTRONICS

Part #	A6985F

Description	38 V 500 mA synchronous step-down switching regulator

PDF	77 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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42 / 77 page

Closing the loop

A6985F

42/77

DocID027738 Rev 2

Laplace transformer of the leading network:

Equation 30

where:

Equation 31

6.4

Total loop gain

In summary, the open loop gain can be expressed as:

Equation 32

Example 1

A6985F3V3 with VIN = 12 V and ROUT = 6.6

Selecting L = 4.7µH, COUT = 10 µF and ESR = 1 m, RC= 110 k, CC= 68 pF,

CP = 1.2 pF (please refer to Example 2), the gain and phase bode diagrams are plotted

respectively in Figure 30 and Figure 31.

Equation 33

GDIV s



R1 R2

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

1s R1 CR1





R1 R2



R1 R2

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



CR1







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



 R

CR1



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



R1 R



R1 R2

-------------------- CR1



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

fZ fp





GDIV s

 G

CO s

 A

0 s





112kHz

phase margin

A6985F Datasheet(PDF) 42 Page - STMicroelectronics

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