PM8903 datasheet(20/34 Pages) STMICROELECTRONICS

Part #	PM8903

Description	3 A step-down monolithic switching regulator

PDF	34 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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20 / 34 page

Application information

PM8903

20/34

Doc ID 022748 Rev 1

stability, it should not exceed FSW/2π. To achieve a good phase margin, the control loop gain

must cross the 0 dB axis with -20 dB/decade slope.

As an example,

Figure 12 shows an asymptotic bode plot of a type III compensation.

Figure 12.

Example of type III compensation

The open loop converter singularities are:

The compensation network singularity frequencies are:

π LC

OUT

⋅

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

ESR

π C

OUT

ESR

⋅⋅

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

π R

⋅⋅

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

π R

() C

⋅⋅

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

π R

⋅

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

⎝⎠

⎛⎞

⋅⋅

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

π R

⋅⋅

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

PM8903 Datasheet(PDF) 20 Page - STMicroelectronics