L7986TA datasheet(25/43 Pages) STMICROELECTRONICS

No. de pieza	L7986TA

Descripción Electrónicos	3 A step-down switching regulator

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25 / 43 page

L7986TA

Application information

Doc ID 022098 Rev 3

25/43

Figure 13.

Open-loop gain: module Bode diagram

The guidelines for positioning the poles and the zeroes and for calculating the component

values can be summarized as follows:

Choose a value for R1, usually between 1 kΩ and 5 kΩ, in order to have values of C4

and C5 not comparable with parasitic capacitance of the board.

Choose a gain (R4/R1) in order to have the required bandwidth (BW), that means:

Equation 30

where fESR is the ESR zero:

Equation 31

and Vs is the sawtooth amplitude. The voltage feed-forward keeps the ratio Vs/Vin constant.

Calculate C4 by placing the zero one decade below the output filter double pole:

Equation 32

ESR

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

⎝⎠

⎜⎟

⎛⎞

ESR

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

---------

⋅⋅

⋅

ESR

π ESR C

OUT

⋅⋅

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

π R

⋅⋅

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

L7986TA Datasheet(PDF) 25 Page - STMicroelectronics