L5983_08 datasheet(20/37 Pages) STMICROELECTRONICS

20 / 37 page

Application information

L5983

20/37

Equation 19

Calculate C5 by placing the second pole at four times the system bandwidth (BW):

Equation 20

Set also the first pole at four times the system bandwidth and also the second zero at

the output filter double pole:

Equation 21

The suggested maximum system bandwidth is equals to the switching frequency divided by

3.5 (FSW/3.5), anyway lower than 100 kHz if the FSW is set higher than 500 kHz.

For example with VOUT = 3.3 V, VIN = 12 V, IO = 1.5 A, L = 22 μH, COUT = 22 μF,

ESR < 1 m

Ω, the type III compensation network is:

In Figure 12 is shown the module and phase of the open loop gain. The bandwidth is about

77 kHz and the phase margin is 47°.

π R

⋅⋅

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

π R

4BW

⋅

–

⋅⋅⋅

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

4BW

⋅

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

–

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

π R

4BW

⋅⋅ ⋅

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

4.99k

1.1k

120

4.99k

4.7nF

10nF

68pF

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