L5981 datasheet(22/37 Pages) STMICROELECTRONICS

Teilenummer	L5981

Bauteilbeschribung	1 A step-down switching regulator

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Hersteller	STMICROELECTRONICS [STMicroelectronics]

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Application information

L5981

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5.4.2

Type II compensation network

If the equivalent series resistance (ESR) of the output capacitor introduces a zero with a

frequency lower than the desired bandwidth (that is: 2

π * ESR * COUT > 1 / BW), this zero

helps stabilize the loop. Electrolytic capacitors show not negligible ESR (> 30 m

Ω), so with

this kind of output capacitor the type II network combined with the zero of the ESR allows

stabilizing the loop.

In Figure 13 the type II network is shown.

Figure 13.

Type II compensation network

The singularity of the network are:

In Figure 14 the Bode diagram of the PWM and LC filter transfer function (GPW0 · GLC(f))

and the open loop gain (GLOOP(f) = GPW0 · GLC(f) · GTYPEII(f)) are drawn.

π R

⋅⋅

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

π R

⋅

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

⋅⋅

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L5981 Datenblatt(PDF) 22 Page - STMicroelectronics