L5987ATR datasheet(26/42 Pages) STMICROELECTRONICS

Il numero della parte	L5987ATR

Spiegazioni elettronici	3 A step-down switching regulator

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Application information

L5987 - L5987A

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6.4.2

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 singularities 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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