L5983 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

L5983

2A step-down switching regulator

STMicroelectronics 

Application informations

The transfer function on the LC filter is given by:

Equation 13

1 + ------------s-------------

GLC(s)

=

-----------------------------2----π----⋅---f--z---E---S----R--------------------

1

+

-------------s---------------

2π ⋅ Q ⋅ fLC

+

⎛

⎝

2----π-----s⋅---f--L---C--⎠⎞

2

where:

Equation 14

fLC

=

-----------------------------------1------------------------------------ ,

2π ⋅

L ⋅ COUT ⋅

1 + --E----S----R----

ROUT

fzESR

=

---------------------1----------------------

2π ⋅ ESR ⋅ COUT

L5983

Equation 15

Q

=

-----R----O----U----T----⋅---L-----⋅---C-----O----U----T----⋅---(--R-----O----U----T----+-----E----S-----R-----)

L + COUT ⋅ ROUT ⋅ E SR

,

ROUT

=

V-----O----U---T--

IOUT

As seen in Chapter 4.3 two different kind of network can compensate the loop. In the two

following paragraph the guidelines to select the Type II and Type III compensation network

are illustrated.

Figure 9. Error amplifier, PWM modulator and LC output filter

VCC

VREF

FB

VS

E/A

COMP

PWM

GPW0

OUT

L

ESR

GLC

COUT

5.4.1

Type III compensation network

The methodology to stabilize the loop consists of placing two zeros to compensate the effect

of the LC double pole, so increasing phase margin; then to place one pole in the origin to

minimize the dc error on regulated output voltage; finally to place other poles far away the

zero dB frequency.

19/37

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