L5985 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L5985' PDF : 36 Pages View PDF
L5985
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
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
VREF
FB
VS
E/A
COMP
PWM
GPW0
VCC
OUT
L
ESR
GLC
COUT
18/36
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