Datasheet

   
   
SLUS419C − AUGUST 1999 − REVISED NOVEMBER 2001
23
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TYPICAL APPLICATION
control loop
Figure 12 shows the control block diagram for the typical application shown in Figure 9. G
C
(s) is the
compensation network’s transfer function (TF), G
OPTO
(s) is the opto-isolator TF, G
CO
(s) is the control-to-output
TF, and H(s) is the divider TF. The following equations can be used to estimate the frequency response of each
gain block, where f
OPTO_pole
is the frequency, where the optoisolator is −3 dB from its dc operating point, and
V
REF_TL431
is the reference voltage of the TL431 shunt regulator. R
LOAD
represents the typical load impedance
for the design.
G
OPTO
(s) +
R13
R36
1
1 )
s
2p f
OPTO_pole
G
C
(s) +
s R35 C14 ) 1
s C14 R31
(
1 )
(
s R35 C15
))
R13
R36
1
1 )
s
2p f
OPTO_pole
H(s) +
R27
R27 ) R31
+
V
VREF_TL431
V
OUT
G
CO
(s) +
V
OUT
V
C
+
R
LOAD
R
SENSE2
N
P
N
s
ǒ
1 )
ǒ
s C
OUT
ESR
Ǔ
Ǔ
ǒ
1 )
ǒ
s C
OUT
R
LOAD
Ǔ
Ǔ
Σ
V
REF_TL431
G
C
(s)
G
CO
(s)
V
BOOST
V
OUT
H(s)
V
C
Figure 12. UCC38500 Control Block
(38)
(39)
(40)
(41)