Micrel, Inc.
V IN = 12V, V OUT = 32V
MIC3263
From the small signal block diagram the loop transfer
function is:
F(kH z)
400
500
600
700
800
900
100 0
8.2 μ H
R S LP
2.77 E +05
2.69 E +05
2.61 E +05
2.53 E +05
2.45 E +05
2.37 E +05
2.30 E +05
10 μ H
RSLP
2 . 70E+05
2 . 60E+05
2 . 51E+05
2 .4 1E+05
2 .3 1E+05
2 .2 2E+05
2 .1 2E+05
22 μ H
RSLP
2.24E+05
2.03E+05
1.81E+05
1.60E+05
1.39E+05
1.18E +05
964 51
110 0
120 0
130 0
1400
1500
1600
1700
2.22 E +05
2.14 E +05
2.06 E +05
1.98E+05
1.90E+05
1.82E+05
1.74E+05
2 .0 3E+05
1 .9 3E+05
1 .8 3E+05
1.74E+05
1 .64E+05
1.54E+05
1.45E+05
75231
540 12
327 93
15000
15000
15000
15000
Figure 13. Simplified Voltage Control Loop
Equation 2 :
T(s) = G ea (s) × G VC (s) × H(s)
where:
1800
1.66E+05 1.35E+05
Table 3. RSLC Values
15000
H(s) =
V CRV
V OUT
and
Boost Compensation
G ea m ? Z o II ? R COMP +
Current-mode control simplifies the compensation. In
current mode the double pole created by the output L and
C is reduced to a single pole. The explanation for this is
beyond the scope of this data sheet, but it can be thought
because the inductor current becomes a co nstant current
sou rce and can’t act to change phase.
? ?
(s) = g
Equation 3 :
V OUT ( s )
G vc (s) =
V CONTROL ( s )
? ?
1 ? ?
? ?
sC COMP ? ?
? ?
? 1-
?
2 R
? ?
? 1 ? ? D'R LOAD ? ?
LO AD ?
? ? 1+ sR LOAD C OUT ?
= ? ?? ?
? Ri ? ? 2
? ?
sL
D'
? 2 ?
Figure 12. MIC3263 Current-Mode Loop Diagram
where R LOAD =
V OUT
I OUT
and Ri = Ai × Rcs = 0.4 ? .
A i = 20
R CS = 0.02 ?
A I and R CS are quantities that are internal to the MIC3263.
The equation for G VC (S) is a theoretical model and should
give an approximate idea of where the poles and zeros are
located.
January 2010
20
M9999-012110
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