Datasheet

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K
3
+ tan
ǒ
Q
LEAD
Ǔ
) tan
ǒ
Q
LEAD
Ǔ
) 1
Ǹ
(dimensionless)
(34)
f
Z3
+
f
C
K
3
(Hz)
(35)
f
P3
+ f
C
K
3
(Hz)
(36)
K
LF
+
K
COMP(co)
K
3
(dimensionless)
(37)
R
2
+ K
LF
R
1
(W)
(38)
K
HF
+ K
COMP(co)
K
3
(dimensionless)
(39)
R
3
+
R
1
R
2
K
HF
R
1
* R
2
(W)
(40)
C
3
+
1
2 p R
3
f
P3
(F)
(41)
TPS40100
SLUS601–MAY 2005
APPLICATION INFORMATION (continued)
Select the required extra phase lead beyond the Type II compensation to obtain the required phase margin and
calculate the required multiple for the additional pole and zero:
where
•Θ
LEAD
is the required extra phase lead to be generated by the addition of the extra pole and zero
• K
3
is the multiplier applied to f
C
to get the new pole and zero locations
The locations of f
Z3
and f
P3
are:
where
• K
3
is the multiplier applied to f
C
to get the new pole and zero locations
• f
Z3
is the zero created by the addition of R
3
and C
3
• f
P3
is the pole created by the addition of R
3
and C
3
The required gain, K
COMP(co)
, from the compensator at f
C
, is the same as for the Type II compensation, found in
Equation 30. The gain K
LF
(see Figure 9) is found by:
R
2
can then be found:
The high-frequency gain is:
Now:
The remaining pole and zero are located a decade above and below f
C
as before. Equation 31 and Equation 32
canbeusedtosolveforC
1
and C
2
as before.
19