Datasheet

f
CROSS_MAX
=
f
SW
5
f
CROSS_MAX
=
f
SW
4 x Q
1 + 4 x Q
2
-1
x
( )
Z
P_EA
= Z
Z_ESR
Z
Z_EA
= Z
P_LF
when
&
f
CROSS
<
Z
P_HF
2 x S x 10
& &
f
CROSS
<
Z
P_ESR
2 x S x 10
Z
P_EA
= Z
Z_ESR
Z
Z_EA
= Z
P_LF
&
when
2 x ' x R
S
x R
FB2
x A
S
x C
OUT
R
COMP
f
CROSS
=
2 x ' x R
S
x R
FB2
x A
S
x (C
OUT1
+ C
OUT2
)
R
COMP
f
CROSS
=
Z
Z_EA
= Z
P_LF
when
Z
P_EA
= Z
Z_ESR
Z
Z_EA
= Z
P_LF
&
when
T(s) =
s
A
M
x A
FB
x
Z
Z_ESR
1 +
s
s
(1 + )
Z
P_EA
x
(1 + )
Z
P_ESR
x
(1 + + )
s
s
Z
P_HF
s
2
Z
n
2
T(s)
A
M
x A
FB
s
=
T(s) = A
M
x A
FB
x
Z
Z_EA
s
(1 + )
Z
P_EA
1 +
s
s x
s
(1 + )
Z
P_LF
x
Z
Z_ESR
1 +
s
T(s) = A
M
x A
FB
x
x
Z
Z_ESR
1 +
s
s
(1 + )
Z
P_LF
x
(1 + )
Z
P_ESR
x
(1 + + )
s
s
Z
P_HF
s
2
Z
n
2
s
(1 + )
Z
P_EA
s x
Z
Z_EA
1 +
s
LM25117
LM25117-Q1
SNVS714E –APRIL 2011–REVISED MARCH 2013 www.ti.com
Table 1. LM25117 Frequency Analysis Formulas
(1)
(continued)
SIMPLE FORMULA COMPREHENSIVE FORMULA*
Open-Loop
Response
Crossover
Frequency
(Open Loop
Bandwidth)
Maximum
Crossover
Frequency
The frequency at which 45° phase shift occurs in modulator phase
characteristics.
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