Datasheet

MAX1953/MAX1954/MAX1957
Low-Cost, High-Frequency, Current-Mode PWM
Buck Controller
20 ______________________________________________________________________________________
VV
IA
CF
LH
R
gS
AA
R
g
AR
S
f MHz
R
V
I
V
A
f
C
Rf
OUT
OUT MAX
OUT
ESR
mEA
VCS
DS ON
mc
VCS DS ON
S
LOAD
OUT
OUT MAX
pMOD
OUT
LOAD
=
=
=
=
=
=
=
=
=
×
=
=
===
=
××
×
25
3
20
1
0 0025
110
63
0 013
1
12 21
1
25
3
0 833
1
2
.
.
.
.
.
.
.
()
()
()
()
µ
µ
µ
π
Ω
Ω
Ω
SS
LOAD
S
ESR
zESR
OUT ESR
C
L
RfL
RF
MHz H
MHz H
kHz
f
CR F
MHz
Pick the crossover frequency f
×
()
×
()
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
+
=
××
××
+×
()
+
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
=
=
××
=
××
=
)
.
.
.
.
.
.
()
1
220
0 833 1 1
0 833 1 1
0 0025
17 42
1
2
1
2 20 0025
32
π µ
µ
µ
ππµ
Ω
Ω
Ω
Ω
atat the switching frequency f We choose kHz f so C
is not needed The power ulator gain at f is
Gg
RfL
RfL
f
f
S
MHz H
MHz H
kHz
kHz
S zESR F
C
MOD f mc
LOAD S
LOAD S
pMOD
C
C
<<
=×
××
×
×=×
××
+×
×=
1 5 100
12 21
0 833 1 1
0 833 1 1
17 42
100
0
/ ( ). ,
. mod :
()
()
.
.( )
.( )
.
.
()
Ω
Ω
µ
µ
967967
25
110 0 8 937
33
25
3
11
25
3
11
20
33
then
R
V
gVG
V
SV
k
And
C
V
I
fL
V
I
fL
C
R
V
A
MHz H
V
A
MHz H
F
C
OUT
mEA FB MOD f
C
OUT
OUT MAX
S
OUT
OUT MAX
S
OUT
C
C
:
.
..
:
()
()
.
()
.
()
()
()
()
=
××
=
××
≈
=
××
+×
×=
××
+×
×
µ
µ
µ
µ
Ω
kk
pF
Ω
≈ 270
Figure 6. Numerical Example to Calculate R
C
and C
C
Values of the Typical Operating Circuit of Figure 1 (MAX1953)