MAX1808EUB+ Maxim Integrated, MAX1808EUB+ Datasheet - Page 16

• Manufacturer Part Number: MAX1808EUB+
• Description: Current & Power Monitors & Regulators
• Manufacturer: Maxim Integrated

Solving for C
3) Place a high-frequency pole at f
When using a low-ESR tantalum or ceramic type, the
ESR-induced zero frequency is usually above the tar-
geted zero crossover frequency (f
pensation. Type III compensation provides three poles
and two zeros at the following frequencies:
Two midband zeros (f
complex poles introduced by the LC filter:
f
nulling DC output voltage errors:
Low-Cost, Small, 4.5V to 28V Wide Operating
Range, DC-DC Synchronous Buck Controller
MAX15026
16
Figure 3. Type II Compensation Network
P1
attenuate the ripple at the switching frequency, f
and calculate C
introduces a pole at zero frequency (integrator) for
V
OUT
R
R
2
1
F
:
Type III Compensation Network
C
C
V
f
f
REF
F
Z
Z
CF
1
2
=
CF
f
=
P
=
=
2
2
2
using the following equation:
π
2
π
π
=
Z1
π
×
×
f
×
P1
2
×
R
R
π
R
and f
F
C
F
1
g
F
= 0
×
M
I
×
×
×
×
R
1
1
1
f
1
PO
f
I
(
SW
C
R
×
Z2
F
1
C
×
O
C
+
−
R
) cancel the pair of
F
I
F
0 75
). Use Type III com-
R
C
.
P1
1
I
(See Figure 4)
F
)
= 0.5 x f
COMP
C
SW
CF
SW
(to
)
Depending on the location of the ESR zero (f
f
the high-frequency output ripple:
f
Place the zeros and poles so the phase margin peaks
around f
Ensure that R
R
phase shift is introduced to the response making the
loop unstable.
Use the following compensation procedure:
1) With R
So:
2) The gain of the modulator (GAIN
Figure 4. Type III Compensation Network
P2
P3
2
C
R
, and R
I
I
the pulse-width modulator, LC filter, feedback
divider, and associated circuitry at the crossover
frequency is:
attenuates the high-frequency output ripple.
to cancel f
G N
AI
O
R
R
F
MOD
.
1
2
I
V
≥ 10kΩ, place the first zero (f
OUT
is greater than 1/g
F
f
ZO
Z
>>2/g
=
1
f
P
G N
V
, or to provide additional attenuation of
=
3
RAMP
AI
V
=
2
V
IN
REF
π
M
2
MOD
×
π
and the parallel resistance of R
R
×
×
1
F
R
(
=
2
×
F
π
C
V
×
RAMP
×
R
1
F
V
C
C
g
F
IN
f
M
O
=
F
F
C
M
)
CF
0 8
×
+
2
. Otherwise, a 180°
.
C
C
×
×
CF
CF
×
(
L
1
MOD
2π
OUT
f
C
PO
Z1
F
) at 0.8 x f
Maxim Integrated
), comprises
×
C
OUT
ZO
), use
COMP
PO
1
.
,