LTC3443
13
3443fa
APPLICATIO S I FOR ATIO
WUUU
The output filter zero is given by:
f
RC
Hz
FILTER ZERO
ESR OUT
_
•• •
=
π
1
2
where R
ESR
is the capacitor equivalent series resistance.
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
f
V
ILV
Hz
RHPZ
IN
OUT OUT
=
π
2
2• • • •
The loop gain is typically rolled off before the RHP zero
frequency.
A simple Type I compensation network can be incorpo-
rated to stabilize the loop but at a cost of reduced band-
width and slower transient response. To ensure proper
phase margin, the loop requires to be crossed over a
decade before the LC double pole.
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
f
RCP
Hz
UG
=
π
1
211•• •
Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a
higher bandwidth, Type III compensation is required. Two
zeros are required to compensate for the double-pole
response.
Figure 7. Error Amplifier with Type I Compensation
Figure 8. Error Amplifier with Type III Compensation
1.22V
R1
R2
3443 F07
FB
12
V
C
C
P1
V
OUT
11
–
+
ERROR
AMP
1.22V
R1
R2
3443 F08
FB
12
V
C
C
P1
C
Z1
R
Z
V
OUT
11
C
P2
–
+
ERROR
AMP
f
eRC
Hz
Which is extremely close to DC
f
RC
Hz
f
RC
Hz
f
RC
Hz
POLE
P
ZERO
ZP
ZERO
Z
POLE
ZP
1
3
1
1
1
2
1
2
2
1
232 1
1
2
1
21
1
2
≈
π
=
π
=
π
=
π
•• • •
•• •
•• •
•• •
