LTC3443 Linear Technology, LTC3443 Datasheet - Page 13

• Manufacturer Part Number: LTC3443
• Description: High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
The output filter zero is given by:
where R
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
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:
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.
f
f
f
FILTER ZERO
UG
RHPZ
=
ESR
2
=
_
• •
2 • •
is the capacitor equivalent series resistance.
π
π
R CP
1
=
1
I
OUT
•
U
2
V
• •
IN
π
2
• •
1
L V
Hz
U
R
ESR
1
OUT
•
C
Hz
OUT
W
Hz
U
f
Which is extremely close to DC
f
f
f
POLE
ZERO
ZERO
POLE
Figure 8. Error Amplifier with Type III Compensation
Figure 7. Error Amplifier with Type I Compensation
1
2
2
1
≈
=
=
=
2
2
2
2
ERROR
• •
AMP
• •
• •
• •
π
π
π
π
+
–
ERROR
32
AMP
R
R
R
1
1
1
Z
1
Z
e
1
+
–
3
•
•
•
V
C
FB
12
11
C
C
•
C
Z
1.22V
P
R
P
1
1
2
1
Hz
Hz
•
FB
12
V
11
Hz
C
C
1.22V
R
P
Z
1
C
w w w . D a t a S h e e t 4 U . c o m
P2
C
Hz
P1
C
P1
LTC3443
V
3443 F08
OUT
V
OUT
R1
R2
3443 F07
R1
R2
sn3443 3443fs
13
C
Z1