LTC3534 Linear Dimensions Semiconductor, LTC3534 Datasheet - Page 14

• Manufacturer Part Number: LTC3534
• Description: 500mA Synchronous Buck-Boost DC
• Manufacturer: Linear Dimensions Semiconductor

www.DataSheet4U.com
LTC3534
The output fi lter zero is given by:
where R
output capacitor.
A troublesome feature in boost mode is the right-half plane
zero (RHP), given by:
The loop gain is typically rolled off before the RHP zero
frequency.
A simple Type I compensation network can be incorporated
to stabilize the loop, but at a cost of reduced bandwidth and
slower transient response. To ensure proper phase margin
using Type I compensation, the loop must be crossed over
a decade before the LC double pole. Referring to Figure
5, the unity-gain frequency of the error amplifi er utilizing
Type I compensation is given by:
APPLICATIONS INFORMATION
14
f
f
f
RHPZ
FILTER _ ZERO
UG
Figure 5. Error Amplifi er with Type I Compensation
=
ESR
2 • π • R1• C
=
2 • π •I
is the equivalent series resistance of the
1
=
ERROR
OUT
AMP
2 • π • R
V
P1
IN
+
–
• L1• V
2
Hz
ESR
1
FB
V
15
14
OUT
C
1V
• C
OUT
C
Hz
P1
Hz
V
11
OUT
R1
R2
3534 F05
Most applications demand an improved transient response
to allow a smaller output fi lter capacitor. To achieve a higher
bandwidth, Type III compensation is required, providing
two zeros to compensate for the double-pole response of
the output fi lter. Referring to Figure 6, the location of the
poles and zeros are given by:
where resistance is in Ohms and capacitance is in Far-
ads.
(which is extremely close to DC)
f
f
f
f
POLE1
POLE2
ZERO1
ZERO2
Figure 6. Error Amplifi er with Type III Compensation
≅
=
=
=
2 • π • 5 × 10
2 • π • R
2 • π • R
2 • π • R1• C
ERROR
AMP
+
–
1
1
1
Z
Z
• C
• C
1
V
FB
15
14
Z1
3
P1
P2
C
1V
• R1• C
Hz
Hz
Hz
R
Z
C
P1
P2
C
V
Hz
P1
11
OUT
C
Z1
3534 F06
R1
R2
3534f