LTC3443 Datasheet, PDF (13/16 Pages) Linear Technology – High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter

APPLICATIO S I FOR ATIO
The output filter zero is given by:
f_{FILTER_ ZERO}
=
2
•
π
1
• R_ESR
• C_OUT
Hz
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_RHPZ
=
V_IN2
2 • π •I_OUT • L• V_OUT
Hz
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_UG
=
2
•
π
•
1
R1•
Hz
CP1
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.
LTC3443
f_POLE1
≈
2
•
π
1
• 32e³
•R1•
Hz
C_P1
Which is extremely close to DC
f_ZERO1 =
1
2 • π •R_Z
Hz
• C_P1
f_ZERO2 =
1
Hz
2 • π •R1 • C_Z1
f_POLE2
=
1
2 • π •R_Z
• C_P2
Hz
ERROR
AMP
1.22V
FB
12
V_C
C_P1
11
V_OUT
R1
R2
3443 F07
Figure 7. Error Amplifier with Type I Compensation
V_OUT
ERROR
AMP
1.22V
FB
12
R1
C_Z1
V_C
R_Z ^CP1
R2
11
C_P2
3443 F08
Figure 8. Error Amplifier with Type III Compensation
sn3443 3443fs
13