LTC3532_15 Datasheet, PDF (13/16 Pages) Linear Technology – Micropower Synchronous Buck-Boost DC/DC Converter

LTC3532
APPLICATIO S I FOR ATIO
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 using Type I compensation, the loop must
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:
1
f_UG = _{2 • π • R1• CP1} Hz
referring to Figure 7.
Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a higher
bandwidth, Type III compensation is required, providing
two zeros to compensate for the double-pole response of
the output filter. Referring to Figure 8, the location of the
poles and zeros are given by:
f_{P O L E1}
≅
2
•
π
•
1
32e³
•
R1•
CP1
Hz
(which is extremely close to DC)
1
f_ZERO1 = _{2 • π • RZ • CP1} Hz
f_{Z E R O2}
=
2
•
π
1
• R1•
C_Z1
Hz
f_{P O L E 2}
=
2•
π
1
• R_Z
• C_P2
Hz
where resistance is in ohms and capacitance is in far-
ads.
ERROR
AMP
1.22V
FB
9
V_C
C_P1
10
V_OUT
R1
R2
3532 F07
Figure 7. Error Amplifier with Type l Compensation
ERROR
AMP
V_OUT
1.22V
FB
9
R1
C_Z1
V_C
R_Z ^CP1
R2
10
C_P2
3532 F08
Figure 8. Error Amplifier with Type lll Compensation
3532fc
13