Datasheet

LTC3442
15
3442fb
For more information www.linear.com/LTC3442
APPLICATIONS INFORMATION
TYPICAL APPLICATIONS
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. The
unity-gain frequency of the error amplifier with the TypeI
compensation is given by:
f
UG
=
1
2 • π • R1• C
P1
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
POLE1
≅
1
2 • π • 32e
3
• R1• CP1
Hz
(which is extremely close to DC)
f
ZERO1
=
1
2 • π • R
Z
• C
P1
Hz
f
ZERO2
=
1
2 • π • R1• C
Z1
Hz
f
POLE2
=
1
2 • π • R
Z
• C
P2
Hz
where resistance is in ohms and capacitance is in Farads.
1.22V
R1
R2
3442 F07
FB
12
V
C
C
P1
V
OUT
11
–
+
ERROR
AMP
1.22V
R1
R2
3442 F08
FB
12
V
C
C
P1
C
Z1
R
Z
V
OUT
11
C
P2
–
+
ERROR
AMP
Figure 7. Error Amplifier with Type I Compensation Figure 9. Error Amplifier with Type III Compensation
1MHz Li-Ion to 3.3V at 1.2A Converter with
Manual Mode Control (and Peak Current Limit Only)
SW1
V
IN
SHDN/SS
R
LIM
R
T
SGND
SW2
V
OUT
FB
V
C
BURST
PGND
LTC3442
C
IN
10µF
0.01µF
C
IN
: TAIYO YUDEN JMK212BJ106MG
C
OUT
: TAIYO YUDEN JMK325BJ226MM
L1: TDK RLF7030T-3R3M4R
2.5V TO 4.2V
Li-Ion
15k
340k 2.2k
L1
3.3µH
C
OUT
22µF
220pF
V
OUT
3.3V
1.2A
200k
470pF
3442 TA02
+
43.2k
BURST FIXED FREQ
1M