LTC3425 Linear Technology, LTC3425 Datasheet - Page 20

• Manufacturer Part Number: LTC3425
• Description: 5A 8MHz 4-Phase Synchronous Step-Up DC/DC Converter
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
LTC3425
modulator control to output DC gain, and the error amp
open-loop gain gives the DC gain of the system:
The output filter pole is given by:
where C
The output filter zero is given by:
where R
resistance.
A troublesome feature of the boost regulator topology is
the right half plane zero (RHP), and is given by:
20
G
G
F
F
FILTERPOLE
FILTERZERO
DC
CONTROL
OUT
ESR
G
CONTROLOUTPUT
is the output filter capacitor.
is the output capacitor equivalent series
8
I
OUT
2 • •
•
U
V
•
IN
V
OUT
,
I
OUT
R
G
U
ESR
EA
1
•
•
C
G
OUT
•
EA
C
5 000
,
OUT
•
W
V
V
OUT
REF
U
At heavy loads this gain increase with phase lag can occur
at a relatively low frequency. The loop gain is typically
rolled off before the RHP zero frequency.
The typical error amp compensation is shown in Figure 9.
The equations for the loop dynamics are as follows:
F
F
F
F
which is extremely close to DC
RHPZ
POLE
POLE
ZERO
1
2
1
2 • •
2
2
2
ERROR
AMP
• •
• •
• •
+
V
–
IN
I
100
OUT
R
R
1
2
1
Z
Z
1
e
•
•
1.25V
•
6
C
C
FB
V
L
Figure 9
C
C
C
•
1
2
C
R
C
C
Z
C1
1
w w w . D a t a S h e e t 4 U . c
C
C2
V
OUT
R1
R2
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