参数资料
型号: LTC3634EUFD#TRPBF
厂商: LINEAR TECHNOLOGY CORP
元件分类: 稳压器
英文描述: 5.5 A DUAL SWITCHING CONTROLLER, 4600 kHz SWITCHING FREQ-MAX, PQCC28
封装: 4 X 5 MM, LEAD FREE, PLASTIC, MO-220, QFN-28
文件页数: 8/28页
文件大小: 359K
代理商: LTC3634EUFD#TRPBF
LTC3634
16
3634f
applicaTions inForMaTion
Choosing Compensation Components
Loop compensation is a complicated subject and Applica-
tion Note 76 is recommended reading for a full discussion
on maximizing loop bandwidth in a current mode switch-
ing regulator. This section will provide a quick method on
choosing proper components to compensate the LTC3634
regulators.
Figure 4 shows the recommended components to be con-
nected to the ITH pin, and Figure 5 shows an approximate
bode plot of the buck regulator loop using these compo-
nents. It is assumed that the major poles in the system
(the output capacitor pole and the error amplifier output
pole) are located at a frequency lower than the crossover
frequency.
Figure 4. Compensation and Filtering Components
Figure 5. Bode Plot of Regulator Loop
P
LOG ()
C
Z
3634 F05
–1
0dB
|H(s)|
–2
The first step is to choose the crossover frequency fC.
Higher crossover frequencies will result in a faster loop
transient response; however, in order to avoid higher or-
der loop dynamics from the switching power stage, it is
recommended that fC not exceed one-tenth the switching
frequency (fSW).
Once fC is chosen, the value of RCOMP that sets this cross-
overfrequencycanbecalculatedbythefollowingequation:
RCOMP =
2
π fC COUT
gm(EA) gm(MOD)
VOUT
VFBREG
where gm(EA) is the error amplifier transconductance
(see the Electrical Characteristics section), and gm(MOD)
is the modulator transconductance (the transfer function
from ITH voltage to current comparator threshold). For
the LTC3634, this transconductance is nominally 7Ω–1.
Once RCOMP is determined, CCOMP can be chosen to set
the zero frequency (fZ):
fZ =
1
2
π CCOMP RCOMP
For 90° of phase margin, fZ should be chosen to be less
than one-tenth of fC.
Since the ITH node is sensitive to noise coupling, a small
bypass capacitor (CBYP) may be used to filter out board
noise. However, this cap contributes a pole at fP and may
introduce some phase loss at the crossover frequency:
fP =
1
2
π CBYP RCOMP
For best results, fP should be set high enough such that
phase margin is not significantly affected.
If necessary, a capacitor CF (as shown in Figure 3) may
be used to add some phase lead.
LTC3634
CBYP
RCOMP
CCOMP
3634 F04
ITH
SGND
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