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ADP1821ARQZ-R7 数据表(PDF) 17 Page - Analog Devices

部件名 ADP1821ARQZ-R7
功能描述  Step-Down DC-to-DC Controller
PDF  24 Pages
Scroll/Zoom Zoom In 100%  Zoom Out
制造商  AD [Analog Devices]
网页  http://www.analog.com
标志 AD - Analog Devices

ADP1821ARQZ-R7 数据表(HTML) 17 Page - Analog Devices

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ADP1821
Rev. B | Page 17 of 24
From K, the frequency of the added zeros, fZ, is below crossover
for Type II by
K
f
f
CO
Z =
(33)
Similarly, the frequency of the added poles, fP, should be
previous crossover by for Type II
fP = fCOK
(34)
Select RTOP between 1 k and 10 k. A good starting value is 2 k.
Next, calculate RBOT as
FB
OUT
TOP
FB
BOT
V
V
R
V
R
−
=
(35)
V
6
.
0
V
6
.
0
−
×
=
OUT
TOP
BOT
V
R
R
(36)
Calculate the compensator gain needed at crossover to achieve
0 dB total system gain:
AT = AMOD + AFILTER + ACOMP
(37)
0 dB = AMOD + AFILTER + ACOMP
(38)
ACOMP
= 0 dB − AMOD − AFILTER
(39)
Calculate the value of RZ to achieve that gain
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
×
=
TOP
Z
COMP
R
R
A
log
20
(40)
⎟
⎠
⎞
⎜
⎝
⎛
×
=
20
10
COMP
A
TOP
Z
R
R
(41)
Calculate the integrator cap value to place the compensation
zero at the desired frequency using the following equation:
Z
Z
I
f
R
π
C
2
1
=
(42)
Calculate the capacitor value for the high frequency pole by
P
Z
HF
f
R
π
C
2
1
=
(43)
Type III Compensator
0V
VRAMP
G
(dB)
PHASE
–270°
–90°
fZ
fP
CHF
CI
RZ
CFF
RTOP
RBOT
FROM
VOUT
VREF
EA
COMP
TO PWM
RFF
–1
SLO
PE
–1
SLO
PE
+1
SL
OP
E
Figure 18. Type III Compensation
2
45
2
tan
⎟
⎠
⎞
⎜
⎝
⎛
⎟
⎠
⎞
⎜
⎝
⎛
+
=
B
φ
K
(44)
K
f
f
CO
Z =
(45)
fP = fCO √K
(46)
Select RTOP between 1 k and 10 k. A good starting value is 2 k.
Next, calculate RBOT as
FB
OUT
TOP
FB
BOT
V
V
R
V
R
−
=
(47)
V
6
.
0
V
6
.
0
−
×
=
OUT
TOP
BOT
V
R
R
(48)
Calculate the feedforward capacitor to produce the first
compensator zero
Z
TOP
FF
f
R
π
C
2
1
=
(49)
Calculate the resistor of the feedforward network to provide the
first high frequency compensator pole
P
FF
FF
f
C
π
R
2
1
=
(50)
Calculate the impedance of the feedforward network at the
crossover frequency, as this is required to set the gain of the
compensator.
FF
CO
FF
FF
R
f
C
π
Z
+
=
2
1
(51)



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