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參數資料
| 型號： | UC2577TD-ADJ |
| 英文描述： | Current-Mode SMPS Controller |
| 中文描述： | 電流模式開關電源控制器 |
| 文件頁數： | 6/8頁 |
| 文件大?。?/td> | 208K |
| 代理商： | UC2577TD-ADJ |
UC2577-ADJ
3. Compensation Network (R
C
, C
C
) and Output
Capacitor (C
OUT
) Selection
The compensation network consists of resistor R
C
and
capacitor C
C
which form a simple pole-zero network and
stabilize the regulator. The values of R
C
and C
C
depend
upon the voltage gain of the regulator, I
LOADmax
, the in-
ductor L, and output capacitance C
OUT
. A procedure to
calculate and select the values for R
C
, C
C,
and C
OUT
which ensures stability is described below. It should be
noted, however, that this may not result in optimum com-
pensation. To guarantee optimum compensation a stand-
ard procedure for testing loop stability is recommended,
such as measuring V
OUT
transient responses to pulsing
I
LOAD
.
A. Calculate the maximum value for R
C
.
R
C
≤
750
I
LOADmax
V
OUT
2
V
INmin
2
Select a resistor less than or equal to this value, not to
exceed 3k
.
B. Calculate the minimum value for C
OUT
using the fol-
lowing two equations.
C
OUT
≥
0.19
L
R
C
I
LOADmax
V
INmin
V
OUT
and
C
OUT
≥
V
INmin
R
C
(
V
INmin
+
(
3.74
10
5
L
))
487,800
V
OUT
3
The larger of these two values is the minimum value that
ensures stability.
C. Calculate the minimum value of C
C
.
C
C
≥
58.5
V
OUT
2
C
OUT
R
C
2
V
INmin
The compensation capacitor is also used in the soft start
function of the regulator. When the input voltage is ap-
plied to the part, the switch duty cycle is increased slowly
at a rate defined by the compensation capacitor and the
soft start current, thus eliminating high input currents.
Without the soft start circuitry, the switch duty cycle would
instantly rise to about 90% and draw large currents from
the input supply. For proper soft starting, the value for C
C
should be equal or greater than 0.22
μ
F.
Figure 6 lists several types of aluminum electrolytic ca-
pacitors which could be used for the output filter. Use the
following parameters to select the capacitor.
Working Voltage (WVDC):Choose a capacitor with a
working voltage at least 20% higher than the regulator
output voltage.
Ripple Current:This is the maximum RMS value of cur-
rent that charges the capacitor during each switching cy-
cle. For step-up and flyback regulators, the formula for
ripple current is:
I
RIPPLErms
=
I
LOADmax
D
max
1
D
max
Choose a capacitor that is rated at least 50% higher than
this value at 52kHz.
Equivalent Series Resistance (ESR):This is the primary
cause of output ripple voltage, and it also affects the val-
ues of R
C
and C
C
needed to stabilize the regulator. As a
result, the preceding calculations for C
C
and R
C
are only
valid if the ESR does not exceed the maximum value
specified by the following equations.
I
RIPPLE
(
P
P
)
and
≤
8.7
10
3
V
IN
ESR
≤
0.01
15V
I
LOADmax
where
I
RIPPLE
(
P
P
)
=
1.15
I
LOADmax
1
D
max
Select a capacitor with an ESR, at 52kHz, that is less
than or equal to the lower value calculated. Most electro-
lytic capacitors specify ESR at 120kHz which is 15% to
30% higher than at 52kHz. Also, note that ESR increases
by a factor of 2 when operating at
20
°
C.
In general, low values of ESR are achieved by using
large value capacitors (C
≥
470
μ
F), and capacitors with
high WVDC, or by paralleling smaller value capacitors.
Inductor
Code
L47
L68
L100
L150
L220
L330
L470
L680
H150
H220
H330
H470
H680
H1000
H1500
H2200
Manufacturer’s Part Number
AIE
Pulse
415 - 0932
PE - 53112
415 - 0931
PE - 92114
415 - 0930
PE - 92108
415 - 0953
PE - 53113
415 - 0922
PE - 52626
415 - 0926
PE - 52627
415 - 0927
PE - 53114
415 - 0928
PE - 52629
415 - 0936
PE - 53115
430 - 0636
PE - 53116
430 - 0635
PE - 53117
430 - 0634
PE - 53118
415 - 0935
PE - 53119
415 - 0934
PE - 53120
415 - 0933
PE - 53121
415 - 0945
PE - 53122
Renco
RL2442
RL2443
RL2444
RL1954
RL1953
RL1952
RL1951
RL1950
RL2445
RL2446
RL2447
RL1961
RL1960
RL1959
RL1958
RL2448
AIE Magnetics, Div. Vernitron Corp.,
(813)347-2181
2801 72nd Street North, St. Petersburg, FL 33710
Pulse Engineering,
(619)674-8100
12220 World Trade Drive, San Diego, CA 92128
Renco Electronics, Inc.,
(516)586-5566
60 Jeffryn Blvd. East, Deer Park, NY 11729
Figure 5. Table of Standardized Inductors and
Manufacturer’s Part Numbers
APPLICATIONS INFORMATION (cont.)
6
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