參數(shù)資料
型號(hào): LTC1553LCG
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: Advanced,Self-Calibrating, Precision, Dual Operational Amplifier 8-SOIC -40 to 125
中文描述: SWITCHING CONTROLLER, 350 kHz SWITCHING FREQ-MAX, PDSO20
封裝: 0.209 INCH, PLASTIC, SSOP-20
文件頁數(shù): 16/20頁
文件大?。?/td> 370K
代理商: LTC1553LCG
16
LTC1553L
Feedback Loop Compensation
The LTC1553L voltage feedback loop is compensated at
the COMP pin, attached to the output node of the internal
g
m
error amplifier. The feedback loop can generally be
compensated properly with an RC + C network from COMP
to GND as shown in Figure 8a.
Loop stability is affected by the values of the inductor,
output capacitor, output capacitor ESR, error amplifier
transconductance and error amplifier compensation net-
work. The inductor and the output capacitor create a
double pole at the frequency:
1
2
π√
(L
O
)(C
OUT
)
The ESR of the output capacitor forms a zero at the
frequency:
f
LC
=
f
ESR
=
1
2
π
(ESR)(C
OUT
)
The compensation network at the error amplifier output is
to provide enough phase margin at the 0dB crossover
frequency for the overall closed-loop transfer function.
The zero and pole from the compensation network are:
f
Z
=
1
2
π
(R
C
)(C
C
)
and
f
P
=
1
2
π
(R
C
)(C1)
respectively.
Figure 8b shows the Bode plot of the overall transfer
function.
The compensation value used in this design is based on
the following criteria: f
SW
= 12f
CO
, f
Z
= f
LC
and f
P
= 5f
CO
. At
the closed-loop frequency f
CO
, the attenuation due the LC
filter and the input resistor divider is compensated by the
gain of the PWM modulator and the gain of the error
amplifier (g
mERR
)(R
C
). Although a mathematical approach
to frequency compensation can be used, the added
complication of input and/or output filters, unknown ca-
pacitor ESR, and gross operating point changes with input
voltage, load current variations, all suggest a more prac-
tical empirical method. This can be done by injecting a
transient current at the load and using an RC network box
to iterate toward the final compensation values, or by
obtaining the optimum loop response using a network
analyzer to find the actual loop poles and zeros.
APPLICATIO
S I
FOR
ATIO
U
W
U
U
Figure 8a. Compensation Pin Hook-Up
1553L F08a
DAC
LTC1553L
SENSE
COMP
10
R
C
C
C
C1
+
ERR
6
Figure 8b. Bode Plot of the LTC1553L Overall Transfer Function
–20dB/DECADE
L
f
P
f
Z
f
CO
f
ESR
FREQUENCY
1553L F08b
f
= LTC1553L SWITCHING
FREQUENCY
f
CO
= CLOSED-LOOP CROSSOVER
FREQUENCY
f
LC
Table 6. Suggested Compensation Network for 5V Input
Application Using Multiple Paralleled 330
μ
F AVX TPS Output
Capacitors
L
O
(
μ
H)
1
990
1
1980
1
4950
2.7
990
2.7
1980
2.7
4950
5.6
990
5.6
1980
5.6
4950
C
O
(
μ
F)
R
C
(k
)
1.8
3.6
9.1
5.1
10
24
10
20
51
C
C
(
μ
F)
0.022
0.01
0.01
0.01
0.01
0.0047
0.01
0.0047
0.0036
C1 (pF)
680
330
120
220
120
47
120
56
22
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