參數(shù)資料
型號: LT1576CS8
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: CAP 330UF 16V ELECT TG SMD
中文描述: 3.5 A SWITCHING REGULATOR, 240 kHz SWITCHING FREQ-MAX, PDSO8
封裝: 0.150 INCH, PLASTIC, SOP-8
文件頁數(shù): 20/28頁
文件大小: 290K
代理商: LT1576CS8
20
LT1576/LT1576-5
APPLICATIO
S I
FOR
ATIO
U
the output. Gain is set by the 1.5A/V transconductance of
the LT1576 power section and the effective complex
impedance from output to ground. Gain rolls off smoothly
above the 160Hz pole frequency set by the 100
μ
F output
capacitor. Phase drop is limited to about 85
°
. Phase
recovers and gain levels off at the zero frequency (
16kHz)
set by capacitor ESR (0.1
).
Error amplifier transconductance phase and gain are shown
in Figure 11. The error amplifier can be modeled as a
transconductance of 1000
μ
Mho, with an output imped-
ance of 570k
in parallel with 2.4pF. In all practical
applications, the compensation network from V
C
pin to
ground has a much lower impedance than the output
impedance of the amplifier at frequencies above 200Hz.
W
U
U
This means that the error amplifier characteristics them-
selves do not contribute excess phase shift to the loop, and
the phase/gain characteristics of the error amplifier sec-
tion are completely controlled by the external compensa-
tion network.
In Figure 12, full loop phase/gain characteristics are
shown with a compensation capacitor of 100pF, giving the
error amplifier a pole at 2.8kHz, with phase rolling off to
90
°
and staying there. The overall loop has a gain of 66dB
at low frequency, rolling off to unity-gain at 58kHz. Phase
shows a two-pole characteristic until the ESR of the output
capacitor brings it back above 16kHz. Phase margin is
about 77
°
at unity-gain.
FREQUENCY (Hz)
G
μ
M
P
2000
1500
1000
500
0
–500
200
150
100
50
0
–50
10
1k
10k
1M
100
100k
GAIN
PHASE
R
570k
C
2.4pF
V
C
ERROR AMPLIFIER EQUIVALENT CIRCUIT
R
LOAD
= 50
V
FB
1
×
10
–3
)
(
+
1.21V
V
SW
V
C
LT1576
GND
1576 F09
R1
OUTPUT
ESR
C
F
C
C
R
C
ERROR
AMPLIFIER
FB
R2
C1
CURRENT MODE
POWER STAGE
g
m
= 1.5A/V
+
Figure 10. Response from V
C
Pin to Output
FREQUENCY (Hz)
10
G
P
40
20
0
–20
–40
40
0
–40
–80
–120
100
1k
1576 F07
10k
100k
GAIN
PHASE
V
IN
= 10V
V
OUT
= 5V
I
OUT
= 500mA
Figure 12. Overall Loop Characteristics
FREQUENCY (Hz)
L
L
80
60
40
20
0
–20
180
135
90
45
0
–45
10
1k
10k
1M
1576 F12
100
100k
V
IN
= 10V
V
OUT
= 5V
I
OUT
= 500mA
C
= 100
μ
F
10V, AVX TPS
C
= 100pF
L = 30
μ
H
PHASE
GAIN
Figure 9. Model for Loop Response
Figure 11. Error Amplifier Gain and Phase
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