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參數(shù)資料
| 型號(hào)： | ISL6557ACBZ-T |
| 廠商： | INTERSIL CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | Multi-Phase PWM Controller for Core-Voltage Regulation |
| 中文描述： | SWITCHING CONTROLLER, 1500 kHz SWITCHING FREQ-MAX, PDSO24 |
| 封裝： | LEAD FREE, PLASTIC, MS-013AD, SOIC-24 |
| 文件頁(yè)數(shù)： | 15/19頁(yè) |
| 文件大?。?/td> | 540K |
| 代理商： | ISL6557ACBZ-T |
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15
The feedback resistor, R
FB
, has already been chosen as out-
lined in
Load-Line Regulation Resistor
. Select a target band-
width for the compensated system, f
0
. The target bandwidth
must be large enough to assure adequate transient perfor-
mance, but smaller than 1/3 of the per-channel switching fre-
quency. The values of the compensation components
depend on the relationships of f
0
to the L-C pole frequency
and the ESR zero frequency. For each of the three cases
defined below, there is a separate set of equations for the
compensation components.
In Equations 20, L is the per-channel filter inductance
divided by the number of active channels; C is the sum total
of all output capacitors; ESR is the equivalent-series
resistance of the bulk output-filter capacitance; and V
PP
is
the peak-to-peak sawtooth signal amplitude as described in
Figure 5 and
Electrical Specifications
.
Once selected, the compensation values in Equations 20
assure a stable converter with reasonable transient perfor-
mance. In most cases, transient performance can be
improved by making adjustments to R
C
. Slowly increase the
value of R
C
while observing the transient performance on an
oscilloscope until no further improvement is noted. Normally,
C
C
will not need adjustment. Keep the value of C
C
from
Equations 20 unless some performance issue is noted.
The optional capacitor C
2
, is sometimes needed to bypass
noise away from the PWM comparator (see Figure 5). Keep
a position available for C
2
, and be prepared to install a high-
frequency capacitor of between 22pF and 150pF in case any
jitter problem is noted.
COMPENSATION WITHOUT LOAD-LINE REGULATION
The non load-line regulated converter is accurately modeled
as a voltage-mode regulator with two poles at the L-C
resonant frequency and a zero at the ESR frequency. A type
III controller, as shown in Figure 13, provides the necessary
compensation.
The first step is to choose the desired bandwidth, f
0
, of the
compensated system. Choose a frequency high enough to
assure adequate transient performance but not higher than
1/3 of the switching frequency. The type-III compensator has
an extra high-frequency pole, f
HF
. This pole can be used for
added noise rejection or to assure adequate attenuation at
the error-amplifier high-order pole and zero frequencies. A
good general r
u
le is to chose f
HF
= 1
0f
0
, but it can be higher
if desired. Choosing f
HF
to be lower than 1
0
f
0
can cause
problems with too much phase shift below the system
bandwidth.
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
Equations 21, R
FB
is selected arbitrarily. The remaining
compensation components are then selected according to
Equations 21.
2
π
LC
-------------------
f
0
>
R
C
R
FB
2
π
f
V
LC
IN
0.75V
PP
FB
f
0
-----------------------------------
=
C
C
------------------------------------
=
Case 1:
2
π
LC
-------------------
f
0
)
-----------------------------
<
≤
R
C
R
FB
V
2
π
0.75 V
IN
0.75V
)
f
V
PP
R
FB
LC
2
2
--------------------------------------------
=
C
C
2
π
(
------------------------------------------------------------
=
Case 2:
(EQ. 20)
f
0
)
-----------------------------
>
R
C
R
FB
2
π
f
V
L
IN
)
-----------------------------------------
=
C
C
0.75V
ESR
2
π
V
PP
R
FB
f
0
L
-------------------------------------------------
=
Case 3:
FIGURE 13. COMPENSATION CIRCUIT FOR ISL6557A BASED
CONVERTER WITHOUT LOAD-LINE
REGULATION
I
COMP
C
C
R
C
R
FB
FB
IOUT
VDIFF
-
+
V
DROOP
C
2
C
1
R
1
R
1
R
FB
(
LC
–
C ESR
)
----------------------------------------
=
C
1
FB
)
------------–
=
C
2
0.75V
2
π
(
)
f
0
f
HF
LCR
FB
V
PP
------------------------------------------------------------------
=
(EQ. 21)
R
C
R
V
2
π
0.75V
IN
2
π
f
HF
LC 1
2
f
f
LC
–
----------------------------------------------------------------
=
C
C
0.75V
2
π
f
LC
V
PP
R
FB
f
0
f
HF
LC
1
–
2
π
-------------------------------------------------------------------
=
ISL6557A
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| ISL6557CB | 制造商:Intersil Corporation 功能描述: |
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