参数资料
型号: ISL6569ACR-T
厂商: Intersil
文件页数: 18/22页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM 32-QFN
标准包装: 6,000
PWM 型: 电流/电压模式
输出数: 1
频率 - 最大: 2MHz
占空比: 75%
电源电压: 4.75 V ~ 5.25 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: 0°C ~ 85°C
封装/外壳: 32-VFQFN 裸露焊盘
包装: 带卷 (TR)
ISL6569A
------------------- > f 0
R C = R FB ------------------------------------
0.75V
2 π V PP R FB f 0
COMPENSATING LOAD-LINE REGULATED
CONVERTER
The load-line regulated converter behaves in a similar
manner to a peak-current mode controller because the two
poles at the output-filter L-C resonant frequency split with
the introduction of current information into the control loop.
The final location of these poles is determined by the system
.
Case 1:
1
2 π LC
2 π f 0 V pp LC
IN
0.75V IN
C C = ------------------------------------
function, the gain of the current signal, and the value of the
------------------- ≤ f 0 < ------------------------------
compensation components, R C and C C .
Since the system poles and zero are effected by the values
Case 2:
1 1
2 π LC 2 π C ( ESR )
R C = R FB --------------------------------------------
0.75 V
C C = -------------------------------------------------------------
PP R FB LC
( 2 π ) 2 f 2 V
of the components that are meant to compensate them, the
solution to the system equation becomes fairly complicated.
Fortunately there is a simple approximation that comes very
close to an optimal solution. Treating the system as though it
were a voltage-mode regulator by compensating the L-C
poles and the ESR zero of the voltage-mode approximation
V PP ( 2 π ) 2 f 02 LC
IN
0.75V IN
0
(EQ. 27)
f 0 > ------------------------------
yields a solution that is always stable with very close to ideal
transient performance.
Case 3:
1
2 π C ( ESR )
0.75 V IN ( ESR )
2 π V PP R FB f 0 L
The feedback resistor, R FB , has already been chosen as
outlined in Load-Line Regulation Resistor . Select a target
bandwidth for the compensated system, f 0 . The target
bandwidth must be large enough to assure adequate
transient performance, but smaller than 1/3 of the per-
channel switching frequency. 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 which follow, there is a separate set
of equations for the compensation components.
C 2 (OPTIONAL)
2 π f 0 V pp L
R C = R FB ------------------------------------------
0.75V IN ( ESR ) C
C C = -------------------------------------------------
Once selected, the compensation values in Equations 27
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 27 unless some performance issue is noted.
R C
C C
COMP
The optional capacitor C 2 , is sometimes needed to bypass
noise away from the PWM comparator (see Figure 13). Keep
FB
a position available for C 2 , and be prepared to install a high-
frequency capacitor of between 22pF and 150pF in case any
R FB
+
V DROOP
-
IOUT
VDIFF
trailing edge 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 14, provides the necessary
FIGURE 13. COMPENSATION CONFIGURATION FOR
LOAD-LINE REGULATED ISL6569A CIRCUIT
In Equations 27, L is the per-channel filter inductance
divided by 2 (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 6 and Electrical Specifications .
18
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 rule is to chose f HF = 10 f 0 , but it can be higher
if desired. Choosing f HF to be lower than 10 f 0 can cause
problems with too much phase shift below the system
bandwidth.
FN9092.2
December 29, 2004
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