参数资料
型号: ISL6307BCRZ-T
厂商: Intersil
文件页数: 29/33页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 48-QFN
标准包装: 4,000
PWM 型: 电压模式
输出数: 6
频率 - 最大: 275kHz
占空比: 66.7%
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 ~ 70°C
封装/外壳: 48-VFQFN 裸露焊盘
包装: 带卷 (TR)
ISL6307B
C 2
In the solutions to the compensation equations, there is a
single degree of freedom. For the solutions presented in
R 1 = R FB -----------------------------------------
C 1
R C
C C
COMP
FB
Equation 35, R FB is selected arbitrarily. The remaining
compensation components are then selected according to
Equation 35.
C ( ESR )
LC – C ( ESR )
C 1 = -----------------------------------------
R 1
R FB
IDROOP
LC – C ( ESR )
R FB
VDIFF
C 2 = ---------------------------------------------------------------------
V PP ? 2 π ? f 0 f HF LCR FB
R C = -----------------------------------------------------------------------
? 2 π f
- 0.75 V
HF LC – 1 ?
FIGURE 21. COMPENSATION CIRCUIT FOR ISL6307B BASED
CONVERTER WITHOUT LOAD-LINE
REGULATION
In Equation 34, L is the per-channel filter inductance divided
0.75V IN
( 2 π ) 2 f 0 f HF LCR FB V P-P
2
? ?
?
IN ?
0.75V IN ? 2 π f
HF LC – 1 ?
C C = ---------------------------------------------------------------------
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 P-P is the peak-to-
peak sawtooth signal amplitude as described in Figure 7 and
?
?
( 2 π ) 2 f 0 f HF LCR FB V P-P
(EQ. 35)
Electrical Specifications .
The optional capacitor C 2 , is sometimes needed to bypass
noise away from the PWM comparator (see Figure 20). Keep
a position available for C 2 , and be prepared to install a high-
frequency capacitor of between 22pF and 150pF in case any
leading-edge jitter problem is noted.
Once selected, the compensation values in Equation 34
assure a stable converter with reasonable transient
performance. 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
Equation 34 unless some performance issue 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 21, 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 rule is to choose f HF = 10f 0 , but it can be
higher if desired. Choosing f HF to be lower than 10f 0 can
cause problems with too much phase shift below the system
bandwidth.
29
In Equation 35, 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 P-P is the peak-to-
peak sawtooth signal amplitude as described in Figure 7 and
Electrical Specifications .
Output Filter Design
The output inductors and the output capacitor bank together
to form a low-pass filter responsible for smoothing the
pulsating voltage at the phase nodes. The output filter also
must provide the transient energy until the regulator can
respond. Because it has a low bandwidth compared to the
switching frequency, the output filter necessarily limits the
system transient response. The output capacitor must
supply or sink load current while the current in the output
inductors increases or decreases to meet the demand.
In high-speed converters, the output capacitor bank is
usually the most costly (and often the largest) part of the
circuit. Output filter design begins with minimizing the cost of
this part of the circuit. The critical load parameters in
choosing the output capacitors are the maximum size of the
load step, ? I; the load-current slew rate, di/dt; and the
maximum allowable output-voltage deviation under transient
loading, ? V MAX . Capacitors are characterized according to
their capacitance, ESR, and ESL (equivalent series
inductance).
At the beginning of the load transient, the output capacitors
supply all of the transient current. The output voltage will
initially deviate by an amount approximated by the voltage
drop across the ESL. As the load current increases, the
FN9225.0
March 9, 2006
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