参数资料
型号: ISL6307CRZ
厂商: Intersil
文件页数: 31/34页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 48-QFN
标准包装: 43
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: 管件
ISL6307
At the beginning of the load transient, the output capacitors
supply all of the transient current. The output voltage will
inductance, C is the total output capacitance, and N is the
number of active channels.
L ≤ --------------------- ? V MAX – ? I ( ESR )
L ≤ -------------------------- ? V MAX – ? I ( ESR ) ? V IN – V O ?
( ? I ) 2
initially deviate by an amount approximated by the voltage
drop across the ESL. As the load current increases, the
voltage drop across the ESR increases linearly until the load
current reaches its final value. The capacitors selected must
have sufficiently low ESL and ESR so that the total output-
voltage deviation is less than the allowable maximum.
Neglecting the contribution of inductor current and regulator
response, the output voltage initially deviates by an amount
2NCV O
( ? I ) 2
( 1.25 ) NC
Switching Frequency
? ?
(EQ. 38)
(EQ. 39)
? V ≈ ( ESL ) ----- + ( ESR ) ? I
di
dt
(EQ. 36)
There are a number of variables to consider when choosing
the switching frequency, as there are considerable effects on
the upper-MOSFET loss calculation. These effects are
The filter capacitor must have sufficiently low ESL and ESR
so that ? V < ? V MAX .
Most capacitor solutions rely on a mixture of high-frequency
capacitors with relatively low capacitance in combination
with bulk capacitors having high capacitance but limited
high-frequency performance. Minimizing the ESL of the
high-frequency capacitors allows them to support the output
voltage as the current increases. Minimizing the ESR of the
bulk capacitors allows them to supply the increased current
with less output voltage deviation.
outlined in MOSFETs , and they establish the upper limit for
the switching frequency. The lower limit is established by the
requirement for fast transient response and small output-
voltage ripple as outlined in Output Filter Design . Choose the
lowest switching frequency that allows the regulator to meet
the transient-response requirements.
Switching frequency is determined by the selection of the
frequency-setting resistor, R T (see the figures labelled
Typical Application on pages 4, 5, 6 and 7). Equation 40 is
provided to assist in selecting the correct value for R T .
2.5X 10
R T = -------------------------- – 600
The ESR of the bulk capacitors also creates the majority of
the output-voltage ripple. As the bulk capacitors sink and
source the inductor ac ripple current (see Interleaving and
F SW
10
(EQ. 40)
Equation 2), a voltage develops across the bulk-capacitor
ESR equal to I C,PP (ESR). Thus, once the output capacitors
are selected, the maximum allowable ripple voltage,
V PP(MAX) , determines the lower limit on the inductance.
Input Capacitor Selection
The input capacitors are responsible for sourcing the AC
component of the input current flowing into the upper
MOSFETs. Their RMS current capacity must be sufficient to
– N V OUT ? V OUT
? V
L ≥ ( ESR ) ------------------------------------------------------------
? IN ?
f S V IN V PP ( MAX )
(EQ. 37)
handle the AC component of the current drawn by the upper
MOSFETs that is related to duty cycle and the number of
active phases.
Since the capacitors are supplying a decreasing portion of
the load current while the regulator recovers from the
transient, the capacitor voltage becomes slightly depleted.
The output inductors must be capable of assuming the entire
load current before the output voltage decreases more than
? V MAX . This places an upper limit on inductance.
Equation 38 gives the upper limit on L for the cases when
the trailing edge of the current transient causes a greater
0.3
0.2
output-voltage deviation than the leading edge. Equation 39
addresses the leading edge. Normally, the trailing edge
dictates the selection of L because duty cycles are usually
less than 50%. Nevertheless, both inequalities should be
evaluated, and L should be selected based on the lower of
0.1
I L,PP = 0
I L,PP = 0.5 I O
I L,PP = 0.75 I O
the two results. In each equation, L is the per-channel
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE (V O /V IN )
FIGURE 22. NORMALIZED INPUT-CAPACITOR RMS CURRENT
vs DUTY CYCLE FOR 2-PHASE CONVERTER
31
FN9224.0
March 9, 2006
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