参数资料
型号: ISL6445IAZ
厂商: Intersil
文件页数: 14/15页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM CM 24-QSOP
标准包装: 1,000
PWM 型: 电流模式
输出数: 2
频率 - 最大: 1.55MHz
占空比: 73%
电源电压: 4.5 V ~ 24 V
降压:
升压:
回扫:
反相:
倍增器:
除法器:
Cuk:
隔离:
工作温度: -40°C ~ 85°C
封装/外壳: 24-SSOP(0.154",3.90mm 宽)
包装: 管件
ISL6445
expression is given in the capacitor selection section and the
ripple current is approximated by Equation 15:
Use a mix of input bypass capacitors to control the voltage
ripple across the MOSFETs. Use ceramic capacitors for the
Δ I L = ----------------------------------------------------------
( V IN – V OUT ) ( V OUT )
( f S ) ( L ) ( V IN )
(EQ. 15)
high frequency decoupling and bulk capacitors to supply the
RMS current. Small ceramic capacitors can be placed very
close to the upper MOSFET to suppress the voltage induced
For the ISL6445, use Inductor values between 1μH to 3.3μH.
Input Capacitor Selection
The important parameters for the bulk input capacitor(s) are
the voltage rating and the RMS current rating. For reliable
operation, select bulk input capacitors with voltage and
current ratings above the maximum input voltage and largest
RMS current required by the circuit. The capacitor voltage
rating should be at least 1.25x greater than the maximum
input voltage and 1.5x is a conservative guideline. The AC
RMS Input current varies with the load. The total RMS
current supplied by the input capacitance is as shown in
Equation 16:
in the parasitic circuit impedances.
For board designs that allow through-hole components, the
Sanyo OS-CON? series offer low ESR and good
temperature performance. For surface mount designs, solid
tantalum capacitors can be used, but caution must be
exercised with regard to the capacitor surge current rating.
These capacitors must be capable of handling the
surge-current at power-up. The TPS series available from
AVX is surge current tested.
I RMS =
where,
2 2
I RMS1 + I RMS2
(EQ. 16)
I RMSx =
DC – DC
2
(EQ. 17)
DC is duty cycle of the respective PWM.
Depending on the specifics of the input power and its
impedance, most (or all) of this current is supplied by the
input capacitor(s). Figure 18 shows the advantage of having
the PWM converters operating out of phase. If the
converters were operating in phase, the combined RMS
current would be the algebraic sum, which is a much larger
value as shown. The combined out-of-phase current is the
square root of the sum of the square of the individual
reflected currents and is significantly less than the combined
in-phase current.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
IN PHASE
OUT-OF-PHASE
1.5
1.0
0.5
3.3V
5V
0
0
1
2 3
4
5
3.3V AND 5V LOAD CURRENT
FIGURE 18. INPUT RMS CURRENT vs LOAD
14
FN9230.1
June 3, 2008
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