参数资料
型号: ISL6326CRZ
厂商: Intersil
文件页数: 29/30页
文件大小: 0K
描述: IC REG CTRLR BUCK PWM VM 40-QFN
标准包装: 50
PWM 型: 电压模式
输出数: 1
频率 - 最大: 275kHz
占空比: 25%
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: 40-VFQFN 裸露焊盘
包装: 管件
ISL6326
0.3
I L(P-P) = 0
I L(P-P) = 0.5 I O
0.6
0.2
0.1
I L(P-P) = 0.25 I O
I L(P-P) = 0.75 I O
0.4
0.2
I L(P-P) = 0
I L(P-P) = 0.5 I O
I L(P-P) = 0.75 I O
0
0
0.2
0.4
0.6
0.8
1.0
0
0
0.2
0.4
0.6
0.8
1.0
DUTY CYCLE (V O/ V IN )
FIGURE 20. NORMALIZED INPUT-CAPACITOR RMS CURRENT
vs DUTY CYCLE FOR 4-PHASE CONVERTER
Figures 19 and 20 provide the same input RMS current
information for three and four phase designs respectively.
Use the same approach to selecting the bulk capacitor type
and number as described previously.
Low capacitance, high-frequency ceramic capacitors are
needed in addition to the bulk capacitors to suppress leading
and falling edge voltage spikes. The result from the high
current slew rates produced by the upper MOSFETs turn on
and off. Select low ESL ceramic capacitors and place one as
close as possible to each upper MOSFET drain to minimize
board parasitic impedances and maximize suppression.
MULTIPHASE RMS IMPROVEMENT
Figure 21 is provided as a reference to demonstrate the
dramatic reductions in input-capacitor RMS current upon the
implementation of the multiphase topology. For example,
compare the input RMS current requirements of a two-phase
converter vs that of a single phase. Assume both converters
have a duty cycle of 0.25, maximum sustained output current
of 40A, and a ratio of I L(P-P) to I O of 0.5. The single phase
converter would require 17.3A RMS current capacity while the
two-phase converter would only require 10.9A RMS . The
advantages become even more pronounced when output
current is increased and additional phases are added to
keep the component cost down relative to the single phase
approach.
DUTY CYCLE (V O/ V IN )
FIGURE 21. NORMALIZED INPUT-CAPACITOR RMS
CURRENT vs DUTY CYCLE FOR SINGLE-PHASE
CONVERTER
Layout Considerations
The following layout strategies are intended to minimize the
impact of board parasitic impedances on converter
performance and to optimize the heat-dissipating capabilities
of the printed-circuit board. These sections highlight some
important practices which should not be overlooked during the
layout process.
Component Placement
Within the allotted implementation area, orient the switching
components first. The switching components are the most
critical because they carry large amounts of energy and tend
to generate high levels of noise. Switching component
placement should take into account power dissipation. Align
the output inductors and MOSFETs such that space between
the components is minimized while creating the PHASE
plane. Place the Intersil MOSFET driver IC as close as
possible to the MOSFETs they control to reduce the parasitic
impedances due to trace length between critical driver input
and output signals. If possible, duplicate the same placement
of these components for each phase.
Next, place the input and output capacitors. Position one high-
frequency ceramic input capacitor next to each upper
MOSFET drain. Place the bulk input capacitors as close to the
upper MOSFET drains as dictated by the component size and
dimensions. Long distances between input capacitors and
MOSFET drains result in too much trace inductance and a
reduction in capacitor performance. Locate the output
capacitors between the inductors and the load, while keeping
them in close proximity to the microprocessor socket.
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
29
FN9262.1
May 5, 2008
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