参数资料
| 型号： | NCP5322ADWR2 |
| 厂商： | ON Semiconductor |
| 文件页数： | 18/31页 |
| 文件大小： | 0K |
| 描述： | IC CTRLR BUCK 2PH STEPDWN 28SOIC |
| 产品变化通告： | Product Obsolescence 11/Feb/2009 |
| 标准包装： | 1 |
| 应用： | 控制器，高性能处理器 |
| 输入电压： | 4.5 V ~ 14 V |
| 输出数： | 2 |
| 输出电压： | 3.3V |
| 工作温度： | 0°C ~ 70°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 28-SOIC（0.295"，7.50mm 宽） |
| 供应商设备封装： | 28-SOIC |
| 包装： | 剪切带 (CT) |
| 其它名称： | NCP5322ADWR2OSCT |
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NCP5322A
(VIN * VOUT) @ VOUT
( a @ IO,MAX @ VIN @ fSW)
and R CS2 ) are made at identical locations to
equalize the PCB resistance added to the current
sense paths. This will help to insure acceptable
current sharing.
16. Place the 0.1 m F ceramic capacitors, C Q1 and C Q2 ,
close to the drains of the MOSFETs Q1 and Q2,
respectively.
Design Procedure
1. Output Capacitor Selection
The output capacitors filter the current from the output
inductor and provide a low impedance for transient load
current changes. Typically, microprocessor applications
will require both bulk (electrolytic, tantalum) and low
impedance, high frequency (ceramic) types of capacitors.
The bulk capacitors provide “hold up” during transient
loading. The low impedance capacitors reduce steady?state
ripple and bypass the bulk capacitance when the output
current changes very quickly. The microprocessor
manufacturers usually specify a minimum number of
ceramic capacitors. The designer must determine the
number of bulk capacitors.
Choose the number of bulk output capacitors to meet the
peak transient requirements. The formula below can be used
to provide a starting point for the minimum number of bulk
capacitors (N OUT,MIN ):
value will result in very large ripple currents in the power
components (MOSFETs, capacitors, etc) resulting in
increased dissipation and lower converter efficiency. Also,
increased ripple currents will force the designer to use
higher rated MOSFETs, oversize the thermal solution, and
use more, higher rated input and output capacitors ? the
converter cost will be adversely effected.
One method of calculating an output inductor value is to
size the inductor to produce a specified maximum ripple
current in the inductor. Lower ripple currents will result in
less core and MOSFET losses and higher converter
efficiency. Equation 3 may be used to calculate the minimum
inductor value to produce a given maximum ripple current
( α ) per phase. The inductor value calculated by this equation
is a minimum because values less than this will produce more
ripple current than desired. Conversely, higher inductor
values will result in less than the maximum ripple current.
(3)
LoMIN +
α is the ripple current as a percentage of the maximum
output current per phase ( α = 0.15 for ± 15%, α = 0.25 for
± 25%, etc). If the minimum inductor value is used, the
inductor current will swing ± α % about its value at the center
(1/2 the DC output current for a two?phase converter).
Therefore, for a two?phase converter, the inductor must be
designed or selected such that it will not saturate with a peak
NOUT,MIN + ESR per capacitor @
D IO,MAX
D VO,MAX
(1)
current of (1 + α ) ? I O,MAX /2.
The maximum inductor value is limited by the transient
In reality, both the ESR and ESL of the bulk capacitors
determine the voltage change during a load transient
according to:
D VO,MAX + ( D IO,MAX D t) @ ESL ) D IO,MAX @ ESR (2)
Unfortunately, capacitor manufacturers do not specify the
ESL of their components and the inductance added by the
PCB traces is highly dependent on the layout and routing.
Therefore, it is necessary to start a design with slightly more
response of the converter. If the converter is to have a fast
transient response then the inductor should be made as small
as possible. If the inductor is too large its current will change
too slowly, the output voltage will droop excessively, more
bulk capacitors will be required, and the converter cost will
be increased. For a given inductor value, its interesting to
determine the times required to increase or decrease the
current.
For increasing current:
than the minimum number of bulk capacitors and perform
D tINC + Lo @ D IO (VIN * VOUT)
(3.1)
D tDEC + Lo @ D IO (VOUT)
transient testing or careful modeling/simulation to
determine the final number of bulk capacitors.
2. Output Inductor Selection
The output inductor may be the most critical component
in the converter because it will directly effect the choice of
other components and dictate both the steady?state and
transient performance of the converter. When selecting an
inductor the designer must consider factors such as DC
current, peak current, output voltage ripple, core material,
magnetic saturation, temperature, physical size, and cost
(usually the primary concern).
In general, the output inductance value should be as low
and physically small as possible to provide the best transient
For decreasing current:
(3.2)
For typical processor applications with output voltages
less than half the input voltage, the current will be increased
much more quickly than it can be decreased. It may be more
difficult for the converter to stay within the regulation limits
when the load is removed than when it is applied ? excessive
overshoot may result.
The output voltage ripple can be calculated using the
output inductor value derived in this Section (Lo MIN ), the
number of output capacitors (N OUT,MIN ) and the per
capacitor ESR determined in the previous Section:
response and minimum cost. If a large inductance value is
used, the converter will not respond quickly to rapid changes
in the load current. On the other hand, too low an inductance
VOUT,P?P + (ESR per cap NOUT,MIN) @
(VIN * #Phases @ VOUT) @ D (LoMIN @ fSW)
(4)
http://onsemi.com
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