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參數資料
| 型號： | FAN5240 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Multi-Phase PWM Controller for AMD Mobile Athlon TM and Duron TM |
| 中文描述： | 多相PWM控制器的AMD移動Athlon和Duron商標商標 |
| 文件頁數： | 14/19頁 |
| 文件大小： | 447K |
| 代理商： | FAN5240 |
FAN5240
PRODUCT SPECIFICATION
14
REV. 1.1.7 8/29/02
Design and Component Selection
Guidelines
As an initial step, define operating voltage range and mini-
mum and maximum load currents for the controller. For this
discussion,
Output Inductor Selection
The minimum practical output inductor value is the one that
keeps inductor current just on the boundary of continuous
conduction at some minimum load. The industry standard
practice is to choose the ripple current to be somewhere from
15% to 35% of the nominal current. At light load, the ripple
current also determines the point where the converter will
automatically switch to hysteretic mode of operation (I
MIN
)
to sustain high efficiency. The following equations help to
choose the proper value of the output filter inductor.
where
I is the inductor ripple current, which we will choose
for 20% of the full load current (12.5A in each phase) and
V
OUT
is the maximum output ripple voltage allowed.
for this example we’ll use:
V
IN
= 20V, V
OUT
= 1.5V
I = 20% *12.5A (per phase) = 2.5A
F
SW
= 300KHz.
Therefore,
L
≈
1.8
μ
H
The inductor's current rating should be chosen per the
I
LIMIT
calculated above. Some transient currents over the
inductor current rating may be tolerable if the inductor’s
saturation characteristic
is sufficiently “soft”.
Output Capacitor Selection
The output capacitor serves two major functions in a switch-
ing power supply. Along with the inductor it filters the
sequence of pulses produced by the switcher, and it supplies
the load transient currents. The filtering requirements are a
function of the switching frequency and the ripple current
allowed, and are usually easy to satisfy in high frequency
converters.
The load transient requirements are a function of the slew
rate (di/dt) and the magnitude of the transient load current.
Modern microprocessors produce transient load rates in
excess of 10A/
μ
s. High frequency ceramic capacitors placed
beneath the processor socket initially supply the transient
and reduce the slew rate seen by the bulk capacitors. The
bulk capacitor values are generally determined by the total
allowable ESR rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the processor power pins as physically possible.
Consult with the processor manufacturer for specific
decoupling requirements. Use only specialized low-ESR
electrolytic capacitors intended for switching-regulator
applications for the bulk capacitors. The bulk capacitor’s
ESR will determine the output ripple voltage and the initial
voltage drop after a transient. In most cases, multiple electro-
lytic capacitors of small case size perform better than a
single large case capacitor.
Input Capacitor Selection
The input capacitor should be selected by its ripple current
rating. For a 2 phase converter, the RMS currents is calcu-
lated:
This equation produces the worst case value at maximum
duty cycle. For our example, that occurs when VIN = 5.5V
and VOUT = 2V. For 25A maximum output the maximum
RMS current at C
IN
:
Power MOSFET Selection
For the example in the following discussion, we will be
selecting components for:
VIN from 5V to 20V
V
OUT
= 1.5V @ I
LOAD(MAX)
= 12.5A/phase
The FAN5240 converter’s output voltage is very low with
respect to the input voltage, therefore the Lower MOSFET
(Q2) is conducting the full load current for most of the cycle.
Therefore, Q2 should be selected to be a MOSFET with low
R
DS(ON)
to minimize conduction losses.
In contrast, Q1 is on for a maximum of 20% (when VIN =
5V) of the cycle, and its conduction loss will have less of an
impact. Q1, however, sees most of the switching losses, so
Q1’s primary selection criteria should be gate charge
(Q
G(SW)
).
IOUT Max
VIN
VOUT
25A
5.5 to 21 V
0.925 to 2 V
I
2
I
MIN
×
V
------------------
=
=
,
L
V
SW
V
I
–
-----------------------------
V
IN
--------------
×
=
(13)
------
I
RMS
I
-------
2D
4D
2
–
=
(14)
I
RMS MAX
)
5.6A
=
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相關代理商/技術參數 |
參數描述 |
|---|---|
| FAN5240_06 | 制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Multi-Phase PWM Controller for AMD Mobile Athlon and Duron |
| FAN5240_ADC3116B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5240MTC | 功能描述:開關變換器、穩壓器與控制器 DC/DC RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5240MTC_Q | 功能描述:開關變換器、穩壓器與控制器 DC/DC RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
| FAN5240MTCX | 功能描述:開關變換器、穩壓器與控制器 PWM Controller Two Phase RoHS:否 制造商:Texas Instruments 輸出電壓:1.2 V to 10 V 輸出電流:300 mA 輸出功率: 輸入電壓:3 V to 17 V 開關頻率:1 MHz 工作溫度范圍: 安裝風格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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