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參數(shù)資料
| 型號： | FAN5091 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Synchronous Multi-Slice DC-DC Controller(同步多片DC-DC轉(zhuǎn)換控制器) |
| 中文描述： | 同步多層DC - DC控制器（同步多片的DC - DC轉(zhuǎn)換控制器） |
| 文件頁數(shù)： | 17/20頁 |
| 文件大?。?/td> | 116K |
| 代理商： | FAN5091 |
FAN5091
17
A
the transition greatly affects the power dissipation. It may be
a good trade-off to select a MOSFET with a somewhat
higher R
DS,on
, if by so doing a much smaller gate charge is
available. For high current applications, it may be necessary
to use two MOSFETs in parallel for the high-side for each
slice.
For details and a spreadsheet on MOSFET selection, refer to
Applications Bulletin AB-8.
Gate Resistors
Use of a gate resistor on every MOSFET is mandatory. The
gate resistor prevents high-frequency oscillations caused by
the trace inductance ringing with the MOSFET gate capaci-
tance. In addition, the gate resistor limits the power dissipa-
tion inside the IC, which can become a limiting factor with
multiple MOSFETs operating at high frequency.
Use of a 1/10W, 2.2
resistor on a gate (or a 4.7
resistor
for each of two gates in parallel) does not significantly affect
converter efficiency or performance. The gate resistors
should be located physically as close to the MOSFET gate as
possible.
Inductor Selection
Choosing the value of the inductor is a tradeoff between
allowable ripple voltage and required transient response. A
smaller inductor produces greater ripple while producing
better transient response. In any case, the minimum induc-
tance is determined by the allowable ripple. The first order
equation (close approximation) for minimum inductance for
a two-slice converter is:
where:
Vin = Input Power Supply
Vout = Output Voltage
f = DC/DC converter switching frequency
ESR = Equivalent series resistance of all output capacitors in
parallel
Vripple = Maximum peak to peak output ripple voltage
budget.
A typical value for the inductor is 1.3
μ
H at an oscillator fre-
quency of 600KHz (300KHz each slice) and 220nH at an
oscillator frequency of 2MHz (1MHz each slice). For other
frequencies, use the interpolating formula
Schottky Diode Selection
The application circuit of Figure 1 shows a Schottky diode,
D3 (D4 respectively), one in each slice. They are used as
free-wheeling diodes to ensure that the body-diodes in Q2
and Q3 (Q5 and Q6 respectively) do not conduct when the
upper MOSFET is turning off and the lower MOSFETs are
turning on. It is undesirable for this diode to conduct because
its high forward voltage drop and long reverse recovery time
degrades efficiency, and so the Schottky provides a shunt
path for the current. Since this time duration is extremely
short, being minimized by the adaptive gate delay, the selec-
tion criterion for the diode is that the forward voltage of the
Schottky at the output current should be less than the forward
voltage of the MOSFET’s body diode. Power capability is
not a criterion for this device, as its dissipation is very small.
Output Filter Capacitors
The output bulk capacitors of a converter help determine its
output ripple voltage and its transient response. It has
already been seen in the section on selecting an inductor that
the ESR helps set the minimum inductance. For most con-
verters, the number of capacitors required is determined by
the transient response and the output ripple voltage, and
these are determined by the ESR and not the capacitance
value. That is, in order to achieve the necessary ESR to meet
the transient and ripple requirements, the capacitance value
required is already very large.
The most commonly used choice for output bulk capacitors
is aluminum electrolytics, because of their low cost and low
ESR. The only type of aluminum capacitor used should be
those that have an ESR rated at 100kHz. Consult Application
Bulletin AB-14 for detailed information on output capacitor
selection.
For higher frequency applications, particularly those running
the FAN5091 oscillator at >1MHz, ceramic capacitors may
be considered. They have much smaller ESR than compara-
ble electrolytics, but also much smaller capacitance.
Details of the selection of either type of capacitor may be
found in the appendix.
The output capacitance should also include a number of
small value ceramic capacitors placed as close as possible to
the processor; 0.1
μ
F and 0.01
μ
F are recommended values.
Input Filter
The DC-DC converter design may include an input inductor
between the system main supply and the converter input as
shown in Figure 6. This inductor serves to isolate the main
supply from the noise in the switching portion of the DC-DC
converter, and to limit the inrush current into the input capac-
itors during power up. A value of 1.3
μ
H is recommended.
L
min
V
----------------------------------
2
V
–
f
V
V
in
-----------
V
ripple
-----------------
=
L nH
)
f KHz
)
)
---------------------
240
–
≈
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相關(guān)代理商/技術(shù)參數(shù) |
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|---|---|
| FAN5091_CAB3116B WAF | 制造商:Fairchild Semiconductor Corporation 功能描述: |
| FAN5091MTC | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| FAN5091MTC_Q | 功能描述:DC/DC 開關(guān)控制器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:Texas Instruments 輸入電壓:6 V to 100 V 開關(guān)頻率: 輸出電壓:1.215 V to 80 V 輸出電流:3.5 A 輸出端數(shù)量:1 最大工作溫度:+ 125 C 安裝風格: 封裝 / 箱體:CPAK |
| FAN5091MTCX | 功能描述:直流/直流開關(guān)轉(zhuǎn)換器 Sync Buck Converter 2Phs Interleaved RoHS:否 制造商:STMicroelectronics 最大輸入電壓:4.5 V 開關(guān)頻率:1.5 MHz 輸出電壓:4.6 V 輸出電流:250 mA 輸出端數(shù)量:2 最大工作溫度:+ 85 C 安裝風格:SMD/SMT |
| FAN5091MTF | 功能描述:開關(guān)變換器、穩(wěn)壓器與控制器 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(guān)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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