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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)： | 16/20頁 |
| 文件大?。?/td> | 116K |
| 代理商： | FAN5091 |
FAN5091
16
A
Power Good (PWRGD)
The FAN5091 Power Good function is designed in accor-
dance with the Pentium III DC-DC converter specifications
and provides a continuous voltage monitor on the VFB pin.
The circuit compares the VFB signal to the VREF voltage
and outputs an active-low interrupt signal to the CPU should
the power supply voltage deviate more than ±12% of its
nominal setpoint. The output is guaranteed open-collector
high when the power supply voltage is within ±7% of its
nominal setpoint. The Power Good flag provides no control
functions to the FAN5091.
Output Enable/Soft Start (ENABLE/SS)
The FAN5091 will accept an open collector/TTL signal for
controlling the output voltage. The low state disables the out-
put voltage. When disabled, the PWRGD output is in the low
state.
Even if an enable is not required in the circuit, this pin
should have attached a capacitor (typically 100nF) to soft-
start the switching. A softstart capacitor may be approxi-
mately chosen by the formula:
Oscillator
The FAN5091 oscillator section runs at a frequency deter-
mined by a resistor from the RT pin to ground according to
the formula
The oscillator generates two internal sawtooth ramps, each at
one-half the oscillator frequency, and running 180
°
out of
phase with each other. These ramps cause the turn-on time of
the two slices to be phased apart. The oscillator frequency of
the FAN5091 can be programmed from 200KHz to 2MHz.
Selection of a frequency will depend on various system per-
formance criteria, with higher frequency resulting in smaller
components but lower efficiency.
Programmable Active Droop
The FAN5091 features Programmable Active Droop: as
the output current increases, the output voltage drops propor-
tionately an amount that can be programmed with an exter-
nal resistor. This feature is offered in order to allow
maximum headroom for transient response of the converter.
The current is sensed losslessly by measuring the voltage
across the low-side MOSFET during its on time. Consult the
section on current sensing for details. Note that this method
makes the droop dependent on the temperature and initial
tolerance of the MOSFET, and the droop must be calculated
taking account of these tolerances. Given a maximum output
current, the amount of droop can be programmed with a
resistor to ground on the droop pin, according to the formula
Typical response time of the FAN5091 to an output voltage
change is 100nsec.
Important Note!
The oscillator frequency must be selected
before selecting the droop resistor, because the value of RT
is used in the calculation of R
Droop
.
Higher Current Converters
Active droop makes it possible to parallel multiple
FAN5091s for even higher output current requirements.
Please refer to Application Bulletin AB-XX for details.
Over-Voltage Protection
The FAN5091 constantly monitors the output voltage for
protection against over-voltage conditions. If the voltage at
the VFB pin exceeds 2.2V, an over-voltage condition is
assumed and the FAN5091 latches on the external low-side
MOSFET and latches off the high-side MOSFET. The DC-
DC converter returns to normal operation only after V
CC
has
been recycled.
Over Temperature Protection
If the RC5091 die temperature exceeds approximately
150
°
C, the IC shuts itself off. It remains off until the temper-
ature has dropped approximately 25
°
C, at which time it
resumes normal operation.
Component Selection
MOSFET Selection
This application requires N-channel Enhancement Mode Field
Effect Transistors. Desired characteristics are as follows:
Low Drain-Source On-Resistance,
R
DS,ON
< 10m
(lower is better);
Power package with low Thermal Resistance;
Drain-Source voltage rating > 15V;
Low gate charge, especially for higher frequency
operation.
For the low-side MOSFET, the on-resistance (R
DS,ON
) is the
primary parameter for selection. Because of the small duty
cycle of the high-side, the on-resistance determines the
power dissipation within the low-side MOSFET and therefore
significantly affects the efficiency of the DC-DC converter.
For high current applications, it may be necessary to use two
MOSFETs in parallel for the low-side for each slice.
For the high-side MOSFET, the gate charge is as important
as the on-resistance, especially with a 12V input and with
higher switching frequencies. This is because the speed of
C
A
out
----+
=
R
T
(
)
---------------------
9
f Hz
)
=
R
Droop
V
I
max
R
DS on
2
---------------------------------------------
=
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| 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(fēng)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(fēng)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(fēng)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(fēng)格:SMD/SMT 封裝 / 箱體:WSON-8 封裝:Reel |
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