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參數(shù)資料
| 型號： | FAN5240MSA |
| 廠商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | DUAL SWITCHING CONTROLLER, 345 kHz SWITCHING FREQ-MAX, PDSO28 |
| 封裝： | QSOP-28 |
| 文件頁數(shù)： | 3/15頁 |
| 文件大小： | 250K |
| 代理商： | FAN5240MSA |
PRODUCT SPECIFICATION
FAN5240
REV. 1.0.2 10/10/01
11
Overvoltage Protection
When the output voltage of the converter exceeds approxi-
mately 120% of nominal, it enters into over-voltage protec-
tion, with the goal of protecting the load from damage.
In over-voltage protection, the high-side MOSFET is turned
off and the low-side MOSFET is turned on, crowbarring the
output. Once over-voltage protection is triggered, it remains
on until the output returns to its normal value.
Power Good
Power good is asserted when the supply is within its
specied tolerance. Power good is delayed a minimum of
10msec after the output voltage comes into regulation. The
delay can be set by selection of the DELAY pin capacitor,
according to the equation
Shutdown
The ENABLE pin does the on/off control. Pulling the
ENABLE pin low turns off the converter.
Thermal shutdown
If the die temperature of the FAN5240 exceeds safe limits,
the IC shuts itself off. The thermal shutdown has built-in
hysteresis.
MOSFET Selection
The notebook application circuit shown in Figure 1 is
designed to run with an input voltage operating range of
6-24V. This high input voltage range (relative to the output
voltage) helps determine the selection of the MOSFETs,
since the high-side MOSFET is on (Vout / Vin) of the time,
and the low-side MOSFET 1 – (Vout / Vin) of the time.
The duty cycle maxima and minima for minimum and
maximum output voltages are tabulated in Table 3.
Table 3. MOSFET Duty Cycles
High-side FET
Low-side FET
In every case, the high-side MOSFET is on a very short time,
and the low-side MOSFET is on a long time. Thus the high-
side MOSFET should be selected for low switching loss,
whereas the low-side MOSFET must be selected for low
RDS,on.
Schottky Selection
A schottky diode is not required in Figure 1, because the
low-side MOSFETs have built in schottkies using Fairchild
SyncFET technology. If some other type of MOSFET is
used, a schottky must be used in anti-parallel with the
low-side MOSFET. Selection of a schottky is determined by
the maximum output. In the converter of Figure 1, maximum
output current is 24A or 12A per slice, and suppose the
MOSFET has a body diode Vf = 0.75V at this current. The
schottky must have at least 100mV less Vf at the same cur-
rent to ensure that the body diode does not turn on. The
MBRD835L diode has Vf = 0.6V guaranteed maximum at
12A at 25°C, and so is a suitable choice.
Inductor Selection
The inductor for each slice of the converter should be chosen
with a value sufciently large to guarantee that the converter
remains in continuous conduction mode at the load current at
which it switches to PFM mode:
where Vin is the maximum input voltage, IPFM is the
current at which it switches to PFM mode, and f is the
minimum switching frequency. Taking the case shown in
Figure 1, where the mode transition occurs at 2A, the
inductance should be larger than:
Output Cap Selection for the CPU
The output capacitor for the converter is selected to meet the
transient requirements of the load. The CPU can transition
from no load to maximum load almost instantaneously, and
is required to maintain ±100mV regulation during the transi-
tion. To meet this, the ESR of the output capacitors must be
Input Capacitor Selection
Input capacitor selection is determined by RMS ripple
current rating. The two slices are phased 180° apart. Ripple
current is determined by the formula
Vout
Vin
6V
24V
0.925V
.15
.04
2.000V
.33
.08
Vout
Vin
6V
24V
0.925V
.75
.96
2.000V
.67
.92
t10m
C
20nF
-------------
sec
=
.
L
V
out
V
out
2
V
in
-------------
–
2I
PFM
×
f
×
-------------------------------
≥
L
1.4V
()
2
24V
-------------------
–
22A
×
255KHz
×
--------------------------------------------
≥
H
=
ESR
100mV
24A
------------------
≤
4.1m
=
I
rms
I
2
--- 2DC-4DC
2
×
=
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| FAN5240MTC | 功能描述:開關(guān)變換器、穩(wěn)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(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 |
| FAN5240MTC_Q | 功能描述:開關(guān)變換器、穩(wěn)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(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 |
| FAN5240MTCX | 功能描述:開關(guān)變換器、穩(wěn)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(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 |
| FAN5240QSC | 功能描述:開關(guān)變換器、穩(wěn)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(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 |
| FAN5240QSCX | 功能描述:開關(guān)變換器、穩(wěn)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(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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