- 您現在的位置：買賣IC網 > PDF目錄377971 > ML4880 (Fairchild Semiconductor Corporation) Portable PC/PCMCIA Power Controller(便攜式PC/PCMCIA電源控制器) PDF資料下載
參數資料
| 型號： | ML4880 |
| 廠商： | Fairchild Semiconductor Corporation |
| 英文描述： | Portable PC/PCMCIA Power Controller(便攜式PC/PCMCIA電源控制器) |
| 中文描述： | 便攜式電腦/ PCMCIA的電源控制器（便攜式電腦/電源控制器的PCMCIA） |
| 文件頁數： | 10/15頁 |
| 文件大小： | 164K |
| 代理商： | ML4880 |
ML4880
10
The relationship of the inductor current to the output
current is given by the following equation:
I
I
I
V
+
V
V
V
R
T
V
L
V
+
V
V
OUT
SENSE
L
IN
IN
OUT
SENSE
SENSE
ON
IN
IN
IN
OUT
=
+
+
×
×
1
2
2
(18)
The inductance value can be determined by setting the
ripple current portion of Equation 18 to some percentage
of the output current. Inductor ripple currents in the range
of 50% to 80% of the maximum output current are
typical. As a good starting point set the inductor ripple
current to 65% of the maximum output current:
I
T
V
L
F
I
V
V
V
L
ON
IN
IRC
OUT MAX
(
IN
OUT
IN
=
×
=
×
×
+
)
(19)
where F
IRC
= ratio of inductor ripple current to the
maximum output current, or:
L
T
V
I
V
V
V
ON
IN MIN
(
OUT MAX
(
IN MIN
(
IN MIN
(
OUT
=
×
×
+
)
)
)
)
.65
(20)
Calculate the inductance using the volt-seconds value
given in Figure 5 at the minimum input voltage. Choose
the nearest standard value, and determine the actual
inductor ripple current at the maximum and minimum
input voltage using Equation 19 and Figure 5.
Next, determine the sense resistor value using the inductor
ripple current value calculated above using:
R
V
I
V
V
V
I
I
V
V
V
I
SENSE
SENSE MIN
+
)
OUT MAX
(
IN MIN
(
OUT
IN MIN
(
L MIN
(
OUT MAX
(
IN MIN
(
OUT
IN MIN
(
L MIN
(
=
=
+
(
)
)
)
)
)
)
)
)
.
1
2
0 14
1
2
(21)
Having determined the values for the inductor and sense
resistor, the inductor peak current rating can now be
specified. This value is calculated at current limit and at
the maximum input voltage, and is given by:
I
I
I
V
R
I
V
R
I
L PK
(
MAX
SENSE MAX
L MAX
(
SENSE MAX
SENSE
L MAX
(
SENSE
L MAX
(
@
)
(
)
)
(
)
)
)
.
=
+
=
+
=
+
0 25
(22)
For reliable operation, the inductor current rating should
exceed the value calculated by 10%-20%.
Now the sense resistor’s power rating can be determined.
The sense resistor must be able to carry the peak current
in the inductor, but only during the OFF-time:
P
I
R
R
RMS OFF
(
SENSE
SENSE
=
×
)
2
(23)
where,
I
V
V
V
I
I
I
I
RMS OFF
(
IN MAX
(
IN MAX
(
OUT
SENSE MAX
SENSE MAX
L PK
(
MAX
L PK
(
MAX
)
)
)
(
)
(
)
@
)
@
)
(
)
(
)(
)
(
)
2
2
2
3
=
+
+
+
The winding resistance and the turns ratio of the coupled
inductor need to be specified. In general the winding
resistance should be as low as possible, preferably in the
low milliohm range. A good rule of thumb is to allow 2
mW of winding resistance per mH of inductance. The
turns ratio is specified at 1:1 for simplicity and availability.
FLYBACK REGULATOR - MOSFET SELECTION
The internal gate drive of the ML4880 limits the selection
of the switching FET to logic level types with the ON
resistance specified at V
GS
= 4.5V. Also, look for a FET
with a maximum total gate charge of around 70nC.
The drain to source breakdown voltage rating is
determined as follows:
V
V
(
V
F
DS
IN MAX
(
OUT
DS
=
+
×
)
)
(24)
A safety derating factor, F
DS
, in the range of 1.5 to 2.0 is
recommended due to the voltage spikes caused by the
leakage inductance of a transformer. For a more reliable
design, look for MOSFETs that are avalanche rated.
The maximum ON resistance of the MOSFET can be
determined using the worst case power dissipation for the
package type chosen. This assumes that the major portion
of heat generated in the package is due to I
2
R losses.
R
P
I
DS ON
(
PKG
RMS ON
)
(
)
=
2
(25)
where,
I
V
V
V
I
I
I
I
RMS ON
OUT
+
IN MIN
(
OUT
SENSE MAX
SENSE MAX
L PK
(
MAX
L PK
(
MAX
(
)
)
(
)
(
)
@
)
@
)
(
)
(
)(
)
(
)
2
2
2
3
=
+
+
FLYBACK REGULATOR — RECTIFIER SELECTION
The output diode must be able to carry the worst case
output current as well as withstand the worst case reverse
voltage. The worst case output current occurs at current
limit and at the maximum input voltage. Therefore, the
average forward current rating of the output diode can be
determined by the following:
I
I
F
R
T
V
×
L
V
V
V
F
D AVG
(
OUT MAX
(
ID
SENSE
ON
IN MAX
(
IN MAX
(
IN MAX
(
OUT
ID
)
)
)
)
)
.
=
=
+
×
2
+
0 25
1
where,
F
derating factor
ID
=
(26)
The derating factor is typically in the range of 0.5 to 0.9
depending on reliability goals. Typically a value of 0.8 is
used for most applications.
The reverse voltage rating is determined by the sum of the
output voltage and the maximum input voltage:
相關PDF資料 |
PDF描述 |
|---|---|
| ML4890 | High Efficiency, Low Ripple Boost Regulator(輸出可調、小波紋升壓穩(wěn)壓器) |
| ML4894 | Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的同步補償控制器（5.9V～15V到5V變換）) |
| ML4895 | Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的同步補償控制器（5.9V～15V到2.5V～4V變換）) |
| ML4900 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補償控制器（5V到2.1V～3.5V變換）) |
| ML4901 | High Current Synchronous Buck Controller For DC/DC conversion(用于DC/DC變換的大電流同步補償控制器（12V到2.1V～3.5V變換）) |
相關代理商/技術參數 |
參數描述 |
|---|---|
| ML4880CS | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Portable PC/PCMCIA Power Controller |
| ML4880ES | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:Portable PC/PCMCIA Power Controller |
| ML4890 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
| ML4890CS-3 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
| ML4890CS-5 | 制造商:MICRO-LINEAR 制造商全稱:MICRO-LINEAR 功能描述:High Efficiency, Low Ripple Boost Regulator |
發(fā)布緊急采購，3分鐘左右您將得到回復。