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參數(shù)資料
| 型號： | LX1744CPW |
| 廠商： | MICROSEMI CORP-ANALOG MIXED SIGNAL GROUP |
| 元件分類： | 顯示驅(qū)動器 |
| 英文描述： | Dual Output Boost ? LED Driver / LCD Bias |
| 中文描述： | LED DISPLAY DRIVER, PDSO14 |
| 封裝： | PLASTIC, TSSOP-14 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 571K |
| 代理商： | LX1744CPW |
LX1744
P
RODUCTION
D
ATASHEET
Microsemi
Integrated Products Division
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 9
W
M
.
C
Dual Output Boost – LED Driver / LCD Bias
I N T E G R A T E D P R O D U C T S
Copyright
2000
Rev. 1.1b, 2005-03-01
A P P L I C A T I O N N O T E
negative voltage transition that is greater than the output
voltage.
P
OWER
M
OSFET
S
ELECTION
The LX1744 can source up to 100mA of gate current.
A logi-level N-channel MOSFET with a low turn on
threshold voltage, low gate charge and low R
DS(ON)
is
required to optimize overall circuit performance.
O
VER
V
OLTAGE
P
ROTECTION
P
ROGRAMMING
Since the output of the LED Driver is a current mode
configuration, it may be desirable to protect the output from
an over-voltage condition in the event the load is removed
or not present.
The LX1744 includes an over voltage monitor that is
easily programmed with two external resistors (Figure 6).
This feature eliminates the need for a Zener Diode clamp on
the output.
Programming is accomplished by first selecting R
OVP_2
and then calculating R
OVP_1
using the following equation.
2
_
OVP
1
_
OVP
R
R
=
REF
REF
OVP
V
V
V
-
eq. 9
where V
OVP
is the desired maximum voltage on the output.
This voltage should be selected to accommodate the
maximum forward voltage of all the LEDs, over
temperature, plus the maximum feedback voltage.
Conversely, it may also be selected according to the
maximum V
DS
voltage of the output MOSFET.
I
NDUCTOR
C
URRENT
L
IMIT
P
ROGRAMMING
Setting of the peak inductor current limit is an important
aspect of the PFM constant off-time architecture; it
determines the maximum output power capability and has a
marked effect on efficiency.
It is recommended that the peak inductor current be set
to approximately two times the expected maximum DC
input current. This setting will minimize the inductor size,
the input ripple current, and the output ripple voltage. Care
should be taken to use inductors that will not saturate at the
peak inductor current level. The desired peak inductor
current can be estimated by the following equation:
PK
2
I
η
where P
OUT
is the total output power,
η
is the expected
conversion efficiency, and V
IN
is the input voltage.
From the calculated desired I
PK
an R
CS
resistance value
IN
OUT
V
P
=
eq. 10
can be chosen from the following equation:
6
PK
30
CS
10
185
.
I
R
eq. 11
which is taken from the following graph (Figure 7).
0
200
400
600
800
1000
0
5
10
15
20
R
CS
(k
)
P
(
Figure 7 –
Peak Current Programming Resistor
This graph characterizes the relationship between peak
inductor current, the inductance value, and the R
CS
programming resistor.
I
NDUCTOR
S
ELECTION
An inductor value of 47
μ
H has been show to yield very
good results. Choosing a lower value emphasizes peak
current overshoot, effectively raises the switching
frequency, and increases the dissipative losses due to
increased currents.
O
UTPUT
C
APACITOR
S
ELECTION
Output voltage ripple is a function of the several
parameters: inductor value, output capacitance value, peak
switch current, load current, input voltage, and the output
voltage. All of these factors can be summarized by the
following equation:
IN
OUT
V
(
V
C
where V
L
is the voltage drop across the inductor, V
F
is the
forward voltage of the output catch diode, and V
SW
is the
voltage drop across the power switch. V
L
+V
SW
can be
approximated at 0.4V and V
F
can be approximated at 0.4V.
+
+
+
IN
F
OUT
V
OUT
V
PK
I
L
SW
OUT
I
PK
I
RIPPLE
V
V
I
)
V
1
L
eq. 12
A
P
P
L
I
C
A
T
I
O
N
S
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| LX1745CPW | 功能描述:IC LED DRVR WT/CLR BCKLT 20TSSOP RoHS:是 類別:集成電路 (IC) >> PMIC - LED 驅(qū)動器 系列:- 標準包裝:1 系列:- 恒定電流:- 恒定電壓:- 拓撲:PWM，切換式電容器（充電泵） 輸出數(shù):1 內(nèi)部驅(qū)動器:是 類型 - 主要:背光 類型 - 次要:白色 LED 頻率:642kHz 電源電壓:2.7 V ~ 5.5 V 輸出電壓:5V 安裝類型:表面貼裝 封裝/外殼:10-VFDFN 裸露焊盤 供應(yīng)商設(shè)備封裝:10-VSON 包裝:剪切帶 (CT) 工作溫度:-30°C ~ 85°C 產(chǎn)品目錄頁面:1371 (CN2011-ZH PDF) 其它名稱:BD1603NUV-E2CT |
| LX1745-CPW | 制造商:MICROSEMI 制造商全稱:Microsemi Corporation 功能描述:Triple Output Boost ? LED Driver / LCD Bias |
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