參數(shù)資料
型號: LM3595LDX
廠商: NATIONAL SEMICONDUCTOR CORP
元件分類: 顯示驅(qū)動器
英文描述: The LM3595 is a parallel white-LED driver that is capable of driving four white LEDs.
中文描述: LED DISPLAY DRIVER, DSO10
封裝: 3 X 3 MM, 0.80 MM HEIGHT, LLP-10
文件頁數(shù): 9/11頁
文件大?。?/td> 233K
代理商: LM3595LDX
Application Information
(Continued)
TABLE 2. LED Current when using the BRGT input with BR-ON = V
IN
4.99k
6.25k
I
LED
(mA)
I
LED
(mA)
0.1
0.1
4.1
3.3
8.1
6.7
12.2
10.0
16.3
13.3
20.4
16.7
24.5
20.0
R
SET
(
)
VBRGT(V)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
8.25k
I
LED
(mA)
0.1
2.5
4.9
7.4
9.9
12.3
14.8
12.4k
I
LED
(mA)
0.1
1.6
3.3
4.9
6.6
8.2
9.8
LED SELECTION
The LM3595 is designed to drive white-LEDs with a typical
forward voltage of 3.0V to 4.0V. The maximum LED forward
voltage that the LM3595 can accommodate is highly depen-
dant upon V
and I
. (See the section on Output Current
Capability for more information on finding maximum V
.)
For applications that demand color and brightness matching,
care must be taken to select LEDs from the same chroma-
ticity group. Forward current matching is assured over the
LED process variations due to the constant current outputs
of the LM3595.
TABLE 3. White LED Selection:
Component Manufacture Contact
Manufacturer
Osram
Nichia
Contact
www.osram-os.com
www.nichia.com
PARALLEL OUTx OUTPUTS FOR INCREASED
CURRENT DRIVE
Outputs OUT1 through OUT4 may be connected together in
any combination to drive higher currents through fewer
LEDs. For example in
Figure 1
, outputs OUT1 and OUT2 are
connected together to drive one LED while OUT3 and OUT4
are connected together to drive a second LED.
With this configuration, two parallel current sources of equal
value provide current to each LED. R
and V
should
therefore be chosen so that the current through each output
is programmed to 50% of the desired current through the
parallel connected LEDs. For example, if 30mA is the de-
sired drive current for 2 parallel connected LEDs, R
and
V
should be selected so that the current through each of
the outputs is 15mA. Other combinations of parallel outputs
may be implemented in similar fashions, such as in
Figure 2
.
Connecting outputs in parallel does not affect internal opera-
tion of the LM3595 and has no impact on the Electrical
Characteristics and limits previously presented. The avail-
able diode output current, maximum diode voltage, and all
other specifications provided in the Electrical Characteristics
table apply to parallel output configurations, just as they do
to the standard 4-LED application circuit.
POWER DISSIPATION
The maximum allowable power dissipation that this package
is capable of handling can be determined as follows:
P
DMax
= (T
JMax
- T
A
) /
θ
JA
Where T
is the maximum junction temperature, T
is the
ambient temperature, and
θ
is the junction-to-ambient
thermal resistance of the specified package. The LM3595
come in the LLP-10 package that has a junction-to-ambient
thermal resistance (
θ
) equal to 55C/W. This value of
θ
is
highly dependant upon the layout of the PC board (See the
PCB Layout Considerations section of this datasheet for
more information). The actual power dissipated by the
LM3595 follows the equation:
P
DISS
=(V
IN
x I
IN
) - N(V
OUTX
x I
OUTX
)
Where N equals the number of active outputs, V
is the
LED forward voltage, and I
OUTX
is the current supplied to the
20072215
FIGURE 1. Two Parallel Connected LEDs
20072216
FIGURE 2. One Parallel Connected LED
L
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9
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