LX1745CPW Microsemi Analog Mixed Signal Group, LX1745CPW Datasheet - Page 10

• Manufacturer Part Number: LX1745CPW
• Description: IC LED DRVR WT/CLR BCKLT 20TSSOP
• Manufacturer: Microsemi Analog Mixed Signal Group
• Type: Backlight, White LED, Color LEDr

Specifications of LX1745CPW

• Constant Current: Yes
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 3
• Internal Driver: Both
• Type - Primary: Backlight
• Type - Secondary: Color, White LED
• Voltage - Supply: 1.6 V ~ 6 V
• Voltage - Output: 25V
• Mounting Type: Surface Mount
• Package / Case: 20-TSSOP
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 100mA
• Internal Switch(s): Yes
• Efficiency: 90%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Frequency: -

Copyright © 2000
Rev. 1.2, 2006-02-27
N
For applications that require it, a negative bias can be
easily generated using an inductorless charge pump
consisting of only four additional discrete components
(Figure 8).
This negative output is a mirror of the positive output
voltage. However, it is unregulated.
possible with some additional components. A low current
shunt regulator (LX6431 or LX432) and a bipolor pass
element can form a simple negative voltage LDO (Figure
9).
R
regulation while R
to be 100kΩ then R
equation:
where V
F
Improved efficiency and ripple performance can be
V
NEG_LCD
3
EED
EGATIVE
If a regulated negative bias is desired then this is also
is sized to meet the minimum shunt current required for
-F
TM
R
R
4
5
ORWARD
REF
- V
V
OUT
OUT
LCD B
is a -2.5V in the case of the LX6431.
Figure 8 – Negative Bias Generation
Figure 9 – Regulated Negative Bias
LX6431,
V
LX432
OUT
V
C
4
IAS
NEG
R
APACITANCE
3
and R
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
_
R
R
4
G
LCD
1
2
ENERATION
is calculated using the following
D
D
3
4
=
5
are calculated. If R
V
R
R
1
2
REF
D
D
3
4
⋅
⎛
⎜ ⎜
⎝
1
+
SWx
R
R
LX1745
V
4
5
BAT
⎞
⎟ ⎟
⎠
FBx
= 1.6V to 6.0V
SWx
V
LX1745
BAT
A P P L I C A T I O N N O T E
FBx
Integrated Products Division
= 1.6V to 6.0V
5
is selected
®
Microsemi
eq. 13
Triple Output Boost – LED Driver / LCD Bias
achieved by placing a feed-forward capacitor across the
feedback resistor connected to the output (Figure 2). A
recommended value of 1nF should be used.
PCB L
diode, input and output capacitors, and feedback
connection (i.e. pin 3) are typical considerations.
Moreover, the designer should maximize the DC input and
output trace widths to accommodate peak current levels
associated with this circuit.
SHDN
Minimizing trace lengths from the IC to the inductor,
0
0
1
1
1
0
1
0
AYOUT
SHDN2
P
0
1
0
1
1
1
0
0
RODUCTION
Table 1
SHDN1
1
1
1
1
0
0
0
0
–
D
Enable Logic
ATASHEET
LCD1
1
1
1
1
0
0
0
0
LCD2
0
1
0
1
0
0
0
0
LX1745
LED
0
0
1
1
0
0
0
0
Page 10